This document is obsolete. Please
refer to RFC 2622.
Network Working Group C. Alaettinoglu Request for Comments: 2280 USC/Information Sciences Institute Category: Standards Track T. Bates Cisco Systems E. Gerich At Home Network D. Karrenberg RIPE D. Meyer University of Oregon M. Terpstra Bay Networks C. Villamizar ANS January 1998
Routing Policy Specification Language (RPSL)
Status of this Memo
This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (1998). All Rights Reserved.
This memo is the reference document for the Routing Policy Specification Language (RPSL). RPSL allows a network operator to be able to specify routing policies at various levels in the Internet hierarchy; for example at the Autonomous System (AS) level. At the same time, policies can be specified with sufficient detail in RPSL so that low level router configurations can be generated from them. RPSL is extensible; new routing protocols and new protocol features can be introduced at any time.
RPSL is a replacement for the current Internet policy specification language known as RIPE-181 [4] or RFC-1786 [5]. RIPE-81 [6] was the first language deployed in the Internet for specifying routing policies. It was later replaced by RIPE-181 [4]. Through operational use of RIPE-181 it has become apparent that certain policies cannot be specified and a need for an enhanced and more generalized language is needed. RPSL addresses RIPE-181's limitations.
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RPSL was designed so that a view of the global routing policy can be contained in a single cooperatively maintained distributed database to improve the integrity of Internet's routing. RPSL is not designed to be a router configuration language. RPSL is designed so that router configurations can be generated from the description of the policy for one autonomous system (aut-num class) combined with the description of a router (inet-rtr class), mainly providing router ID, autonomous system number of the router, interfaces and peers of the router, and combined with a global database mappings from AS sets to ASes (as-set class), and from origin ASes and route sets to route prefixes (route and route-set classes). The accurate population of the RPSL database can help contribute toward such goals as router configurations that protect against accidental (or malicious) distribution of inaccurate routing information, verification of Internet's routing, and aggregation boundaries beyond a single AS.
RPSL is object oriented; that is, objects contain pieces of policy and administrative information. These objects are registered in the Internet Routing Registry (IRR) by the authorized organizations. The registration process is beyond the scope of this document. Please refer to [1, 15, 2] for more details on the IRR.
In the following sections, we present the classes that are used to define various policy and administrative objects. The "mntner" class defines entities authorized to add, delete and modify a set of objects. The "person" and "role" classes describes technical and administrative contact personnel. Autonomous systems (ASes) are specified using the "aut-num" class. Routes are specified using the "route" class. Sets of ASes and routes can be defined using the "as-set" and "route-set" classes. The "dictionary" class provides the extensibility to the language. The "inet-rtr" class is used to specify routers. Many of these classes were originally defined in earlier documents [4, 11, 14, 10, 3] and have all been enhanced.
This document is self-contained. However, the reader is encouraged to read RIPE-181 [5] and the associated documents [11, 14, 10, 3] as they provide significant background as to the motivation and underlying principles behind RIPE-181 and consequently, RPSL. For a tutorial on RPSL, the reader should read the RPSL applications document [2].
Each class has a set of attributes which store a piece of information about the objects of the class. Attributes can be mandatory or optional: A mandatory attribute has to be defined for all objects of
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the class; optional attributes can be skipped. Attributes can also be single or multiple valued. Each object is uniquely identified by a set of attributes, referred to as the class "key".
The value of an attribute has a type. The following types are most widely used. Note that RPSL is case insensitive and only the characters from the ASCII character set can be used.
<object-name>Many objects in RPSL have a name. An <object-name> is made up of letters, digits, the character underscore "_", and the character hyphen "-"; the first character of a name must be a letter, and the last character of a name must be a letter or a digit. The following words are reserved by RPSL, and they can not be used as names:
any as-any rs-any peeras and or not atomic from to at action accept announce except refine networks into inbound outbound
Names starting with certain prefixes are reserved for certain object types. Names starting with "as-" are reserved for as set names. Names starting with "rs-" are reserved for route set names.
<as-number>An AS number x is represented as the string "ASx". That is, the AS 226 is represented as AS226.
<ipv4-address>An IPv4 address is represented as a sequence of four integers in the range from 0 to 255 separated by the character dot ".". For example, 128.9.128.5 represents a valid IPv4 address. In the rest of this document, we may refer to IPv4 addresses as IP addresses.
<address-prefix>An address prefix is represented as an IPv4 address followed by the character slash "/" followed by an integer in the range from 0 to 32. The following are valid address prefixes: 128.9.128.5/32, 128.9.0.0/16, 0.0.0.0/0; and the following address prefixes are invalid: 0/0, 128.9/16 since 0 or 128.9 are not strings containing four integers.
<address-prefix-range>An address prefix range is an address prefix followed by one of the following range operators:
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^- is the exclusive more specifics operator; it stands for the more specifics of the address prefix excluding the address prefix itself. For example, 128.9.0.0/16^- contains all the more specifics of 128.9.0.0/16 excluding 128.9.0.0/16.
^+ is the inclusive more specifics operator; it stands for the more specifics of the address prefix including the address prefix itself. For example, 5.0.0.0/8^+ contains all the more specifics of 5.0.0.0/8 including 5.0.0.0/8.
^n where n is an integer, stands for all the length n specifics of the address prefix. For example, 30.0.0.0/8^16 contains all the more specifics of 30.0.0.0/8 which are of length 16 such as 30.9.0.0/16.
^n-m where n and m are integers, stands for all the length n to length m specifics of the address prefix. For example, 30.0.0.0/8^24-32 contains all the more specifics of 30.0.0.0/8 which are of length 24 to 32 such as 30.9.9.96/28.
Range operators can also be applied to address prefix sets. In this case, they distribute over the members of the set. For example, for a route-set (defined later) rs-foo, rs-foo^+ contains all the inclusive more specifics of all the prefixes in rs-foo.
<date>A date is represented as an eight digit integer of the form YYYYMMDD where YYYY represents the year, MM represents the month of the year (01 through 12), and DD represents the day of the month (01 through 31). For example, June 24, 1996 is represented as 19960624.
<nic-handle>is a uniquely assigned identifier[13] used by routing, address allocation, and other registries to unambiguously refer to contact information. person and role classes map NIC handles to actual person names, and contact information.
<free-form>is a sequence of ASCII characters.
<X-name>is a name of an object of type X. That is <mntner-name> is a name of a mntner object.
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<registry-name>is a name of an IRR registry. The routing registries are listed in Appendix A.
A value of an attribute may also be a list of one of these types. A list is represented by separating the list members by commas ",". For example, "AS1, AS2, AS3, AS4" is a list of AS numbers. Note that being list valued and being multiple valued are orthogonal. A multiple valued attribute has more than one value, each of which may or may not be a list. On the other hand a single valued attribute may have a list value.
An RPSL object is textually represented as a list of attribute-value pairs. Each attribute-value pair is written on a separate line. The attribute name starts at column 0, followed by character ":" and followed by the value of the attribute. The object's representation ends when a blank line is encountered. An attribute's value can be split over multiple lines, by starting the continuation lines with a white-space (" " or tab) character. The order of attribute-value pairs is significant.
An object's description may contain comments. A comment can be anywhere in an object's definition, it starts at the first "#" character on a line and ends at the first end-of-line character. White space characters can be used to improve readability.
The mntner, person and role classes, admin-c, tech-c, mnt-by, changed, and source attributes of all classes describe contact information. The mntner class also specifies what entities can create, delete and update other objects. These classes do not specify routing policies and each registry may have different or additional requirements on them. Here we present the common denominator for completeness which is the RIPE database implementation[15]. Please consult your routing registry for the latest specification of these classes and attributes.
The mntner class defines entities that can create, delete and update RPSL objects. A provider, before he/she can create RPSL objects, first needs to create a mntner object. The attributes of the mntner class are shown in Figure 1. The mntner class was first described in [11].
The mntner attribute is mandatory and is the class key attribute. Its value is an RPSL name. The auth attribute specifies the scheme that will be used
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Attribute Value Type mntner <object-name> mandatory, single-valued, class key descr <free-form> mandatory, single-valued auth see description in text mandatory, multi-valued upd-to <email-address> mandatory, multi-valued mnt-nfy <email-address> optional, multi-valued tech-c <nic-handle> mandatory, multi-valued admin-c <nic-handle> mandatory, multi-valued remarks <free-form> optional, multi-valued notify <email-address> optional, multi-valued mnt-by list of <mntner-name> mandatory, multi-valued changed <email-address> <date> mandatory, multi-valued source <registry-name> mandatory, single-valued
to identify and authenticate update requests from this maintainer. It has the following syntax:
auth: <scheme-id> <auth-info>
E.g. auth: NONE auth: CRYPT-PW dhjsdfhruewf auth: MAIL-FROM .*@ripe\.net
The <scheme-id>'s currently defined are: NONE, MAIL-FROM, PGP and CRYPT-PW. The <auth-info> is additional information required by a particular scheme: in the case of MAIL-FROM, it is a regular expression matching valid email addresses; in the case of CRYPT-PW, it is a password in UNIX crypt format; and in the case of PGP, it is a PGP public key. If multiple auth attributes are specified, an update request satisfying any one of them is authenticated to be from the maintainer.
The upd-to attribute is an email address. On an unauthorized update attempt of an object maintained by this maintainer, an email message will be sent to this address. The mnt-nfy attribute is an email address. A notification message will be forwarded to this email address whenever an object maintained by this maintainer is added, changed or deleted.
The descr attribute is a short, free-form textual description of the object. The tech-c attribute is a technical contact NIC handle. This is someone to be contacted for technical problems such as misconfiguration. The admin-c attribute is an administrative contact NIC handle. The remarks attribute is a free text explanation or clarification. The notify attribute is an email address to which notifications of changes to this object should be sent. The mnt-by attribute is a list of mntner object names. The authorization for
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changes to this object is governed by any of the maintainer objects referenced. The changed attribute documents who last changed this object, and when this change was made. Its syntax has the following form:
changed: <email-address> <YYYYMMDD>
E.g. changed: johndoe@terabit-labs.nn 19900401
The <email-address> identifies the person who made the last change. <YYYYMMDD> is the date of the change. The source attribute specifies the registry where the object is registered. Figure 2 shows an example mntner object. In the example, UNIX crypt format password authentication is used.
The descr, tech-c, admin-c, remarks, notify, mnt-by, changed and source attributes are attributes of all RPSL classes. Their syntax, semantics, and mandatory, optional, multi-valued, or single-valued status are the same for for all RPSL classes. We do not further discuss them in other sections.
A person class is used to describe information about people. Even though it does not describe routing policy, we still describe it here briefly since many policy objects make reference to person objects. The person class was first described in [14].
The attributes of the person class are shown in Figure 3. The person attribute is the full name of the person. The phone and the fax-no attributes have the following syntax:
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Attribute Value Type person <free-form> mandatory, single-valued nic-hdl <nic-handle> mandatory, single-valued, class key address <free-form> mandatory, multi-valued phone see description in text mandatory, multi-valued fax-no same as phone optional, multi-valued e-mail <email-address> mandatory, multi-valued
The role class is similar to the person object. However, instead of describing a human being, it describes a role performed by one or more human beings. Examples include help desks, network monitoring centers, system administrators, etc. Role object is particularly useful since often a person performing a role may change, however the role itself remains.
The attributes of the role class are shown in Figure 5. The nic-hdl attributes of the person and role classes share the same name space. The
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Attribute Value Type role <free-form> mandatory, single-valued nic-hdl <nic-handle> mandatory, single-valued, class key trouble <free-form> optional, multi-valued address <free-form> mandatory, multi-valued phone see description in text mandatory, multi-valued fax-no same as phone optional, multi-valued e-mail <email-address> mandatory, multi-valued
Figure 5: role Class Attributes
NIC handle of a role object cannot be used in an admin-c field. The trouble attribute of role object may contain additional contact information to be used when a problem arises in any object that references this role object. Figure 6 shows an example role object.
Each interAS route (also referred to as an interdomain route) originated by an AS is specified using a route object. The attributes of the route class are shown in Figure 7. The route attribute is the address prefix of the route and the origin attribute is the AS number of the AS that originates the route into the interAS routing system. The route and origin attribute pair is the class key.
Figure 8 shows examples of four route objects (we do not include contact.
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Attribute Value Type route <address-prefix> mandatory, single-valued, class key origin <as-number> mandatory, single-valued, class key withdrawn <date> optional, single-valued member-of list of <route-set-names> optional, single-valued see Section 5 inject see Section 8 optional, multi-valued components see Section 8 optional, single-valued aggr-bndry see Section 8 optional, single-valued aggr-mtd see Section 8 optional, single-valued export-comps see Section 8 optional, single-valued holes see Section 8 optional, single-valued
Figure 7: route Class Attributes
attributes such as admin-c, tech-c for brevity). Note that the last two route objects have the same address prefix, namely 128.8.0.0/16. However, they are different route objects since they are originated by different ASes (i.e. they have different keys).
The withdrawn attribute, if present, signifies that the originator AS no longer originates this address prefix in the Internet. Its value is a date indicating the date of withdrawal. In Figure 8, the last route object is withdrawn (i.e. no longer originated by AS2) on June 24, 1996.
To specify policies, it is often useful to define sets of objects. For this purpose we define two classes: route-set and as-set. These classes define a named set. The members of these sets can be specified by either explicitly listing them in the set object's definition, or implicitly by having route and aut-num objects refer to the set names, or a combination of both methods.
The attributes of the route-set class are shown in Figure 9. The route-set attribute defines the name of the set. It is an RPSL name that starts with "rs-". The members attribute lists the members of the set. The members attribute is a list of address prefixes or other route-set names. Note that, the route-set class is a set of route prefixes, not of RPSL route objects.
Attribute Value Type route-set <object-name> mandatory, single-valued, class key members list of <address-prefixes> or optional, single-valued <route-set-names> mbrs-by-ref list of <mntner-names> optional, single-valued
Figure 9: route-set Class Attributes
Figure 10 presents some example route-set objects. The set rs-foo contains two address prefixes, namely 128.9.0.0/16 and 128.9.0.0/16. The set rs-bar contains the members of the set rs-foo and the address prefix 128.7.0.0/16. The set rs-empty contains no members.
contains all the more specifics of 5.0.0.0/8 including 5.0.0.0/8, all the more specifics of 30.0.0.0/8 which are of length 24 to 32 such as 30.9.9.96/28, and all the more specifics of address prefixes in route set rs-foo.
The mbrs-by-ref attribute is a list of maintainer names or the keyword ANY. If this attribute is used, the route set also includes address prefixes whose route objects are registered by one of these maintainers and whose member-of attribute refers to the name of this route set. If the value of a mbrs-by-ref attribute is ANY, any route object referring to the route set name is a member. If the mbrs-by- ref attribute is missing, only the address prefixes listed in the members attribute are members of the set.
Figure 11 presents example route-set objects that use the mbrs-by-ref attribute. The set rs-foo contains two address prefixes, namely 128.8.0.0/16 and 128.9.0.0/16 since the route objects for 128.8.0.0/16 and 128.9.0.0/16 refer to the set name rs-foo in their member-of attribute. The set rs-bar contains the address prefixes 128.7.0.0/16 and 128.8.0.0/16. The route 128.7.0.0/16 is explicitly listed in the members attribute of rs-bar, and the route object for 128.8.0.0/16 refer to the set name rs-bar in its member-of attribute.
Note that, if an address prefix is listed in a members attribute of a route set, it is a member of that route set. The route object
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corresponding to this address prefix does not need to contain a member-of attribute referring to this set name. The member-of attribute of the route class is an additional mechanism for specifying the members indirectly.
The attributes of the as-set class are shown in Figure 12. The as- set attribute defines the name of the set. It is an RPSL name that starts with "as-". The members attribute lists the members of the set. The members attribute is a list of AS numbers, or other as-set names.
Attribute Value Type as-set <object-name> mandatory, single-valued, class key members list of <as-numbers> or optional, single-valued <as-set-names> mbrs-by-ref list of <mntner-names> optional, single-valued
Figure 12: as-set Class Attributes
Figure 13 presents two as-set objects. The set as-foo contains two ASes, namely AS1 and AS2. The set as-bar contains the members of the set as-foo and AS3, that is it contains AS1, AS2, AS3.
The mbrs-by-ref attribute is a list of maintainer names or the keyword ANY. If this attribute is used, the AS set also includes ASes whose aut-num objects are registered by one of these maintainers and whose member-of attribute refers to the name of this AS set. If the value of a mbrs-by-ref attribute is ANY, any AS object referring to the AS set is a member of the set. If the mbrs-by-ref attribute is missing, only the ASes listed in the members attribute are members of the set.
Figure 14 presents an example as-set object that uses the mbrs-by-ref attribute. The set as-foo contains AS1, AS2 and AS3. AS4 is not a member of the set as-foo even though the aut-num object references as-foo. This is because MNTR-OTHER is not listed in the as-foo's mbrs-by-ref attribute.
In a context that expects a route set (e.g. members attribute of the route-set class), an AS number ASx defines the set of routes that are originated by ASx; and an as-set AS-X defines the set of routes that are originated by the ASes in AS-X. A route p is said to be originated by ASx if there is a route object for p with ASx as the value of the origin attribute. For example, in Figure 15, the route set rs-special contains 128.9.0.0/16, routes of AS1 and AS2, and routes of the ASes in AS set AS-FOO.
Set names can be hierarchical. A hierarchical set name is a sequence of set names and AS numbers separated by colons ":". For example, the following names are valid: AS1:AS-CUSTOMERS, AS1:RS-EXCEPTIONS, AS1:RS-EXPORT:AS2, RS-EXCEPTIONS:RS-BOGUS. All components of an hierarchical set name which are not AS numbers should start with "as-" or "rs-" for as sets and route sets respectively.
A set object with name X1:...:Xn-1:Xn can only be created by the maintainer of the object with name X1:...:Xn-1. That is, only the maintainer of AS1 can create a set with name AS1:AS-FOO; and only the maintainer of AS1:AS-FOO can create a set with name AS1:AS-FOO:AS- BAR.
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The purpose of an hierarchical set name is to partition the set name space so that the controllers of the set name X1 controls the whole set name space under X1, i.e. X1:...:Xn-1. This is important since anyone can create a set named AS-MCI-CUSTOMERS but only the people created AS3561 can create AS3561:AS-CUSTOMERS. In the former, it is not clear if the set AS-MCI-CUSTOMERS has any relationship with MCI. In the latter, we can guarantee that AS3561:AS-CUSTOMERS and AS3561 are created by the same entity.
ASes are specified using the aut-num class. The attributes of the aut-num class are shown in Figure 16. The value of the aut-num attribute is the AS number of the AS described by this object. The as-name attribute is a symbolic name (in RPSL name syntax) of the AS. The import, export and default routing policies of the AS are specified using import, export and default attributes respectively.
Attribute Value Type aut-num <as-number> mandatory, single-valued, class key as-name <object-name> mandatory, single-valued member-of list of <as-set-names> optional, single-valued import see Section 6.1 optional, multi valued export see Section 6.2 optional, multi valued default see Section 6.5 optional, multi valued
Figure 17 shows a typical interconnection of ASes that we will be using in our examples throughout this section. In this example topology, there are three ASes, AS1, AS2, and AS3; two exchange points, EX1 and EX2; and six routers. Routers connected to the same exchange point peer with each other, i.e. open a connection for exchanging routing information. Each router would export a subset of the routes it has to its peer routers. Peer routers would import a subset of these routes. A router while importing routes would set some route attributes. For example, AS1 can assign higher preference values to the routes it imports from AS2 so that it prefers AS2 over AS3. While exporting routes, a router may also set some route attributes in order to affect route selection by its peers. For example, AS2 may set the MULTI-EXIT-DISCRIMINATOR BGP attribute so that AS1 prefers to use the router 9.9.9.2. Most interAS policies are specified by specifying what route subsets can be imported or exported, and how the various BGP route attributes are set and used.
Figure 17: Example topology consisting of three ASes, AS1, AS2, and AS3; two exchange points, EX1 and EX2; and six routers.
In RPSL, an import policy is divided into import policy expressions. Each import policy expression is specified using an import attribute. The import attribute has the following syntax (we will extend this syntax later in Sections 6.3 and 6.6):
import: from <peering-1> [action <action-1>] . . . from <peering-N> [action <action-N>] accept <filter>
The action specification is optional. The semantics of an import attribute is as follows: the set of routes that are matched by <filter> are imported from all the peers in <peerings>; while importing routes at <peering-M>, <action-M> is executed.
E.g. aut-num: AS1 import: from AS2 action pref = 1; accept { 128.9.0.0/16 }
This example states that the route 128.9.0.0/16 is accepted from AS2 with preference 1. In the next few subsections, we will describe how peerings, actions and filters are specified.
Our example above used an AS number to specify peerings. The peerings can be specified at different granularities. The syntax of a peering specification has two forms. The first one is as follows:
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<peer-as> [<peer-router>] [at <local-router>]
where <local-router> and <peer-router> are IP addresses of routers, <peer-as> is an AS number. <peer-as> must be the AS number of <peer-router>. Both <local-router> and <peer-router> are optional. If both <local-router> and <peer-router> are specified, this peering specification identifies only the peering between these two routers. If only <local-router> is specified, this peering specification identifies all the peerings between <local-router> and any of its peer routers in <peer-as>. If only <peer-router> is specified, this peering specification identifies all the peerings between any router in the local AS and <peer-router>. If neither <local-router> nor <peer-router> is specified, this peering specification identifies all the peerings between any router in the local AS and any router in <peer-as>.
We next give examples. Consider the topology of Figure 17 where 7.7.7.1, 7.7.7.2 and 7.7.7.3 peer with each other; 9.9.9.1, 9.9.9.2 and 9.9.9.3 peer with each other. In the following example 7.7.7.1 imports 128.9.0.0/16 from 7.7.7.2.
(1) aut-num: AS1 import: from AS2 7.7.7.2 at 7.7.7.1 accept { 128.9.0.0/16 }
In the following example 7.7.7.1 imports 128.9.0.0/16 from 7.7.7.2 and 7.7.7.3.
(2) aut-num: AS1 import: from AS2 at 7.7.7.1 accept { 128.9.0.0/16 }
In the following example 7.7.7.1 imports 128.9.0.0/16 from 7.7.7.2 and 7.7.7.3, and 9.9.9.1 imports 128.9.0.0/16 from 9.9.9.2.
(3) aut-num: AS1 import: from AS2 accept { 128.9.0.0/16 }
The second form of <peering> specification has the following syntax:
<as-expression> [at <router-expression>]
where <as-expression> is an expression over AS numbers and sets using operators AND, OR, and NOT, and <router-expression> is an expression over router IP addresses and DNS names using operators AND, OR, and NOT. The DNS name can only be used if there is an inet-rtr object for that name that binds the name to IP addresses. This form identifies all the peerings between any local router in <router-expression> to
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any of their peer routers in the ASes in <as-expression>. If <router-expression> is not specified, it defaults to all routers of the local AS.
In the following example 9.9.9.1 imports 128.9.0.0/16 from 9.9.9.2 and 9.9.9.3.
(4) as-set: AS-FOO members: AS2, AS3 aut-num: AS1 import: from AS-FOO at 9.9.9.1 accept { 128.9.0.0/16 }
In the following example 9.9.9.1 imports 128.9.0.0/16 from 9.9.9.2 and 9.9.9.3, and 7.7.7.1 imports 128.9.0.0/16 from 7.7.7.2 and 7.7.7.3.
(5) aut-num: AS1 import: from AS-FOO accept { 128.9.0.0/16 }
In the following example AS1 imports 128.9.0.0/16 from AS3 at router 9.9.9.1
(6) aut-num: AS1 import: from AS-FOO and not AS2 at not 7.7.7.1 accept { 128.9.0.0/16 }
This is because "AS-FOO and not AS2" equals AS3 and "not 7.7.7.1" equals 9.9.9.1.
Policy actions in RPSL either set or modify route attributes, such as assigning a preference to a route, adding a BGP community to the BGP community path attribute, or setting the MULTI-EXIT-DISCRIMINATOR attribute. Policy actions can also instruct routers to perform special operations, such as route flap damping.
The routing policy attributes whose values can be modified in policy actions are specified in the RPSL dictionary. Please refer to Section 7 for a list of these attributes. Each action in RPSL is terminated by the character ';'. It is possible to form composite policy actions by listing them one after the other. In a composite policy action, the actions are executed left to right. For example,
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aut-num: AS1 import: from AS2 action pref = 10; med = 0; community.append(10250, {3561,10}); accept { 128.9.0.0/16 }
sets pref to 10, med to 0, and then appends 10250 and {3561,10} to the community path attribute.
A policy filter is a logical expression which when applied to a set of routes returns a subset of these routes. We say that the policy filter matches the subset returned. The policy filter can match routes using any path attribute, such as the destination address prefix (or NLRI), AS-path, or community attributes.
The policy filters can be composite by using the operators AND, OR, and NOT. The following policy filters can be used to select a subset of routes:
ANY The filter-keyword ANY matches all routes.
Address-Prefix Set This is an explicit list of address prefixes enclosed in braces '{' and '}'. The policy filter matches the set of routes whose destination address-prefix is in the set. For example:
contains all the more specifics of 5.0.0.0/8 including 5.0.0.0/8, all the more specifics of 128.9.0.0/16 excluding 128.9.0.0/16, all the more specifics of 30.0.0.0/8 which are of length 16 such as 30.9.0.0/16, and all the more specifics of 30.0.0.0/8 which are of length 24 to 32 such as 30.9.9.96/28.
Route Set Name A route set name matches the set of routes that are members of the set. A route set name may be a name of a route-set object, an AS number, or a name of an as-set object (AS numbers and as-set names implicitly define route sets; please see Section 5.3). For example:
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aut-num: AS1 import: from AS2 action pref = 1; accept AS2 import: from AS2 action pref = 1; accept AS-FOO import: from AS2 action pref = 1; accept RS-FOO
The keyword PeerAS can be used instead of the AS number of the peer AS. PeerAS is particularly useful when the peering is specified using an AS expression. For example:
aut-num: AS1 import: from AS2 action pref = 1; accept AS2 import: from AS3 action pref = 1; accept AS3
A route set name can also be followed by one of the operators '^-', '^+', '^n' or '^n-m'. These operators are distributive over the route sets. For example, { 5.0.0.0/8, 6.0.0.0/8 }^+ equals { 5.0.0.0/8^+, 6.0.0.0/8^+ }, and AS1^- equals all the exclusive more specifics of routes originated by AS1.
AS Path Regular Expressions An AS-path regular expression can be used as a policy filter by enclosing the expression in `<' and `>'. An AS-path policy filter matches the set of routes which traverses a sequence of ASes matched by the AS-path regular expression. A router can check this using the AS_PATH attribute in the Border Gateway Protocol [18], or the RD_PATH attribute in the Inter-Domain Routing Protocol[17].
AS-path Regular Expressions are POSIX compliant regular expressions over the alphabet of AS numbers. The regular expression constructs are as follows:
ASN where ASN is an AS number. ASN matches the AS-path that is of length 1 and contains the corresponding AS number (e.g. AS-path regular expression AS1 matches the AS-path "1").
The keyword PeerAS can be used instead of the AS number of the peer AS.
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AS-set where AS-set is an AS set name. AS-set matches the AS-paths that is matched by one of the ASes in the AS-set.
. matches the AS-paths matched by any AS number.
[...] is an AS number set. It matches the AS-paths matched by the AS numbers listed between the brackets. The AS numbers in the set are separated by white space characters. If a `-' is used between two AS numbers in this set, all AS numbers between the two AS numbers are included in the set. If an as-set name is listed, all AS numbers in the as-set are included.
[^...] is a complemented AS number set. It matches any AS-path which is not matched by the AS numbers in the set.
^ Matches the empty string at the beginning of an AS-path.
$ Matches the empty string at the end of an AS-path.
We next list the regular expression operators in the decreasing order of evaluation. These operators are left associative, i.e. performed left to right.
Unary postfix operators * + ? {m} {m,n} {m,} For a regular expression A, A* matches zero or more occurrences of A; A+ matches one or more occurrences of A; A? matches zero or one occurrence of A; A{m} matches m occurrence of A; A{m,n} matches m to n occurrence of A; A{m,} matches m or more occurrence of A. For example, [AS1 AS2]{2} matches AS1 AS1, AS1 AS2, AS2 AS1, and AS2 AS2.
Unary postfix operators ~* ~+ ~{m} ~{m,n} ~{m,} These operators have similar functionality as the corresponding operators listed above, but all occurrences of the regular expression has to match the same pattern. For example, [AS1 AS2]~{2} matches AS1 AS1 and AS2 AS2, but it does not match AS1 AS2 and AS2 AS1.
Binary catenation operator This is an implicit operator and exists between two regular expressions A and B when no other explicit operator is specified. The resulting expression A B matches an AS-path if A matches some prefix of the AS- path and B matches the rest of the AS-path.
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Binary alternative (or) operator | For a regular expressions A and B, A | B matches any AS-path that is matched by A or B.
Parenthesis can be used to override the default order of evaluation. White spaces can be used to increase readability.
The first example matches any route whose AS-path contains AS3, the second matches routes whose AS-path starts with AS1, the third matches routes whose AS-path ends with AS2, the fourth matches routes whose AS-path is exactly "1 2 3", and the fifth matches routes whose AS-path starts with AS1 and ends in AS2 with any number of AS numbers in between.
Composite Policy Filters The following operators (in decreasing order of evaluation) can be used to form composite policy filters:
NOT Given a policy filter x, NOT x matches the set of routes that are not matched by x. That is it is the negation of policy filter x.
AND Given two policy filters x and y, x AND y matches the intersection of the routes that are matched by x and that are matched by y.
OR Given two policy filters x and y, x OR y matches the union of the routes that are matched by x and that are matched by y.
Note that an OR operator can be implicit, that is `x y' is equivalent to `x OR y'.
E.g.
NOT {128.9.0.0/16, 128.8.0.0/16} AS226 AS227 OR AS228 AS226 AND NOT {128.9.0.0/16} AS226 AND {0.0.0.0/0^0-18}
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The first example matches any route except 128.9.0.0/16 and 128.8.0.0/16. The second example matches the routes of AS226, AS227 and AS228. The third example matches the routes of AS226 except 128.9.0.0/16. The fourth example matches the routes of AS226 whose length are not longer than 18.
Routing Policy Attributes Policy filters can also use the values of other attributes for comparison. The attributes whose values can be used in policy filters are specified in the RPSL dictionary. Please refer to Section 7 for details. An example using the the BGP community attribute is shown below:
aut-num: AS1 export: to AS2 announce AS1 AND NOT community.contains(NO_EXPORT)
Filters using the routing policy attributes defined in the dictionary are evaluated before evaluating the operators AND, OR and NOT.
aut-num: AS1 import: from AS2 action pref = 1; from AS3 action pref = 2; accept AS4
The above example states that AS4's routes are accepted from AS2 with preference 1, and from AS3 with preference 2 (routes with lower integer preference values are preferred over routes with higher integer preference values).
aut-num: AS1 import: from AS2 7.7.7.2 at 7.7.7.1 action pref = 1; from AS2 action pref = 2; accept AS4
The above example states that AS4's routes are accepted from AS2 on peering 7.7.7.1-7.7.7.2 with preference 1, and on any other peering with AS2 with preference 2.
Similarly, an export policy expression is specified using an export attribute. The export attribute has the following syntax:
export: to <peering-1> [action <action-1>] . . . to <peering-N> [action <action-N>] announce <filter>
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The action specification is optional. The semantics of an export attribute is as follows: the set of routes that are matched by <filter> are exported to all the peers specified in <peerings>; while exporting routes at <peering-M>, <action-M> is executed.
E.g. aut-num: AS1 export: to AS2 action med = 5; community .= 70; announce AS4
In this example, AS4's routes are announced to AS2 with the med attribute's value set to 5 and community 70 added to the community list.
Example:
aut-num: AS1 export: to AS-FOO announce ANY
In this example, AS1 announces all of its routes to the ASes in the set AS-FOO.
6.3 Other Routing Protocols, Multi-Protocol Routing Protocols, and Injecting Routes Between Protocols
The more complete syntax of the import and export attributes are as follows:
import: [protocol <protocol-1>] [into <protocol-2>] from <peering-1> [action <action-1>] . . . from <peering-N> [action <action-N>] accept <filter> export: [protocol <protocol-1>] [into <protocol-2>] to <peering-1> [action <action-1>] . . . to <peering-N> [action <action-N>] announce <filter>
Where the optional protocol specifications can be used for specifying policies for other routing protocols, or for injecting routes of one protocol into another protocol, or for multi-protocol routing policies. The valid protocol names are defined in the dictionary. The <protocol-1> is the name of the protocol whose routes are being exchanged. The <protocol-2> is the name of the protocol which is receiving these routes. Both <protocol-1> and <protocol-2> default to the Internet Exterior Gateway Protocol, currently BGP.
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In the following example, all interAS routes are injected into RIP.
aut-num: AS1 import: from AS2 accept AS2 export: protocol BGP4 into RIP to AS1 announce ANY
In the following example, AS1 accepts AS2's routes including any more specifics of AS2's routes, but does not inject these extra more specific routes into OSPF.
aut-num: AS1 import: from AS2 accept AS2^+ export: protocol BGP4 into OSPF to AS1 announce AS2
In the following example, AS1 injects its static routes (routes which are members of the set AS1:RS-STATIC-ROUTES) to the interAS routing protocol and appends AS1 twice to their AS paths.
aut-num: AS1 import: protocol STATIC into BGP4 from AS1 action aspath.prepend(AS1, AS1); accept AS1:RS-STATIC-ROUTES
In the following example, AS1 imports different set of unicast routes for multicast reverse path forwarding from AS2:
aut-num: AS1 import: from AS2 accept AS2 import: protocol IDMR from AS2 accept AS2:RS-RPF-ROUTES
It is possible that the same peering can be covered by more that one peering specification in a policy expression. For example:
aut-num: AS1 import: from AS2 7.7.7.2 at 7.7.7.1 action pref = 2; from AS2 7.7.7.2 at 7.7.7.1 action pref = 1; accept AS4
This is not an error, though definitely not desirable. To break the ambiguity, the action corresponding to the first peering specification is used. That is the routes are accepted with preference 2. We call this rule as the specification-order rule.
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Consider the example:
aut-num: AS1 import: from AS2 action pref = 2; from AS2 7.7.7.2 at 7.7.7.1 action pref = 1; dpa = 5; accept AS4
where both peering specifications cover the peering 7.7.7.1-7.7.7.2, though the second one covers it more specifically. The specification order rule still applies, and only the action "pref = 2" is executed. In fact, the second peering-action pair has no use since the first peering-action pair always covers it. If the intended policy was to accept these routes with preference 1 on this particular peering and with preference 2 in all other peerings, the user should have specified:
aut-num: AS1 import: from AS2 7.7.7.2 at 7.7.7.1 action pref = 1; dpa = 5; from AS2 action pref = 2; accept AS4
It is also possible that more than one policy expression can cover the same set of routes for the same peering. For example:
aut-num: AS1 import: from AS2 action pref = 2; accept AS4 import: from AS2 action pref = 1; accept AS4
In this case, the specification-order rule is still used. That is, AS4's routes are accepted from AS2 with preference 2. If the filters were overlapping but not exactly the same:
aut-num: AS1 import: from AS2 action pref = 2; accept AS4 import: from AS2 action pref = 1; accept AS4 OR AS5
the AS4's routes are accepted from AS2 with preference 2 and however AS5's routes are also accepted, but with preference 1.
We next give the general specification order rule for the benefit of the RPSL implementors. Consider two policy expressions:
aut-num: AS1 import: from peerings-1 action action-1 accept filter-1 import: from peerings-2 action action-2 accept filter-2
The above policy expressions are equivalent to the following three expressions where there is no ambiguity:
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aut-num: AS1 import: from peerings-1 action action-1 accept filter-1 import: from peerings-3 action action-2 accept filter-2 AND NOT filter-1 import: from peerings-4 action action-2 accept filter-2
where peerings-3 are those that are covered by both peerings-1 and peerings-2, and peerings-4 are those that are covered by peerings-2 but not by peerings-1 ("filter-2 AND NOT filter-1" matches the routes that are matched by filter-2 but not by filter-1).
Example:
aut-num: AS1 import: from AS2 7.7.7.2 at 7.7.7.1 action pref = 2; accept {128.9.0.0/16} import: from AS2 action pref = 1; accept {128.9.0.0/16, 75.0.0.0/8}
Lets consider two peerings with AS2, 7.7.7.1-7.7.7.2 and 9.9.9.1- 9.9.9.2. Both policy expressions cover 7.7.7.1-7.7.7.2. On this peering, the route 128.9.0.0/16 is accepted with preference 2, and the route 75.0.0.0/8 is accepted with preference 1. The peering 9.9.9.1-9.9.9.2 is only covered by the second policy expressions. Hence, both the route 128.9.0.0/16 and the route 75.0.0.0/8 are accepted with preference 1 on peering 9.9.9.1-9.9.9.2.
Note that the same ambiguity resolution rules also apply to export and default policy expressions.
Default routing policies are specified using the default attribute. The default attribute has the following syntax:
default: to <peering> [action <action>] [networks <filter>]
The <action> and <filter> specifications are optional. The semantics are as follows: The <peering> specification indicates the AS (and the router if present) is being defaulted to; the <action> specification, if present, indicates various attributes of defaulting, for example a relative preference if multiple defaults are specified; and the <filter> specifications, if present, is a policy filter. A router chooses a default router from the routes in its routing table that matches this <filter>.
In the following example, AS1 defaults to AS2 for routing.
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aut-num: AS1 default: to AS2
In the following example, router 7.7.7.1 in AS1 defaults to router 7.7.7.2 in AS2.
aut-num: AS1 default: to AS2 7.7.7.2 at 7.7.7.1
In the following example, AS1 defaults to AS2 and AS3, but prefers AS2 over AS3.
aut-num: AS1 default: to AS2 action pref = 1; default: to AS3 action pref = 2;
In the following example, AS1 defaults to AS2 and uses 128.9.0.0/16 as the default network.
aut-num: AS1 default: to AS2 networks { 128.9.0.0/16 }
Please note the semicolon at the end of an <import-factor>. If the policy specification is not structured (as in all the examples in other sections), this semicolon is optional. The syntax and semantics for an <import-factor> is already defined in Section 6.1.
An <import-term> is either a sequence of <import-factor>'s enclosed within matching braces (i.e. `{' and `}') or just a single <import- factor>. The semantics of an <import-term> is the union of <import- factor>'s using the specification order rule. An <import-expression> is either a single <import-term> or an <import-term> followed by one of the keywords "except" and "refine", followed by another <import- expression>. Note that our definition allows nested expressions. Hence there can be exceptions to exceptions, refinements to refinements, or even refinements to exceptions, and so on.
The semantics for the except operator is as follows: The result of an except operation is another <import-term>. The resulting policy set contains the policies of the right hand side but their filters are modified to only include the routes also matched by the left hand side. The policies of the left hand side are included afterwards and their filters are modified to exclude the routes matched by the right hand side. Please note that the filters are modified during this process but the actions are copied verbatim. When there are multiple levels of nesting, the operations (both except and refine) are performed right to left.
where the route 128.9.0.0/16 is originated by AS226, and AS226 is a member of the as set as-foo. In this example, the route 128.9.0.0/16 is accepted from AS3, any other route (not 128.9.0.0/16) originated by AS226 is accepted from AS2, and any other ASes' routes in as-foo is accepted from AS1.
We can come to the same conclusion using the algebra defined above. Consider the inner exception specification:
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from AS2 action pref = 2; accept AS226; except { from AS3 action pref = 3; accept {128.9.0.0/16}; }
is equivalent to
{ from AS3 action pref = 3; accept AS226 AND {128.9.0.0/16}; from AS2 action pref = 2; accept AS226 AND NOT {128.9.0.0/16}; }
Hence, the original expression is equivalent to:
import: from AS1 action pref = 1; accept as-foo; except { from AS3 action pref = 3; accept AS226 AND {128.9.0.0/16}; from AS2 action pref = 2; accept AS226 AND NOT {128.9.0.0/16}; }
which is equivalent to
import: { from AS3 action pref = 3; accept as-foo AND AS226 AND {128.9.0.0/16}; from AS2 action pref = 2; accept as-foo AND AS226 AND NOT {128.9.0.0/16}; from AS1 action pref = 1; accept as-foo AND NOT (AS226 AND NOT {128.9.0.0/16} OR AS226 AND {128.9.0.0/16}); }
Since AS226 is in as-foo and 128.9.0.0/16 is in AS226, it simplifies to:
import: { from AS3 action pref = 3; accept {128.9.0.0/16}; from AS2 action pref = 2; accept AS226 AND NOT {128.9.0.0/16}; from AS1 action pref = 1; accept as-foo AND NOT AS226; }
In the case of the refine operator, the resulting set is constructed by taking the cartasian product of the two sides as follows: for each policy l in the left hand side and for each policy r in the right hand side, the peerings of the resulting policy are the peerings
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common to both r and l; the filter of the resulting policy is the intersection of l's filter and r's filter; and action of the resulting policy is l's action followed by r's action. If there are no common peerings, or if the intersection of filters is empty, a resulting policy is not generated.
Consider the following example:
import: { from AS-ANY action pref = 1; accept community.contains({3560,10}); from AS-ANY action pref = 2; accept community.contains({3560,20}); } refine { from AS1 accept AS1; from AS2 accept AS2; from AS3 accept AS3; }
Here, any route with community {3560,10} is assigned a preference of 1 and any route with community {3560,20} is assigned a preference of 2 regardless of whom they are imported from. However, only AS1's routes are imported from AS1, and only AS2's routes are imported from AS2, and only AS3's routes are imported form AS3, and no routes are imported from any other AS. We can reach the same conclusion using the above algebra. That is, our example is equivalent to:
import: { from AS1 action pref = 1; accept community.contains({3560,10}) AND AS1; from AS1 action pref = 2; accept community.contains({3560,20}) AND AS1; from AS2 action pref = 1; accept community.contains({3560,10}) AND AS2; from AS2 action pref = 2; accept community.contains({3560,20}) AND AS2; from AS3 action pref = 1; accept community.contains({3560,10}) AND AS3; from AS3 action pref = 2; accept community.contains({3560,20}) AND AS3; }
Note that the common peerings between "from AS1" and "from AS-ANY" are those peerings in "from AS1". Even though we do not formally define "common peerings", it is straight forward to deduce the definition from the definitions of peerings (please see Section 6.1.1).
Consider the following example:
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import: { from AS-ANY action med = 0; accept {0.0.0.0/0^0-18}; } refine { from AS1 at 7.7.7.1 action pref = 1; accept AS1; from AS1 action pref = 2; accept AS1; }
where only routes of length 0 to 18 are accepted and med's value is set to 0 to disable med's effect for all peerings; In addition, from AS1 only AS1's routes are imported, and AS1's routes imported at 7.7.7.1 are preferred over other peerings. This is equivalent to:
import: { from AS1 at 7.7.7.1 action med=0; pref=1; accept {0.0.0.0/0^0-18} AND AS1; from AS1 action med=0; pref=2; accept {0.0.0.0/0^0-18} AND AS1;
The above syntax and semantics also apply equally to structured export policies with "from" replaced with "to" and "accept" is replaced with "announce".
The dictionary class provides extensibility to RPSL. Dictionary objects define routing policy attributes, types, and routing protocols. Routing policy attributes, henceforth called rp- attributes, may correspond to actual protocol attributes, such as the BGP path attributes (e.g. community, dpa, and AS-path), or they may correspond to router features (e.g. BGP route flap damping). As new protocols, new protocol attributes, or new router features are introduced, the dictionary object is updated to include appropriate rp-attribute and protocol definitions.
An rp-attribute is an abstract class; that is a data representation is not available. Instead, they are accessed through access methods. For example, the rp-attribute for the BGP AS-path attribute is called aspath; and it has an access method called prepend which stuffs extra AS numbers to the AS-path attributes. Access methods can take arguments. Arguments are strongly typed. For example, the method prepend above takes AS numbers as argument.
Once an rp-attribute is defined in the dictionary, it can be used to describe policy filters and actions. Policy analysis tools are required to fetch the dictionary object and recognize newly defined rp-attributes, types, and protocols. The analysis tools may approximate policy analyses on rp-attributes that they do not
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understand: a filter method may always match, and an action method may always perform no-operation. Analysis tools may even download code to perform appropriate operations using mechanisms outside the scope of RPSL.
We next describe the syntax and semantics of the dictionary class. This description is not essential for understanding dictionary objects (but it is essential for creating one). Please feel free to skip to the RPSL Initial Dictionary subsection (Section 7.1).
The attributes of the dictionary class are shown in Figure 18. The dictionary attribute is the name of the dictionary object, obeying the RPSL naming rules. There can be many dictionary objects, however there is always one well-known dictionary object "RPSL". All tools use this dictionary by default.
The rp-attribute attribute has the following syntax:
Attribute Value Type dictionary <object-name> mandatory, single-valued, class key rp-attribute see description in text optional, multi valued typedef see description in text optional, multi valued protocol see description in text optional, multi valued
where <name> is the name of the rp-attribute; and <method-i> is the name of an access method for the rp-attribute, taking Ni arguments where the j-th argument is of type <type-i-j>. A method name is either an RPSL name or one of the operators defined in Figure 19. The operator methods with the exception of operator() and operator[] can take only one argument.
An rp-attribute can have many methods defined for it. Some of the methods may even have the same name, in which case their arguments are of different types. If the argument list is followed by "...", the method takes a variable number of arguments. In this case, the actual arguments after the Nth argument are of type <type-N>.
Arguments are strongly typed. A type of an argument can be one of the predefined types or one of the dictionary defined types. The predefined type names are listed in Figure 20. The integer and the real types can be followed by a lower and an upper bound to specify the set of valid values of the argument. The range specification is optional. We use the ANSI C language conventions for representing integer, real and string values. The enum type is followed by a list of RPSL names which are the valid values of the type. The boolean type can take the values true or false. as_number, ipv4_address, address_prefix and dns_name types are as in Section 2. filter type is a policy filter as in Section 6.
The typedef attribute specifies a dictionary defined type. Its syntax is as follows:
typedef: <name> union <type-1>, ... , <type-N> | <name> list [<min_elems>:<max_elems>] of <type>
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where <name> is the name of the type being defined and <type-M> is another type name, either predefined or dictionary defined. In the first form, the type defined is either of the types <type-1> through <type-N> (analogous to unions in C[12]). In the second form, the type defined is a list type where the list elements are of <type> and the list contains at least <min_elems> and at most <max_elems> elements. The size specification is optional. In this case, there is no restriction in the number of list elements. A value of a list type is represented as a sequence of elements separated by the character "," and enclosed by the characters "{" and "}".
A protocol attribute of the dictionary class defines a protocol and a set of peering options for that protocol (which are used in inet-rtr class in Section 9). Its syntax is as follows:
where <name> is the name of the protocol; MANDATORY and OPTIONAL are keywords; and <option-i> is a peering option for this protocol, taking Ni many arguments. The syntax and semantics of the arguments are as in the rp-attribute. If the keyword MANDATORY is used the option is mandatory and needs to be specified for each peering of this protocol. If the keyword OPTIONAL is used the option can be skipped.
7.1 Initial RPSL Dictionary and Example Policy Actions and Filters
dictionary: RPSL rp-attribute: # preference, smaller values represent higher preferences pref operator=(integer[0, 65535]) rp-attribute: # BGP multi_exit_discriminator attribute med operator=(integer[0, 65535]) # to set med to the IGP metric: med = igp_cost; operator=(enum[igp_cost]) rp-attribute: # BGP destination preference attribute (dpa) dpa operator=(integer[0, 65535]) rp-attribute: # BGP aspath attribute aspath # prepends AS numbers from last to first order prepend(as_number, ...)
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typedef: # a community value in RPSL is either # - a 4 byte integer # - internet, no_export, no_advertise (see RFC-1997) # - two 2-byte integers to be concatanated eg. {3561,70} community_elm union integer[1, 4294967200], enum[internet, no_export, no_advertise], list[2:2] of integer[0, 65535] typedef: # list of community values { 40, no_export, {3561,70}} community_list list of community_elm rp-attribute: # BGP community attribute community # set to a list of communities operator=(community_list) # order independent equality comparison operator==(community_list) # append community values operator.=(community_elm) append(community_elm, ...) # delete community values delete(community_elm, ...) # a filter: true if one of community values is contained contains(community_elm, ...) # shortcut to contains: community(no_export, {3561,70}) operator()(community_elm, ...) rp-attribute: # next hop router in a static route next-hop operator=(ipv4_address) # a router address operator=(enum[self]) # router's own address rp-attribute: # cost of a static route cost operator=(integer[0, 65535]) protocol: BGP4 # as number of the peer router MANDATORY asno(as_number) # enable flap damping OPTIONAL flap_damp() OPTIONAL flap_damp(integer[0,65535],# penalty per flap integer[0,65535], # penalty value for supression integer[0,65535],# penalty value for reuse integer[0,65535],# halflife in secs when up integer[0,65535], # halflife in secs when down integer[0,65535])# maximum penalty
Figure 21 shows the initial RPSL dictionary. It has seven rp- attributes: pref to assign local preference to the routes accepted; med to assign a value to the MULTI_EXIT_DISCRIMINATOR BGP attribute; dpa to assign a value to the DPA BGP attribute; aspath to prepend a value to the AS_PATH BGP attribute; community to assign a value to or to check the value of the community BGP attribute; next-hop to assign next hop routers to static routes; and cost to assign a cost to static routes. The dictionary defines two types: community_elm and community_list. community_elm type is either a 4-byte unsigned integer, or one of the keywords no_export or no_advertise (defined in [7]), or a list of two 2-byte unsigned integers in which case the two integers are concatenated to form a 4-byte integer. (The last form is often used in the Internet to partition the community number space. A provider uses its AS number as the first two bytes, and assigns a semantics of its choice to the last two bytes.)
The initial dictionary (Figure 21) defines only options for the Border Gateway Protocol: asno and flap_damp. The mandatory asno option is the AS number of the peer router. The optional flap_damp option instructs the router to damp route flaps[19] when importing routes from the peer router.
It can be specified with or without parameters. If parameters are missing, they default to:
flap_damp(1000, 2000, 750, 900, 900, 20000)
That is, a penalty of 1000 is assigned at each route flap, the route is suppressed when penalty reaches 2000. The penalty is reduced in half after 15 minutes (900 seconds) of stability regardless of whether the route is up or down. A supressed route is reused when the penalty falls below 750. The maximum penalty a route can be
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assigned is 20,000 (i.e. the maximum suppress time after a route becomes stable is about 75 minutes). These parameters are consistent with the default flap damping parameters in several routers.
Policy Actions and Filters Using RP-Attributes
The syntax of a policy action or a filter using an rp-attribute x is as follows:
x.method(arguments) x "op" argument
where method is a method and "op" is an operator method of the rp- attribute x. If an operator method is used in specifying a composite policy filter, it evaluates earlier than the composite policy filter operators (i.e. AND, OR, NOT, and implicit or operator).
The pref rp-attribute can be assigned a positive integer as follows:
pref = 10;
The med rp-attribute can be assigned either a positive integer or the word "igp_cost" as follows:
med = 0; med = igp_cost;
The dpa rp-attribute can be assigned a positive integer as follows:
dpa = 100;
The BGP community attribute is list-valued, that is it is a list of 4-byte integers each representing a "community". The following examples demonstrate how to add communities to this rp-attribute:
community .= 100; community .= NO_EXPORT; community .= {3561,10};
In the last case, a 4-byte integer is constructed where the more significant two bytes equal 3561 and the less significant two bytes equal 10. The following examples demonstrate how to delete communities from the community rp-attribute:
community.delete(100, NO_EXPORT, {3561,10});
Filters that use the community rp-attribute can be defined as demonstrated by the following examples:
The community rp-attribute can be set to a list of communities as follows:
community = {100, NO_EXPORT, {3561,10}, 200}; community = {};
In this first case, the community rp-attribute contains the communities 100, NO_EXPORT, {3561,10}, and 200. In the latter case, the community rp-attribute is cleared. The community rp-attribute can be compared against a list of communities as follows:
community == {100, NO_EXPORT, {3561,10}, 200}; # exact match
To influence the route selection, the BGP as_path rp-attribute can be made longer by prepending AS numbers to it as follows:
med = -50; # -50 is not in the range med = igp; # igp is not one of the enum values med.assign(10); # method assign is not defined community.append({AS3561,20}); # the first argument should be 3561
Figure 22 shows a more advanced example using the rp-attribute community. In this example, AS3561 bases its route selection preference on the community attribute. Other ASes may indirectly affect AS3561's route selection by including the appropriate communities in their route announcements.
aut-num: AS1 export: to AS2 action community.={3561,90}; to AS3 action community.={3561,80}; announce AS1
The components, aggr-bndry, aggr-mtd, export-comps, inject, and holes attributes are used for specifying aggregate routes [9]. A route object specifies an aggregate route if any of these attributes, with the exception of inject, is specified. The origin attribute for an aggregate route is the AS performing the aggregation, i.e. the aggregator AS. In this section, we used the term "aggregate" to refer to the route generated, the term "component" to refer to the routes used to generate the path attributes of the aggregate, and the term "more specifics" to refer to any route which is a more specific of the aggregate regardless of whether it was used to form the path attributes.
The components attribute defines what component routes are used to form the aggregate. Its syntax is as follows:
where <protocol> is a routing protocol name such as BGP, OSPF or RIP (valid names are defined in the dictionary) and <filter> is a policy expression. The routes that match one of these filters and are learned from the corresponding protocol are used to form the aggregate. If <protocol> is omitted, it defaults to any protocol. <filter> implicitly contains an "AND" term with the more specifics of the aggregate so that only the component routes are selected. If the keyword ATOMIC is used, the aggregation is done atomically [9]. If a <filter> is not specified it defaults to more specifics. If the components attribute is missing, all more specifics without the ATOMIC keyword is used.
Figure 23 shows two route objects. In the first example, more specifics of 128.8.0.0/15 with AS paths starting with AS2 are aggregated. In the second example, some routes learned from BGP and some routes learned form OSPF are aggregated.
The aggr-bndry attribute is an expression over AS numbers and sets using operators AND, OR, and NOT. The result defines the set of ASes which form the aggregation boundary. If the aggr-bndry attribute is missing, the origin AS is the sole aggregation boundary. Outside the aggregation boundary, only the aggregate is exported and more specifics are suppressed. However, within the boundary, the more specifics are also exchanged.
The aggr-mtd attribute specifies how the aggregate is generated. Its syntax is as follow:
aggr-mtd: inbound | outbound [<as-expression>]
where <as-expression> is an expression over AS numbers and sets using operators AND, OR, and NOT. If <as-expression> is missing, it defaults to AS-ANY. If outbound aggregation is specified, the more specifics of the aggregate will be present within the AS and the aggregate will be formed at all inter-AS boundaries with ASes in <as-expression> before export, except for ASes that are within the aggregating boundary (i.e. aggr-bndry is enforced regardless of <as-expression>). If inbound aggregation is specified, the aggregate is formed at all inter-AS boundaries prior to importing routes into the aggregator AS. Note that <as-expression> can not be specified with inbound aggregation. If aggr-mtd attribute is missing, it defaults to "outbound AS-ANY".
Figure 24 shows an example of an outbound aggregation. In this example, AS1 and AS2 are coordinating aggregation and announcing only the less specific 128.8.0.0/15 to outside world, but exchanging more specifics between each other. This form of aggregation is useful when some of the components are within AS1 and some are within AS2.
When a set of routes are aggregated, the intent is to export only the aggregate route and suppress exporting of the more specifics outside the aggregation boundary. However, to satisfy certain policy and topology constraints (e.g. a multi-homed component), it is often required to export some of the components. The export-comps attribute equals an RPSL filter that matches the more specifics that need to be exported outside the aggregation boundary. If this attribute is missing, more specifics are not exported outside the aggregation boundary. Note that, the export-comps filter contains an implicit "AND" term with the more specifics of the aggregate.
Figure 25 shows an example of an outbound aggregation. In this example, the more specific 128.8.8.0/24 is exported outside AS1 in addition to the aggregate. This is useful, when 128.8.8.0/24 is multi-homed site to AS1 with some other AS.
where <action> is an action specification (see Section 6.1.2), <condition> is a boolean expression described below, and<router- expression> is an expression over router IP addresses and DNS names using operators AND, OR, and NOT. The DNS name can only be used if there is an inet-rtr object for that name that binds the name to IP addresses.
All routers in <router-expression> and in the aggregator AS perform the aggregation. If a <router-expression> is not specified, all routers inside the aggregator AS perform the aggregation. The <action> specification may set path attributes of the aggregate, such as assign a preferences to the aggregate.
The upon clause is a boolean condition. The aggregate is generated if and only if this condition is true. <condition> is a boolean expression using the logical operators AND and OR (i.e. operator NOT is not allowed) over:
HAVE-COMPONENTS { list of prefixes } EXCLUDE { list of prefixes } STATIC
The list of prefixes in HAVE-COMPONENTS can only be more specifics of the aggregate. It evaluates to true when all the prefixes listed are present in the routing table of the aggregating router. The list can also include prefix ranges (i.e. using operators ^-, ^+, ^n, and ^n- m). In this case, at least one prefix from each prefix range needs to be present in the routing table for the condition to be true. The list of prefixes in EXCLUDE can be arbitrary. It evaluates to true when none of the prefixes listed is present in the routing table. The list can also include prefix ranges, and no prefix in that range should be present in the routing table. The keyword static always evaluates to true. If no upon clause is specified the aggregate is generated if an only if there is a component in the routing table (i.e. a more specific that matches the filter in the components attribute).
inject: upon HAVE-COMPONENTS {128.8.0.0/16, 128.9.0.0/16} holes: 128.8.8.0/24
Figure 26: Examples of inject.
Figure 26 shows two examples. In the first case, the aggregate is injected at two routers each one setting the dpa path attribute differently. In the second case, the aggregate is generated only if both 128.8.0.0/16 and 128.9.0.0/16 are present in the routing table, as opposed to the first case where the presence of just one of them is sufficient for injection.
The holes attribute lists the component address prefixes which are not reachable through the aggregate route (perhaps that part of the address space is unallocated). The holes attribute is useful for diagnosis purposes. In Figure 26, the second example has a hole, namely 128.8.8.0/24. This may be due to a customer changing providers and taking this part of the address space with it.
An aggregate formed is announced to other ASes only if the export policies of the AS allows exporting the aggregate. When the aggregate is formed, the more specifics are suppressed from being exported except to the ASes in aggr-bndry and except the components in export-comps. For such exceptions to happen, the export policies of the AS should explicitly allow exporting of these exceptions.
If an aggregate is not formed (due to the upon clause), then the more specifics of the aggregate can be exported to other ASes, but only if the export policies of the AS allows it. In other words, before a route (aggregate or more specific) is exported it is filtered twice, once based on the route objects, and once based on the export policies of the AS.
route: 128.8.0.0/16 origin: AS1
route: 128.9.0.0/16 origin: AS1
route: 128.8.0.0/15 origin: AS1 aggr-bndry: AS1 or AS2 or AS3 aggr-mtd: outbound AS3 or AS4 or AS5 components: {128.8.0.0/16, 128.9.0.0/16} inject: upon HAVE-COMPONENTS {128.9.0.0/16, 128.8.0.0/16}
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aut-num: AS1 export: to AS2 announce AS1 export: to AS3 announce AS1 and not {128.9.0.0/16} export: to AS4 announce AS1 export: to AS5 announce AS1 export: to AS6 announce AS1
Figure 27: Interaction with policies in aut-num class.
In Figure 27 shows an interaction example. By examining the route objects, the more specifics 128.8.0.0/16 and 128.9.0.0/16 should be exchanged between AS1, AS2 and AS3 (i.e. the aggregation boundary). Outbound aggregation is done to AS4 and AS5 and not to AS3, since AS3 is in the aggregation boundary. The aut-num object allows exporting both components to AS2, but only the component 128.8.0.0/16 to AS3. The aggregate can only be formed if both components are available. In this case, only the aggregate is announced to AS4 and AS5. However, if one of the components is not available the aggregate will not be formed, and any available component or more specific will be exported to AS4 and AS5. Regardless of aggregation is performed or not, only the more specifics will be exported to AS6 (it is not listed in the aggr-mtd attribute).
When doing an inbound aggregation, configuration generators may eliminating the aggregation statements on routers where import policy of the AS prohibits importing of any more specifics.
8.1.2 Ambiguity resolution with overlapping aggregates
When several aggregate routes are specified and they overlap, i.e. one is less specific of the other, they must be evaluated more specific to less specific order. When an aggregation is performed, the aggregate and the components listed in the export-comps attribute are available for generating the next less specific aggregate. The components that are not specified in the export-comps attribute are not available. A route is exportable to an AS if it is the least specific aggregate exportable to that AS or it is listed in the export-comps attribute of an exportable route. Note that this is a recursive definition.
route: 128.8.0.0/15 origin: AS1 aggr-bndry: AS1 or AS2 aggr-mtd: outbound inject: upon HAVE-COMPONENTS {128.8.0.0/16, 128.9.0.0/16}
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route: 128.10.0.0/15 origin: AS1 aggr-bndry: AS1 or AS3 aggr-mtd: outbound inject: upon HAVE-COMPONENTS {128.10.0.0/16, 128.11.0.0/16} export-comps: {128.11.0.0/16}
route: 128.8.0.0/14 origin: AS1 aggr-bndry: AS1 or AS2 or AS3 aggr-mtd: outbound inject: upon HAVE-COMPONENTS {128.8.0.0/15, 128.10.0.0/15} export-comps: {128.10.0.0/15}
Figure 28: Overlapping aggregations.
In Figure 28, AS1 together with AS2 aggregates 128.8.0.0/16 and 128.9.0.0/16 into 128.8.0.0/15. Together with AS3, AS1 aggregates 128.10.0.0/16 and 128.11.0.0/16 into 128.10.0.0/15. But altogether they aggregate these four routes into 128.8.0.0/14. Assuming all four components are available, a router in AS1 for an outside AS, say AS4, will first generate 128.8.0.0/15 and 128.10.0.0/15. This will make 128.8.0.0/15, 128.10.0.0/15 and its exception 128.11.0.0/16 available for generating 128.8.0.0/14. The router will then generate 128.8.0.0/14 from these three routes. Hence for AS4, 128.8.0.0/14 and its exception 128.10.0.0/15 and its exception 128.11.0.0/16 will be exportable.
For AS2, a router in AS1 will only generate 128.10.0.0/15. Hence, 128.10.0.0/15 and its exception 128.11.0.0/16 will be exportable. Note that 128.8.0.0/16 and 128.9.0.0/16 are also exportable since they did not participate in an aggregate exportable to AS2.
Similarly, for AS3, a router in AS1 will only generate 128.8.0.0/15. In this case 128.8.0.0/15, 128.10.0.0/16, 128.11.0.0/16 are exportable.
The inject attribute can be used to specify static routes by using "upon static" as the condition:
inject: [at <router>] ... [action <action>] upon static
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In this case, the <router> executes the <action> and injects the route to the interAS routing system statically. <action> may set certain route attributes such as a next-hop router or a cost.
In the following example, the router 7.7.7.1 injects the route 128.7.0.0/16. The next-hop routers (in this example, there are two next-hop routers) for this route are 7.7.7.2 and 7.7.7.3 and the route has a cost of 10 over 7.7.7.2 and 20 over 7.7.7.3.
route: 128.7.0.0/16 origin: AS1 inject: at 7.7.7.1 action next-hop = 7.7.7.2; cost = 10; upon static inject: at 7.7.7.1 action next-hop = 7.7.7.3; cost = 20; upon static
Routers are specified using the inet-rtr class. The attributes of the inet-rtr class are shown in Figure 29. The inet-rtr attribute is a valid DNS name of the router described. Each alias attribute, if present, is a canonical DNS name for the router. The local-as attribute specifies the AS number of the AS which owns/operates this router.
Attribute Value Type inet-rtr <dns-name> mandatory, single-valued, class key alias <dns-name> optional, multi-valued local-as <as-number> mandatory, single-valued ifaddr see description in text mandatory, multi-valued peer see description in text optional, multi-valued
Figure 29: inet-rtr Class Attributes
The value of an ifaddr attribute has the following syntax:
The IP address and the mask length are mandatory for each interface. Optionally an action can be specified to set other parameters of this interface.
Figure 30 presents an example inet-rtr object. The name of the router is "amsterdam.ripe.net". "amsterdam1.ripe.net" is a canonical name for the router. The router is connected to 4 networks. Its IP addresses and mask lengths in those networks are specified in the ifaddr attributes.
Each peer attribute, if present, specifies a protocol peering with another router. The value of a peer attribute has the following syntax:
<protocol> <ipv4-address> <options>
where <protocol> is a protocol name, <ipv4-address> is the IP address of the peer router, and <options> is a comma separated list of peering options for <protocol>. Possible protocol names and attributes are defined in the dictionary (please see Section 7). In the above example, the router has a BGP peering with the router 192.87.45.195 in AS3334 and turns the flap damping on when importing routes from this router.
This document describes RPSL, a language for expressing routing policies. The language defines a maintainer (mntner class) object which is the entity which controls or "maintains" the objects stored in a database expressed by RPSL. Requests from maintainers can be authenticated with various techniques as defined by the "auth" attribute of the maintainer object.
The exact protocols used by IRR's to communicate RPSL objects is beyond the scope of this document, but it is envisioned that several techniques may be used, ranging from interactive query/update protocols to store and forward protocols similar to or based on electronic mail (or even voice telephone calls). Regardless of which protocols are used in a given situation, it is expected that appropriate security techniques such as IPSEC, TLS or PGP/MIME will be utilized.
We would like to thank Jessica Yu, Randy Bush, Alan Barrett, David Kessens, Bill Manning, Sue Hares, Ramesh Govindan, Kannan Varadhan, Satish Kumar, Craig Labovitz, Rusty Eddy, David J. LeRoy, David Whipple, Jon Postel, Deborah Estrin, Elliot Schwartz, Joachim Schmitz, Mark Prior, Tony Przygienda, David Woodgate, and the participants of the IETF RPS Working Group for various comments and suggestions.
[2] Alaettinouglu, C., Meyer, D., and J. Schmitz, "Application of Routing Policy Specification Language (RPSL) on the Internet", Work in Progress.
[3] T. Bates. Specifying an `Internet Router' in the Routing Registry. Technical Report RIPE-122, RIPE, RIPE NCC, Amsterdam, Netherlands, October 1994.
[4] T. Bates, E. Gerich, L. Joncheray, J-M. Jouanigot, D. Karrenberg, M. Terpstra, and J. Yu. Representation of IP Routing Policies in a Routing Registry. Technical Report ripe- 181, RIPE, RIPE NCC, Amsterdam, Netherlands, October 1994.
[5] Bates, T., Gerich, E., Joncheray, L., Jouanigot, J.M., Karrenberg, D., Terpstra, M., and J. Yu, "Representation of IP Routing Policies in a Routing Registry," RFC 1786, March 1995.
[6] T. Bates, J-M. Jouanigot, D. Karrenberg, P. Lothberg, and M. Terpstra. Representation of IP Routing Policies in the RIPE Database. Technical Report ripe-81, RIPE, RIPE NCC, Amsterdam, Netherlands, February 1993.
[7] Chandra, R., Traina, P., and T. Li, "BGP Communities Attribute," RFC 1997, August 1996.
[8] Crocker, D., "Standard for the format of ARPA Internet text messages, STD 11, RFC 822, August 1982.
[9] V. Fuller, T. Li, J. Yu, and K. Varadhan. Classless Inter- Domain Routing (CIDR): an Address Assignment and Aggregation Strategy, 1993.
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[10] D. Karrenberg and T. Bates. Description of Inter-AS Networks in the RIPE Routing Registry. Technical Report RIPE-104, RIPE, RIPE NCC, Amsterdam, Netherlands, December 1993.
[11] D. Karrenberg and M. Terpstra. Authorisation and Notification of Changes in the RIPE Database. Technical Report ripe-120, RIPE, RIPE NCC, Amsterdam, Netherlands, October 1994.
[12] B. W. Kernighan and D. M. Ritchie. The C Programming Language. Prentice-Hall, 1978.
[13] Kessens, D., Woeber, W., and D. Conrad, "RIDE referencing", Work in Progress.
[14] A. Lord and M. Terpstra. RIPE Database Template for Networks and Persons. Technical Report ripe-119, RIPE, RIPE NCC, Amsterdam, Netherlands, October 1994.
[15] A. M. R. Magee. RIPE NCC Database Documentation. Technical Report RIPE-157, RIPE, RIPE NCC, Amsterdam, Netherlands, May 1997.
[16] Mockapetris, P., "Domain names - concepts and facilities," STD 13, RFC 1034, November 1987.
[17] Y. Rekhter. Inter-Domain Routing Protocol (IDRP). Journal of Internetworking Research and Experience, 4:61--80, 1993.
[18] Rekhter, Y., and T. Li, "A Border Gateway Protocol 4 (BGP-4)," RFC 1771, March 1995.
[19] Villamizar, C., Chandra, R., and R. Govindan, "BGP Route Flap Damping", Work in Progress.
A Routing Registry Sites
The set of routing registries as of November 1996 are RIPE, RADB, CANet, MCI and ANS. You may contact one of these registries to find out the current list of registries.
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B Authors' Addresses
Cengiz Alaettinoglu USC Information Sciences Institute 4676 Admiralty Way, Suite 1001 Marina del Rey, CA 90292 EMail: cengiz@isi.edu
Tony Bates Cisco Systems, Inc. 170 West Tasman Drive San Jose, CA 95134 EMail: tbates@cisco.com
Elise Gerich At Home Network 385 Ravendale Drive Mountain View, CA 94043 EMail: epg@home.net
Daniel Karrenberg RIPE Network Coordination Centre (NCC) Kruislaan 409 NL-1098 SJ Amsterdam Netherlands EMail: dfk@ripe.net
David Meyer University of Oregon Eugene, OR 97403 EMail: meyer@antc.uoregon.edu
Marten Terpstra c/o Bay Networks, Inc. 2 Federal St Billerica MA 01821 EMail: marten@BayNetworks.com
Curtis Villamizar ANS EMail: curtis@ans.net
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C Full Copyright Statement
Copyright (C) The Internet Society (1998). All Rights Reserved.
This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English.
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This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.