Internet Engineering Task Force (IETF) D. Ma Request for Comments: 8416 ZDNS Category: Standards Track D. Mandelberg ISSN: 2070-1721 Unaffiliated T. Bruijnzeels NLnet Labs August 2018
Simplified Local Internet Number Resource Management with the RPKI (SLURM)
Abstract
The Resource Public Key Infrastructure (RPKI) is a global authorization infrastructure that allows the holder of Internet Number Resources (INRs) to make verifiable statements about those resources. Network operators, e.g., Internet Service Providers (ISPs), can use the RPKI to validate BGP route origin assertions. ISPs can also use the RPKI to validate the path of a BGP route. However, ISPs may want to establish a local view of exceptions to the RPKI data in the form of local filters and additions. The mechanisms described in this document provide a simple way to enable INR holders to establish a local, customized view of the RPKI, overriding global RPKI repository data as needed.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc8416.
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Copyright Notice
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The Resource Public Key Infrastructure (RPKI) is a global authorization infrastructure that allows the holder of Internet Number Resources (INRs) to make verifiable statements about those resources. For example, the holder of a block of IP(v4 or v6) addresses can issue a Route Origin Authorization (ROA) [RFC6482] to authorize an Autonomous System (AS) to originate routes for that block. Internet Service Providers (ISPs) can then use the RPKI to validate BGP routes. (Validation of the origin of a route is described in [RFC6811], and validation of the path of a route is described in [RFC8205].)
However, an RPKI Relying Party (RP) may want to override some of the information expressed via configured Trust Anchors (TAs) and the certificates downloaded from the RPKI repository system. For instance, [RFC6491] recommends the creation of ROAs that would invalidate public routes for reserved and unallocated address space, yet some ISPs might like to use BGP and the RPKI with private address space (see [RFC1918], [RFC4193], and [RFC6598]) or private AS numbers (see [RFC1930] and [RFC6996]). Local use of private address space and/or AS numbers is consistent with the RFCs cited above, but such use cannot be verified by the global RPKI. This motivates creation of mechanisms that enable a network operator to publish, at its discretion, an exception to the RPKI in the form of filters and additions (for its own use and that of its customers). Additionally, a network operator might wish to make use of a local override capability to protect routes from adverse actions [RFC8211], until the results of such actions have been addressed. The mechanisms developed to provide this capability to network operators are hereby called "Simplified Local Internet Number Resource Management with the RPKI (SLURM)".
SLURM allows an operator to create a local view of the global RPKI by generating sets of assertions. For origin validation [RFC6811], an assertion is a tuple of {IP prefix, prefix length, maximum length, Autonomous System Number (ASN)} as used by the RPKI-Router protocol, version 0 [RFC6810] and version 1 [RFC8210]. For BGPsec [RFC8205], an assertion is a tuple of {ASN, subject key identifier, router public key} as used by version 1 of the RPKI-Router protocol. (For the remainder of this document, these assertions are called "ROA Prefix Assertions" and "BGPsec Assertions", respectively.)
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.
SLURM provides a simple way to enable an RP to establish a local, customized view of the RPKI, overriding RPKI repository data if needed. To that end, an RP with SLURM filters out (i.e., removes from consideration for routing decisions) any assertions in the RPKI that are overridden by local ROA Prefix Assertions and BGPsec Assertions.
In general, the primary output of an RP is the data it sends to routers over the RPKI-Router protocol [RFC8210]. The RPKI-Router protocol enables routers to query an RP for all assertions it knows about (Reset Query) or for an update of only the changes in assertions (Serial Query). The mechanisms specified in this document are to be applied to the result set for a Reset Query and to both the old and new sets that are compared for a Serial Query. RP software may modify other forms of output in comparable ways, but that is outside the scope of this document.
SLURM filters and assertions are specified in JSON format [RFC8259]. JSON members that are not defined here MUST NOT be used in SLURM files. An RP MUST consider any deviations from the specifications to be errors. Future additions to the specifications in this document MUST use an incremented value for the "slurmVersion" member.
A SLURM file consists of a single JSON object containing the following members:
o A "slurmVersion" member that MUST be set to 1, encoded as a number
o A "validationOutputFilters" member (Section 3.3), whose value is an object. The object MUST contain exactly two members:
* A "prefixFilters" member, whose value is described in Section 3.3.1.
* A "bgpsecFilters" member, whose value is described in Section 3.3.2.
o A "locallyAddedAssertions" member (Section 3.4), whose value is an object. The object MUST contain exactly two members:
* A "prefixAssertions" member, whose value is described in Section 3.4.1.
* A "bgpsecAssertions" member, whose value is described in Section 3.4.2.
In the envisioned typical use case, an RP uses both Validation Output Filters and Locally Added Assertions. In this case, the resulting assertions MUST be the same as if output filtering were performed before locally adding assertions; that is, Locally Added Assertions MUST NOT be removed by output filtering.
The following JSON structure with JSON members represents a SLURM file that has no filters or assertions:
The RP can configure zero or more Validated ROA Prefix Filters ("Prefix Filters" for short). Each Prefix Filter can contain either an IPv4 or IPv6 prefix and/or an ASN. It is RECOMMENDED that an explanatory comment is included with each Prefix Filter so that it can be shown to users of the RP software.
The above is expressed as a value of the "prefixFilters" member, as an array of zero or more objects. Each object MUST contain either 1) one of the following members or 2) one of each of the following members.
o A "prefix" member, whose value is a string representing either an IPv4 prefix (see Section 3.1 of [RFC4632]) or an IPv6 prefix (see [RFC5952]).
o An "asn" member, whose value is a number.
In addition, each object MAY contain one optional "comment" member, whose value is a string.
The following example JSON structure represents a "prefixFilters" member with an array of example objects for each use case listed above:
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"prefixFilters": [ { "prefix": "192.0.2.0/24", "comment": "All VRPs encompassed by prefix" }, { "asn": 64496, "comment": "All VRPs matching ASN" }, { "prefix": "198.51.100.0/24", "asn": 64497, "comment": "All VRPs encompassed by prefix, matching ASN" } ]
Figure 3: "prefixFilters" Examples
Any Validated ROA Payload (VRP) [RFC6811] that matches any configured Prefix Filter MUST be removed from the RP's output.
A VRP is considered to match with a Prefix Filter if one of the following cases applies:
1. If the Prefix Filter only contains an IPv4 or IPv6 prefix, the VRP is considered to match the filter if the VRP prefix is equal to or covered by the Prefix Filter prefix.
2. If the Prefix Filter only contains an ASN, the VRP is considered to match the filter if the VRP ASN matches the Prefix Filter ASN.
3. If the Prefix Filter contains both an IPv4 or IPv6 prefix and an ASN, the VRP is considered to match if the VRP prefix is equal to or covered by the Prefix Filter prefix and the VRP ASN matches the Prefix Filter ASN.
The RP can configure zero or more BGPsec Assertion Filters ("BGPsec Filters" for short). Each BGPsec Filter can contain an ASN and/or the Base64 [RFC4648] encoding of a Router Subject Key Identifier (SKI), as described in [RFC8209] and [RFC6487]. It is RECOMMENDED that an explanatory comment is also included with each BGPsec Filter, so that it can be shown to users of the RP software.
The above is expressed as a value of the "bgpsecFilters" member, as an array of zero or more objects. Each object MUST contain one of either, or one each of both following members:
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o An "asn" member, whose value is a number
o An "SKI" member, whose value is the Base64 encoding without trailing '=' (Section 5 of [RFC4648]) of the certificate's Subject Key Identifier as described in Section 4.8.2 of [RFC6487]. (This is the value of the ASN.1 OCTET STRING without the ASN.1 tag or length fields.)
In addition, each object MAY contain one optional "comment" member, whose value is a string.
The following example JSON structure represents a "bgpsecFilters" member with an array of example objects for each use case listed above:
"bgpsecFilters": [ { "asn": 64496, "comment": "All keys for ASN" }, { "SKI": "<Base 64 of some SKI>", "comment": "Key matching Router SKI" }, { "asn": 64497, "SKI": "<Base 64 of some SKI>", "comment": "Key for ASN 64497 matching Router SKI" } ]
Figure 4: "bgpsecFilters" Examples
Any BGPsec Assertion that matches any configured BGPsec Filter MUST be removed from the RP's output. A BGPsec Assertion is considered to match with a BGPsec Filter if one of the following cases applies:
1. If the BGPsec Filter only contains an ASN, a BGPsec Assertion is considered to match if the Assertion ASN matches the Filter ASN.
2. If the BGPsec Filter only contains an SKI, a BGPsec Assertion is considered to match if the Assertion Router SKI matches the Filter SKI.
3. If the BGPsec Filter contains both an ASN and a Router SKI, then a BGPsec Assertion is considered to match if both the Assertion ASN matches the Filter ASN and the Assertion Router SKI matches the Filter SKI.
Each RP is locally configured with a (possibly empty) array of ROA Prefix Assertions ("Prefix Assertions" for short). Each ROA Prefix Assertion MUST contain an IPv4 or IPv6 prefix and an ASN. It MAY include a value for the maximum length. It is RECOMMENDED that an explanatory comment is also included with each so that it can be shown to users of the RP software.
The above is expressed as a value of the "prefixAssertions" member, as an array of zero or more objects. Each object MUST contain one of each of the following members:
o A "prefix" member, whose value is a string representing either an IPv4 prefix (see Section 3.1 of [RFC4632]) or an IPv6 prefix (see [RFC5952]).
o An "asn" member, whose value is a number.
In addition, each object MAY contain one of each of the following members:
o A "maxPrefixLength" member, whose value is a number.
o A "comment" member, whose value is a string.
The following example JSON structure represents a "prefixAssertions" member with an array of example objects for each use case listed above:
"prefixAssertions": [ { "asn": 64496, "prefix": "198.51.100.0/24", "comment": "My other important route" }, { "asn": 64496, "prefix": "2001:DB8::/32", "maxPrefixLength": 48, "comment": "My other important de-aggregated routes" } ]
Figure 5: "prefixAssertions" Examples
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Note that the combination of the prefix, ASN, and optional maximum length describes a VRP as described in [RFC6811]. The RP MUST add all Prefix Assertions found this way to the VRP found through RPKI validation and ensure that it sends the complete set of Protocol Data Units (PDUs), excluding duplicates when using the RPKI-Router protocol (see Sections 5.6 and 5.7 of [RFC8210]).
Each RP is locally configured with a (possibly empty) array of BGPsec Assertions. Each BGPsec Assertion MUST contain an AS number, a Router SKI, and the router public key. It is RECOMMENDED that an explanatory comment is also included so that it can be shown to users of the RP software.
The above is expressed as a value of the "bgpsecAssertions" member, as an array of zero or more objects. Each object MUST contain one each of all of the following members:
o An "asn" member, whose value is a number.
o An "SKI" member, whose value is the Base64 encoding without trailing '=' (Section 5 of [RFC4648]) of the certificate's Subject Key Identifier as described in Section 4.8.2 of [RFC6487] (This is the value of the ASN.1 OCTET STRING without the ASN.1 tag or length fields.)
o A "routerPublicKey" member, whose value is the Base64 encoding without trailing '=' (Section 5 of [RFC4648]) of the equivalent to the subjectPublicKeyInfo value of the router certificate's public key, as described in [RFC8208]. This is the full ASN.1 DER encoding of the subjectPublicKeyInfo, including the ASN.1 tag and length values of the subjectPublicKeyInfo SEQUENCE.
The following example JSON structure represents a "bgpsecAssertions" member with one object as described above:
"bgpsecAssertions": [ { "asn": 64496, "SKI": "<some base64 SKI>", "routerPublicKey": "<some base64 public key>", "comment": "My known key for my important ASN" } ]
Figure 6: "bgpsecAssertions" Examples
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Note that a "bgpsecAssertions" member matches the syntax of the Router Key PDU described in Section 5.10 of [RFC8210]. Relying Parties MUST add any "bgpsecAssertions" member thus found to the set of Router Key PDUs, excluding duplicates, when using the RPKI-Router protocol [RFC8210].
3.5. Example of a SLURM File with Filters and Assertions
The following JSON structure represents an example of a SLURM file that uses all the elements described in the previous sections:
"asn": 64496, "prefix": "198.51.100.0/24", "comment": "My other important route" }, { "asn": 64496, "prefix": "2001:DB8::/32", "maxPrefixLength": 48, "comment": "My other important de-aggregated routes" } ], "bgpsecAssertions": [ { "asn": 64496, "comment" : "My known key for my important ASN", "SKI": "<some base64 SKI>", "routerPublicKey": "<some base64 public key>" } ] } }
To ensure local consistency, the effect of SLURM MUST be atomic. That is, the output of the RP either MUST be the same as if a SLURM file were not used or MUST reflect the entire SLURM configuration. For an example of why this is required, consider the case of two local routes for the same prefix but different origin ASNs. Both routes are configured with Locally Added Assertions. If neither addition occurs, then both routes could be in the NotFound state [RFC6811]. If both additions occur, then both routes would be in the Valid state. However, if one addition occurs and the other does not, then one could be Invalid while the other is Valid.
An implementation MAY support the concurrent use of multiple SLURM files. In this case, the resulting inputs to Validation Output Filters and Locally Added Assertions are the respective unions of the inputs from each file. The envisioned typical use case for multiple files is when the files have distinct scopes. For instance, operators of two distinct networks may resort to one RP system to frame routing decisions. As such, they probably deliver SLURM files to this RP independently. Before an RP configures SLURM files from different sources, it MUST make sure there is no internal conflict among the INR assertions in these SLURM files. To do so, the RP SHOULD check the entries of each SLURM file with regard to overlaps of the INR assertions and report errors to the sources that created the SLURM files in question. The RP gets multiple SLURM files as a set, and the whole set MUST be rejected in case of any overlaps among the SLURM files.
If a problem is detected with the INR assertions in these SLURM files, the RP MUST NOT use them and SHOULD issue a warning as error report in the following cases:
1. There may be conflicting changes to ROA Prefix Assertions if an IP address X and distinct SLURM files Y and Z exist such that X is contained by any prefix in any "prefixAssertions" or "prefixFilters" in file Y and X is contained by any prefix in any "prefixAssertions" or "prefixFilters" in file Z.
2. There may be conflicting changes to BGPsec Assertions if an ASN X and distinct SLURM files Y and Z exist such that X is used in any "bgpsecAssertions" or "bgpsecFilters" in file Y and X is used in any "bgpsecAssertions" or "bgpsecFilters" in file Z.
The mechanisms described in this document provide a network operator with additional ways to control use of RPKI data while preserving autonomy in address space and ASN management. These mechanisms are only applied locally; they do not influence how other network operators interpret RPKI data. Nonetheless, care should be taken in how these mechanisms are employed. Note that it also is possible to use SLURM to (locally) manipulate assertions about non-private INRs, e.g., allocated address space that is globally routed. For example, a SLURM file may be used to override RPKI data that a network operator believes has been corrupted by an adverse action. Network operators who elect to use SLURM in this fashion should use extreme caution.
The goal of the mechanisms described in this document is to enable an RP to create its own view of the RPKI, which is intrinsically a security function. An RP using a SLURM file is trusting the assertions made in that file. Errors in the SLURM file used by an RP can undermine the security offered to that RP by the RPKI. A SLURM file could declare as invalid ROAs that would otherwise be valid, and vice versa. As a result, an RP MUST carefully consider the security implications of the SLURM file being used, especially if the file is provided by a third party.
Additionally, each RP using SLURM MUST ensure the authenticity and integrity of any SLURM file that it uses. Initially, the SLURM file may be preconfigured out of band, but if the RP updates its SLURM file over the network, it MUST verify the authenticity and integrity of the updated SLURM file. The mechanism to update the SLURM file to guarantee authenticity and integrity is out of the scope of this document.
[RFC8211] Kent, S. and D. Ma, "Adverse Actions by a Certification Authority (CA) or Repository Manager in the Resource Public Key Infrastructure (RPKI)", RFC 8211, DOI 10.17487/RFC8211, September 2017, <https://www.rfc-editor.org/info/rfc8211>.
Acknowledgments
The authors would like to thank Stephen Kent for his guidance and detailed reviews of this document. The authors would also like to thank Richard Hansen for his careful reviews and Hui Zou and Chunlin An for their editorial assistance.
Authors' Addresses
Di Ma ZDNS 4 South 4th St. Zhongguancun Haidian, Beijing 100190 China