Network Working Group W. Sawyer Request for Comments: 4036 April 2005 Category: Standards Track
Management Information Base for Data Over Cable Service Interface Specification (DOCSIS) Cable Modem Termination Systems for Subscriber Management
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 (2005).
Abstract
This memo defines a portion of the Management Information Base (MIB) for use with network management protocols in the Internet community. In particular, it defines a set of managed objects for Simple Network Management Protocol (SNMP)-based management of Data-over-Cable Service Interface Specification (DOCSIS)-compliant Cable Modem Termination Systems. These managed objects facilitate protection of the cable network from misuse by subscribers. The Differentiated Services MIB (RFC 3289) provides the filtering functions needed here, making use of classification items defined in this specification.
Table of Contents
1. The Internet-Standard Management Framework.................... 2 2. Conventions................................................... 2 3. Overview...................................................... 2 3.1. Structure of the MIB.................................... 4 3.1.1. docsSubMgtFilterGroupTable...................... 4 3.1.2. IPv4 Compliance................................. 5 3.2. Management Requirements................................. 5 3.2.1. Interaction with DOCSIS Provisioning for CPE Address Control................................. 6 3.2.2. Interaction with DOCSIS Provisioning for Filtering....................................... 6 3.2.3. Distinguishing Modem from Subscriber Traffic.... 7
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3.3. Relationship to the Differentiated Services MIB [RFC3289]............................................... 7 3.3.1. Using the Filter Group to Extend Packet Classification.................................. 8 3.3.2. Interface Usage................................. 8 3.4. Filtering and the Tiny Fragment Attack.................. 9 4. Definitions................................................... 9 5. Acknowledgements.............................................. 23 6. IANA Considerations........................................... 23 7. Normative References.......................................... 23 8. Informative References........................................ 24 9. Security Considerations....................................... 25 Author's Address.................................................. 26 Full Copyright Statement.......................................... 27
For a detailed overview of the documents that describe the current Internet-Standard Management Framework, please refer to section 7 of RFC 3410 [RFC3410].
Managed objects are accessed via a virtual information store, termed the Management Information Base or MIB. MIB objects are generally accessed through the Simple Network Management Protocol (SNMP). Objects in the MIB are defined using the mechanisms defined in the Structure of Management Information (SMI). This memo specifies a MIB module that is compliant to the SMIv2, which is described in STD 58, RFC 2578 [RFC2578], STD 58, RFC 2579 [RFC2579] and STD 58, RFC 2580 [RFC2580].
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14, RFC 2119 [RFC2119].
This MIB module provides a set of objects required for the management of DOCSIS Cable Modem Termination Systems (CMTS). The specification is derived in part from the operational model described in the DOCSIS Radio Frequency Interface Specification [ITU-T-J122]. These managed objects facilitate protection of the cable network from misuse by subscribers. This misuse might include, for example, address spoofing, service spoofing, or operation of unauthorized services.
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The following figure illustrates the operational and physical deployment relationships between elements in a cable modem network. This MIB module resides at the CMTS, which is the first point in the public data network at which the cable operator controls physical access. The CMTS (possibly assisted by other IP service devices) acts as a network edge, separating the physical outside-plant cable television network from the operator's IP network.
| operator's IP network +------+ --------------------- | CMTS | operator's cable head-end +------+ --------------------- | +--------+--------+ CATV physical network | | | +----+ +----+ +----+ ------------------ | CM | | CM | | CM | subscriber premises +----+ +----+ +----+ ------------------ | | | subscriber host or network
This MIB module controls IP packet forwarding to and from each cable modem, at the CMTS. Different modems may be accorded different treatment.
Much of this module duplicates capabilities found in the DOCSIS Cable Device MIB [RFC2669]. Although it is expected that the Cable Device MIB will be used to prevent unwanted traffic from entering the cable network, it is also possible that a malicious user might tamper with cable modem software, disabling its filtering policies. This MIB provides a more secure mechanism, as physical access to the CMTS is controlled by the network operator.
In particular, this MIB provides two capabilities: first, to limit the IP addresses behind a modem, and second, to provide address and protocol filtering to and from a modem. The first duplicates the capabilities of the docsDevCpe group [RFC2669]. This provides for either learned or provisioned subscriber premises host IP addresses behind a cable modem.
The address and protocol filtering capability is similar to that performed by the cable modem itself. It differs in several respects because it is intended to control subscriber traffic at the CMTS, rather than at the individual CM. First, the MIB structure must be indexed appropriately at the CMTS to indicate which cable modem subscriber is intended. Second, rather than maintaining a separate list of filters for each modem at the CMTS, it is assumed that large numbers of modems will share filtering characteristics. Therefore, modems are grouped so as to share common filter lists.
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The filtering capability is implemented using the Classification, Counting, and Drop facilities of the Differentiated Services MIB [RFC3289]. In order to provide different filtering for various classes of subscribers, this MIB defines the docsSubMgtFilterGroupTable, which specifies which filters apply to each subscriber packet. This table is used by RFC 3289 as a first pass of classification, and also to choose a second pass of classification using the diffServMultiFieldClfrTable:
Because it is assumed that large numbers of modems will share filtering characteristics, DOCSIS signaling defines filter groups according to which cable modems share common filter lists. The operator creates references to these groups in the diffServClfrElementSpecific(1) entries above.
o The docsSubMgtCpeControlTable controls the acceptance of subscriber host addresses behind a cable modem.
o The docsSubMgtCpeIpTable monitors the subscriber host addresses that the CMTS believes exist behind the cable modem.
o The docsSubMgtCmFilterTable binds a cable modem to a set of filters in diffServMultiFieldClfrTable.
o The docsSubMgtFilterGroupTable provides the OIDs by which the diffServClfrElementTable selects a filter group.
The docsSubMgtCpeControlTable and docsSubMgtCmFilterTable AUGMENT the docsIfCmtsCmStatusTable from [RFC2670]. Similarly, docsSubMgtCpeIpTable expands this table (an additional index is used). As such, each entry in these tables is bound to a registered cable modem, as perceived by the CMTS.
The docsSubMgtFilterGroupTable links the filter group (signaled by DOCSIS as a small integer) to the diffServClfrElementEntry for the first pass of filter classification. diffServClfrElementSpecific
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requires a RowPointer. Thus, this table exists to provide referenced objects for diffServClfrElementSpecific. The classification method is as follows:
o Use the DOCSIS filter group, as inferred from the sending or receiving modem, as the classification criterion.
o Use docsSubMgtFilterGroupIndex as the value to match.
An entry exists in this Table if a reference to it exists in diffServClfrElementSpecific.
As such, contrary to common practice, the index for the table is read-only and is both the Entry's index and its only value.
Please note that the compliance statements in this version of the MIB module require support only for IPv4 addresses. That is because the current version of the DOCSIS protocols (1.0, 1.1, and 2.0) are not IPv6 capable. Although support for IPv6 will require changes to the DOCSIS protocols, it is expected that the only changes to the MIB module itself will be the addition of new compliance statements that mandate support for IPv6 addresses. All IP addresses that appear in this document conform to the textual conventions specified in [RFC4001].
The DOCSIS cable modem provisioning model [ITU-T-J122] requires that cable modems use TFTP to acquire a list of parameters. The modem then passes many of these parameters to the CMTS in the DOCSIS Registration message. The parameter values are digitally signed by the creator of the TFTP contents, and the signature is verified by the CMTS. In general, then, the CMTS itself need not be configured with the attributes of its cable modems. It will acquire these values through the Registration process that is secured by the digital signature.
Cable modem subscriber management, as described here, modifies this process slightly to reduce data and to ease administrative control. Filtering criteria, for example, are maintained through SNMP at the CMTS, and the modem registration merely signals the index values for the rows that apply to that modem.
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3.2.1. Interaction with DOCSIS Provisioning for CPE Address Control
The CMTS creates rows in docsSubMgtCpeControlTable for each modem as a result of the DOCSIS registration process. The DOCSIS registration attributes may include items semantically equivalent to those in the docsDevCpe section of the DOCSIS Cable Device MIB [RFC2669]:
o docsDevCpeEnroll o docsDevCpeIpMax o docsDevCpeIp
Successful DOCSIS registration will have the effect of setting the corresponding fields in the docsSubMgtCpeControlTable and the docsSubMgtCpeIpTable. If they are not present at modem registration, the CMTS shall apply the following:
o docsSubMgtCpeControlActive <-- docsSubMgtCpeActiveDefault o docsSubMgtCpeControlMaxCpeIp <-- docsSubMgtCpeMaxIpDefault o docsSubMgtCpeControlLearnable <-- docsSubMgtCpeLearnableDefault
Rows in docsSubMgtCpeIpTable are created through any of three ways: DOCSIS registration (as described above), learning by the CMTS, or some unspecified administrative mechanism on the CMTS. The docsDevCpeIpMax table bound applies only to the first two.
The CMTS may learn addresses simply by snooping source IP addresses from traffic originating from each cable modem. Other learning mechanisms (for example, ARP snooping) may be used. The learning mechanism is not defined by this document.
3.2.2. Interaction with DOCSIS Provisioning for Filtering
Rows in docsSubMgtCmFilterTable are created by the CMTS for each modem as a result of the DOCSIS registration process. The DOCSIS registration attributes may include four indices (see section C.1.1.18.3 of [ITU-T-J122]):
o One identifying the upstream (ingress with respect to the CMTS interface) filter group for packets originating from the cable modem (i.e., those packets whose source MAC address matches that of the cable modem).
o One identifying the upstream filter group for packets originating from subscribers attached to the cable modem (i.e., those packets whose source MAC address does not match that of the cable modem).
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o One identifying the downstream (egress with respect to the CMTS interface) filter group for packets destined to the cable modem (i.e., those packets whose destination MAC address matches that of the cable modem).
o One identifying the downstream filter group for packets destined to subscribers attached to the cable modem (i.e., those packets whose destination MAC address does not match that of the cable modem).
Successful registration will have the effect of setting docsSubMgtCmFilterCmDownstream, docsSubMgtCmFilterCmUpstream, docsSubMgtCmFilterSubDownstream, and docsSubMgtCmFilterSubUpstream, for that modem (just as if they were set through the SNMP protocol). If the DOCSIS attributes are not present, the four values are set to zero. The effect will be to use the default entry (diffServClfrElementSpecific=zeroDotZero) specified in the diffServClfrElementTable. Note that omission of the DOCSIS-signaled values results in application of the default filtering entry, not in omission of filtering.
3.2.3. Distinguishing Modem from Subscriber Traffic
All traffic originating from or destined to a subscriber site is potentially suspect and subject to suppression by the network operator. This is true even if the traffic is ostensibly sourced or sunk by the cable modem itself, rather than by the subscriber hosts behind the modem. To provide more nuanced administrative control, this document allows separate filter policies for modems and hosts. For example, modem policies may limit modems to server subnet - only access while allowing a different scope to subscribers.
The CMTS chooses the filter set to apply based solely on the MAC address (source MAC upstream, destination MAC downstream). If the MAC address matches that of the modem, then the docsSubMgtCmFilterCmUp/Downstream pair is used; otherwise, the docsSubMgtCmFilterSubUp/Downstream pair is applied.
If the CM acts as a router rather than as a DOCSIS bridging forwarder, then the network operator will only use the docsSubMgtCmFilterCmUp/Downstream pair.
3.3. Relationship to the Differentiated Services MIB [RFC3289]
DOCSIS CMTSes rely on the classification, counting, and drop facilities of the Differentiated Services MIB to screen subscriber packets for IP, TCP, and UDP characteristics. It is expected that
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any implementation of this MIB also includes at least the following from RFC 3289:
o diffServDataPathTable o diffServClfrTable o diffServClfrElementTable o diffServMultiFieldClfrTable o diffServActionTable o diffServCountActTable o diffServAlgDropTable (diffServAlgDropType=alwaysDrop)
The corresponding "next-free" objects are also required.
The use of other facilities from RFC 3289 is not precluded but is beyond the scope of this specification.
3.3.1. Using the Filter Group to Extend Packet Classification
The base capability of RFC 3289 assumes that all packets on the same direction of the same interface will be classified by the same criteria. Filter Groups, which are introduced in this document, expand on RFC 3289 to allow various subscribers to receive different classification (filtering) treatment. One way to view filter groups is as sub-interfaces within the physical DOCSIS channel. Another way to view them is as values of a field logically prepended to the packet prior to classification:
[filter group][DOCSIS MAC header][IP header]...
Of course this 'logical' field has no existence outside of the CMTS.
The diffServClfrTable and diffServClfrElementTable are then used twice: the first classifiers select among filter groups, using OIDs from docsSubMgtFilterGroupTable. The 'next' action on matching a filter group is to select a diffServClfrEntry that now classifies on IP/TCP/UDP criteria (the diffServMultiFieldClfrTable). The 'next' action on this second match may be a 'count' (and accept), a 'drop', or some other feature from RFC 3289.
For the purposes of DOCSIS subscriber management, only the DOCSIS MAC cable interface(s) are used. The interface appears as the index to diffServDataPathEntry, which is the starting point for diffserv MIB table traversal.
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The use of the diffserv MIB for other purposes, both on the DOCSIS MAC interfaces and on other network interfaces, is not precluded by this document.
It is recommended that the implementers prevent the "tiny fragment" and "overlapping fragment" attacks for the TCP filtering tables in this MIB, as discussed in RFC 1858 [RFC1858] and RFC 3128 [RFC3128].
Prevention of these attacks can be implemented with the following rules, when filtering is enabled:
o Admit all packets with fragment offset >= 2.
o Discard all packets with fragment offset = 1, or with fragment offset = 0 AND fragment payload length < 16.
o Apply filtering rules to all packets with fragment offset = 0.
docsSubMgt MODULE-IDENTITY LAST-UPDATED "200503290000Z" -- March 29, 2005 ORGANIZATION "IETF IP over Cable Data Network (IPCDN) Working Group" CONTACT-INFO " Wilson Sawyer Postal: 50 Kelly Brook Lane East Hampstead, NH 03826 U.S.A.
Phone: +1 603 382 7080 E-mail: wsawyer@ieee.org
IETF IPCDN Working Group General Discussion: ipcdn@ietf.org Subscribe: http://www.ietf.org/mailman/listinfo/ipcdn Archive: ftp://ftp.ietf.org/ietf-mail-archive/ipcdn Co-chairs: Richard Woundy, Richard_Woundy@cable.comcast.com Jean-Francois Mule, jf.mule@cablelabs.com" DESCRIPTION "This is the CMTS centric subscriber management MIB for DOCSIS-compliant CMTS. It provides the objects to allow a Cable Modem Termination operator to control the IP addresses and protocols associated with subscribers' cable modems.
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Copyright (C) The Internet Society (2005). This version of this MIB module is part of RFC 4036; see the RFC itself for full legal notices." REVISION "200503290000Z" -- March 29, 2005 DESCRIPTION "Initial version, published as RFC 4036. Note that the compliance statements in this version apply only to implementations that support DOCSIS 1.0/1.1/2.0, which are not IPv6-capable." ::= { mib-2 125 }
docsSubMgtCpeControlTable OBJECT-TYPE SYNTAX SEQUENCE OF DocsSubMgtCpeControlEntry MAX-ACCESS not-accessible STATUS current DESCRIPTION "This table AUGMENTs the docsIfCmtsCmStatusTable, adding four WRITEable objects, as well as a read-only object, all of which reflect the state of subscriber management on a particular CM." ::= { docsSubMgtObjects 1 }
docsSubMgtCpeControlEntry OBJECT-TYPE SYNTAX DocsSubMgtCpeControlEntry MAX-ACCESS not-accessible STATUS current DESCRIPTION "A row in the docsSubMgtCpeControlTable. All values are set at successful modem registration, either from the system default, or from objects included in the DOCSIS registration request sent upstream to the CMTS from the CM. The contents of this entry are meaningless unless the corresponding docsIfCmtsCmStatusValue (see reference) is registrationComplete(6). The persistence of this row is determined solely by the lifespan of the corresponding docsIfCmtsCmStatusEntry (normally StorageType=volatile)."
docsSubMgtCpeControlMaxCpeIp OBJECT-TYPE SYNTAX Integer32(0..2147483647) MAX-ACCESS read-write STATUS current DESCRIPTION "The number of simultaneous IP addresses permitted behind the CM. If this is set to zero, all CPE traffic from the CM is dropped. If the provisioning object corresponding to docsSubMgtCpeIpTable includes more CPE IP address entries for this modem than the value of this object, then this object is set to the count of the number of rows in docsSubMgtCpeIpTable that have the same docsIfCmtsCmStatusIndex value. (For example, if the CM has 5 IP addresses specified for it, this value is 5.) This limit applies to learned and DOCSIS-provisioned entries but not to entries added through some administrative process at the CMTS. If not set through DOCSIS provisioning, this object defaults to docsSubMgtCpeMaxIpDefault. Note that this object is only meaningful if docsSubMgtCpeControlActive is true." ::= { docsSubMgtCpeControlEntry 1 }
docsSubMgtCpeControlActive OBJECT-TYPE SYNTAX TruthValue MAX-ACCESS read-write STATUS current DESCRIPTION "Controls the application of subscriber management to this cable modem. If this is set to true, CMTS-based CPE control is active, and all the actions required by the various filter tables and controls apply at the CMTS. If this is set to false, no subscriber management filtering is done at the CMTS (but other filters may apply). If not set through DOCSIS provisioning, this object defaults to docsSubMgtCpeActiveDefault." ::= { docsSubMgtCpeControlEntry 2 }
docsSubMgtCpeControlLearnable OBJECT-TYPE SYNTAX TruthValue MAX-ACCESS read-write STATUS current DESCRIPTION "Controls whether the CMTS may learn (and pass traffic for) CPE IP addresses associated with a cable modem. If this is set to true, the CMTS may learn up to docsSubMgtMaxCpeIp
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addresses (less any DOCSIS-provisioned entries) related to this CM. Those IP addresses are added (by internal process) to the docsSubMgtCpeIpTable. The nature of the learning mechanism is not specified here.
If not set through DOCSIS provisioning, this object defaults to docsSubMgtCpeLearnableDefault. Note that this object is only meaningful if docsSubMgtCpeControlActive is true." ::= { docsSubMgtCpeControlEntry 3 }
docsSubMgtCpeControlReset OBJECT-TYPE SYNTAX TruthValue MAX-ACCESS read-write STATUS current DESCRIPTION "This object always returns false on read. If this object is set to true, the rows with 'learned' addresses in docsSubMgtCpeIpTable for this CM are deleted from that table." ::= { docsSubMgtCpeControlEntry 4 }
docsSubMgtCpeControlLastReset OBJECT-TYPE SYNTAX TimeStamp MAX-ACCESS read-only STATUS current DESCRIPTION "The value of sysUpTime when docsSubMgtCpeControlReset was last set true. Zero if never reset." DEFVAL { 0 } ::= { docsSubMgtCpeControlEntry 5 }
docsSubMgtCpeMaxIpDefault OBJECT-TYPE SYNTAX Integer32(0..2147483647) MAX-ACCESS read-write STATUS current DESCRIPTION "The default value for docsSubMgtCpeControlMaxCpeIp if not signaled in the DOCSIS Registration request. This value should be treated as nonvolatile; if set, its value should persist across device resets." DEFVAL { 16 } ::= { docsSubMgtObjects 2 }
docsSubMgtCpeActiveDefault OBJECT-TYPE SYNTAX TruthValue MAX-ACCESS read-write STATUS current DESCRIPTION "The default value for docsSubMgtCpeControlActive if not
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signaled in the DOCSIS Registration request. This value should be treated as nonvolatile; if set, its value should persist across device resets." DEFVAL { false } ::= { docsSubMgtObjects 3 }
docsSubMgtCpeLearnableDefault OBJECT-TYPE SYNTAX TruthValue MAX-ACCESS read-write STATUS current DESCRIPTION "The default value for docsSubMgtCpeControlLearnable if not signaled in the DOCSIS Registration request. This value should be treated as nonvolatile; if set, its value should persist across device resets." DEFVAL { true } ::= { docsSubMgtObjects 4 }
docsSubMgtCpeIpTable OBJECT-TYPE SYNTAX SEQUENCE OF DocsSubMgtCpeIpEntry MAX-ACCESS not-accessible STATUS current DESCRIPTION "A table of CPE IP addresses known on a per-CM basis." ::= { docsSubMgtObjects 5 }
docsSubMgtCpeIpEntry OBJECT-TYPE SYNTAX DocsSubMgtCpeIpEntry MAX-ACCESS not-accessible STATUS current DESCRIPTION "An entry in the docsSubMgtCpeIpTable. The first index is the specific modem we're referring to, and the second index is the specific CPE IP entry." INDEX { docsIfCmtsCmStatusIndex, docsSubMgtCpeIpIndex } ::= {docsSubMgtCpeIpTable 1 }
RFC 4036 DOCSIS Subscriber Management MIB April 2005
MAX-ACCESS not-accessible STATUS current DESCRIPTION "The index of this CPE IP address relative to the indexed CM. An entry is created either through the included CPE IP addresses in the provisioning object, or via learning.
If docsSubMgtCpeControlActive is true and a CMTS receives an IP packet from a CM that contains a source IP address that does not match one of the docsSubMgtCpeIpAddr entries for this CM, one of two things occurs. If the number of entries is less than docsSubMgtCpeControlMaxCpeIp, the source address is added to the table and the packet is forwarded. If the number of entries equals the docsSubMgtCpeControlMaxCpeIp, then the packet is dropped." ::= { docsSubMgtCpeIpEntry 1 }
docsSubMgtCpeIpAddressType OBJECT-TYPE SYNTAX InetAddressType MAX-ACCESS read-only STATUS current DESCRIPTION "The type of internet address of docsSubMgtCpeIpAddr." ::= { docsSubMgtCpeIpEntry 2 }
docsSubMgtCpeIpAddr OBJECT-TYPE SYNTAX InetAddress MAX-ACCESS read-only STATUS current DESCRIPTION "The IP address either set from provisioning or learned via address gleaning or other forwarding means. See docsSubMgtCpeIpIndex for the mechanism.
The type of this address is determined by the value of docsSubMgtCpeIpAddressType." ::= { docsSubMgtCpeIpEntry 3 }
docsSubMgtCpeIpLearned OBJECT-TYPE SYNTAX TruthValue MAX-ACCESS read-only STATUS current DESCRIPTION "If true, this entry was learned from IP packets sent upstream rather than from the provisioning objects." ::= { docsSubMgtCpeIpEntry 4 }
docsSubMgtCmFilterTable OBJECT-TYPE
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SYNTAX SEQUENCE OF DocsSubMgtCmFilterEntry MAX-ACCESS not-accessible STATUS current DESCRIPTION "Binds filter groups to modems, identifying for each modem the upstream and downstream filter groups that apply to packets for that modem. Normally, this table reflects the filter group values signaled by DOCSIS Registration, although values may be overridden by management action.
For each of the columns in this table, zero is a distinguished value, indicating that the default filtering action is to be taken rather than that associated with a filter group number. Zero is used if the filter group is not signaled by DOCSIS registration." ::= { docsSubMgtObjects 6 }
docsSubMgtCmFilterEntry OBJECT-TYPE SYNTAX DocsSubMgtCmFilterEntry MAX-ACCESS not-accessible STATUS current DESCRIPTION "Binds a filter group to each direction of traffic for a modem. The filters in this entry apply if docsSubMgtCpeControlActive is true.
The contents of this entry are meaningless unless the corresponding docsIfCmtsCmStatusValue (see reference) is registrationComplete(6). The persistence of this row is determined solely by the lifespan of the corresponding docsIfCmtsCmStatusEntry (normally StorageType=volatile)." REFERENCE "RFC 2670" AUGMENTS { docsIfCmtsCmStatusEntry } ::= {docsSubMgtCmFilterTable 1 }
docsSubMgtCmFilterSubDownstream OBJECT-TYPE SYNTAX Integer32(0..65535) MAX-ACCESS read-write STATUS current
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DESCRIPTION "The filter group applied to traffic destined for subscribers attached to the referenced CM. Upon row creation, this is set either to zero (use default classification, the diffServClfrElementSpecific=zeroDotZero row of diffServClfrElementTable) or to the value in the provisioning object sent upstream from the CM to the CMTS during registration. The value of this object is the same as that of the filter group index appearing as docsSubMgtFilterGroupIndex." ::= { docsSubMgtCmFilterEntry 1 }
docsSubMgtCmFilterSubUpstream OBJECT-TYPE SYNTAX Integer32(0..65535) MAX-ACCESS read-write STATUS current DESCRIPTION "The filter group applied to traffic originating from subscribers attached to the referenced CM. Upon row creation this is set to either zero (use default classification, the diffServClfrElementSpecific=zeroDotZero row of diffServClfrElementTable), or to the value in the provisioning object sent upstream from the CM to the CMTS. The value of this object is the same as that of the filter group index appearing as docsSubMgtFilterGroupIndex." ::= { docsSubMgtCmFilterEntry 2 }
docsSubMgtCmFilterCmDownstream OBJECT-TYPE SYNTAX Integer32(0..65535) MAX-ACCESS read-write STATUS current DESCRIPTION "The filter group applied to traffic destined for the referenced CM itself. Upon row creation this is set either to zero (use default classification, the diffServClfrElementSpecific=zeroDotZero row of diffServClfrElementTable), or to the value in the provisioning object sent upstream from the CM to the CMTS during registration. The value of this object is the same as that of the filter group index appearing as docsSubMgtFilterGroupIndex." ::= { docsSubMgtCmFilterEntry 3 }
docsSubMgtCmFilterCmUpstream OBJECT-TYPE SYNTAX Integer32(0..65535) MAX-ACCESS read-write STATUS current DESCRIPTION "The filter group applied to traffic originating from the referenced CM itself. This is set upon row creation to either
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zero (use default classification, the diffServClfrElementSpecific=zeroDotZero row of diffServClfrElementTable), or to the value in the provisioning object sent upstream from the CM to the CMTS during registration. The value of this object is the same as the filter group index appearing as docsSubMgtFilterGroupIndex." ::= { docsSubMgtCmFilterEntry 4 }
docsSubMgtFilterGroupTable OBJECT-TYPE SYNTAX SEQUENCE OF DocsSubMgtFilterGroupEntry MAX-ACCESS not-accessible STATUS current DESCRIPTION "Provides a collection of referenceable entries to which diffServClfrElementSpecific refers. This table provides filter group indices that can be compared with those signaled during DOCSIS registration. A packet matches an entry from this table if the packet originated from or is destined to a cable modem that registered this index as one of its four filter groups (see docsSubMgtCmFilterTable), and if the packet direction and MAC address select the use of this index among the four." ::= { docsSubMgtObjects 7 }
docsSubMgtFilterGroupEntry OBJECT-TYPE SYNTAX DocsSubMgtFilterGroupEntry MAX-ACCESS not-accessible STATUS current DESCRIPTION "An entry only exists if needed by the diffServClfrElementEntry. A packet matches this entry if the packet's cable modem registered this index as one of its four filter groups (see docsSubMgtCmFilterTable) and if the packet direction and MAC address select the use of this index among the four." INDEX { docsSubMgtFilterGroupIndex } ::= { docsSubMgtFilterGroupTable 1 }
docsSubMgtFilterGroupIndex OBJECT-TYPE SYNTAX Integer32(1..65535) MAX-ACCESS read-only STATUS current DESCRIPTION "The filter group index, from the set signaled at DOCSIS
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Registration. Provides a referenceable entry to which diffServClfrElementSpecific points. A packet matches this classifier entry if the packet's cable modem registered this index value as one of its four filter groups, and if the packet direction and MAC address select the use of this index among the four. Because this is the only field in this table, it is read-only, contrary to the usual SMI custom of making indices not-accessible.
Note that although zero may be signaled (or defaulted) at DOCSIS Registration to indicate a default filtering group, no such entry appears in this table, as diffServClfrElementSpecific will use a zeroDotZero pointer for that classification." ::= { docsSubMgtFilterGroupEntry 1 }
docsSubMgtBasicCompliance MODULE-COMPLIANCE STATUS current DESCRIPTION "The compliance statement for CMTS devices that implement CMTS centric subscriber management.
This compliance statement applies to implementations that support DOCSIS 1.0/1.1/2.0, which are not IPv6 capable."
OBJECT diffServDataPathStatus -- same as RFC3289 SYNTAX RowStatus { active(1) } WRITE-SYNTAX RowStatus { createAndGo(4), destroy(6) } DESCRIPTION "Support for createAndWait and notInService is not required."
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OBJECT diffServClfrStatus -- same as RFC3289 SYNTAX RowStatus { active(1) } WRITE-SYNTAX RowStatus { createAndGo(4), destroy(6) } DESCRIPTION "Support for createAndWait and notInService is not required."
OBJECT diffServClfrElementStatus -- same as RFC3289 SYNTAX RowStatus { active(1) } WRITE-SYNTAX RowStatus { createAndGo(4), destroy(6) } DESCRIPTION "Support for createAndWait and notInService is not required."
OBJECT diffServMultiFieldClfrAddrType SYNTAX InetAddressType { ipv4(1) } DESCRIPTION "An implementation is only required to support IPv4 addresses."
OBJECT diffServMultiFieldClfrSrcAddr SYNTAX InetAddress (SIZE(4)) DESCRIPTION "An implementation is only required to support IPv4 addresses."
OBJECT diffServMultiFieldClfrDstAddr SYNTAX InetAddress (SIZE(4)) DESCRIPTION "An implementation is only required to support IPv4 addresses."
OBJECT diffServAlgDropStatus -- same as RFC3289 SYNTAX RowStatus { active(1) } WRITE-SYNTAX RowStatus { createAndGo(4), destroy(6) } DESCRIPTION "Support for createAndWait and notInService is not required."
OBJECT diffServDataPathStorage SYNTAX StorageType { nonVolatile(3) } DESCRIPTION "An implementation is only required to support nonvolatile storage."
OBJECT diffServClfrStorage SYNTAX StorageType { nonVolatile(3) } DESCRIPTION "An implementation is only required to support nonvolatile storage."
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OBJECT diffServClfrElementStorage SYNTAX StorageType { nonVolatile(3) } DESCRIPTION "An implementation is only required to support nonvolatile storage."
OBJECT diffServMultiFieldClfrStorage SYNTAX StorageType { nonVolatile(3) } DESCRIPTION "An implementation is only required to support nonvolatile storage."
OBJECT diffServActionStorage SYNTAX StorageType { nonVolatile(3) } DESCRIPTION "An implementation is only required to support nonvolatile storage."
OBJECT diffServCountActStorage SYNTAX StorageType { nonVolatile(3) } DESCRIPTION "An implementation is only required to support nonvolatile storage."
OBJECT diffServAlgDropStorage SYNTAX StorageType { nonVolatile(3) } DESCRIPTION "An implementation is only required to support nonvolatile storage."
OBJECT diffServAlgDropType SYNTAX INTEGER { alwaysDrop(5) } DESCRIPTION "For DOCSIS subscriber management, this object is only used to provide packet filtering. Implementations need not support other values of this enumeration."
MODULE -- This module i.e., DOCS-IETF-SUBMGT-MIB
MANDATORY-GROUPS { docsSubMgtGroup }
OBJECT docsSubMgtCpeControlMaxCpeIp SYNTAX Integer32(0..16) DESCRIPTION "An implementation is only required to support up to sixteen addresses per modem."
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OBJECT docsSubMgtCpeMaxIpDefault SYNTAX Integer32(0..16) DESCRIPTION "An implementation is only required to support up to sixteen addresses per modem."
OBJECT docsSubMgtCpeIpAddressType SYNTAX InetAddressType { ipv4(1) } DESCRIPTION "An implementation is only required to support IPv4 addresses."
OBJECT docsSubMgtCpeIpAddr SYNTAX InetAddress (SIZE(4)) DESCRIPTION "An implementation is only required to support IPv4 addresses."
OBJECT docsSubMgtCmFilterSubDownstream SYNTAX Integer32(0..30) DESCRIPTION "An implementation is only required to support thirty filter groups."
OBJECT docsSubMgtCmFilterSubUpstream SYNTAX Integer32(0..30) DESCRIPTION "An implementation is only required to support thirty filter groups."
OBJECT docsSubMgtCmFilterCmDownstream SYNTAX Integer32(0..30) DESCRIPTION "An implementation is only required to support thirty filter groups."
OBJECT docsSubMgtCmFilterCmUpstream SYNTAX Integer32(0..30) DESCRIPTION "An implementation is only required to support thirty filter groups."
RFC 4036 DOCSIS Subscriber Management MIB April 2005
docsSubMgtCpeControlLearnable, docsSubMgtCpeControlReset, docsSubMgtCpeControlLastReset, docsSubMgtCpeMaxIpDefault, docsSubMgtCpeActiveDefault, docsSubMgtCpeLearnableDefault, docsSubMgtCpeIpAddressType, docsSubMgtCpeIpAddr, docsSubMgtCpeIpLearned, docsSubMgtCmFilterSubDownstream, docsSubMgtCmFilterSubUpstream, docsSubMgtCmFilterCmDownstream, docsSubMgtCmFilterCmUpstream, docsSubMgtFilterGroupIndex } STATUS current DESCRIPTION "The objects used to manage host-based cable modems via a set of CMTS enforced controls." ::= { docsSubMgtGroups 1 }
This document is based on work by Michael St. Johns, then at Excite@Home. Thanks to Guenter Roeck and Julie McGray for reviewing earlier versions. Thanks to Bert Wijnen, Mike Heard, and Harrie Hazewinkel for extensive later review. Thanks to the working group chairs, Richard Woundy and Jean-Francois Mule, for their extensive support.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
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[RFC2578] McCloghrie, K., Perkins, D., and J. Schoenwaelder, "Structure of Management Information Version 2 (SMIv2)", STD 58, RFC 2578, April 1999.
[RFC2579] McCloghrie, K., Perkins, D., and J. Schoenwaelder, "Textual Conventions for SMIv2", STD 58, RFC 2579, April 1999.
[RFC2580] McCloghrie, K., Perkins, D., and J. Schoenwaelder, "Conformance Statements for SMIv2", STD 58, RFC 2580, April 1999.
[ITU-T-J122] Second-Generation Transmission Systems for Interactive Cable Television Services, J.122, ITU-T, December, 2002.
[RFC2670] St. Johns, M., "Radio Frequency (RF) Interface Management Information Base for MCNS/DOCSIS compliant RF interfaces", RFC 2670, August 1999.
[RFC3289] Baker, F., Chan, K., and A. Smith, "Management Information Base for the Differentiated Services Architecture", RFC 3289, May 2002.
[RFC4001] Daniele, M., Haberman, B., Routhier, S., and J. Schoenwaelder, "Textual Conventions for Internet Network Addresses", RFC 4001, February 2005.
[RFC1858] Ziemba, G., Reed, D., and P. Traina, "Security Considerations for IP Fragment Filtering", RFC 1858, October 1995.
[RFC2669] St. Johns, M., "DOCSIS Cable Device MIB Cable Device Management Information Base for DOCSIS compliant Cable Modems and Cable Modem Termination Systems", RFC 2669, August 1999.
[RFC3128] Miller, I., "Protection Against a Variant of the Tiny Fragment Attack (RFC 1858)", RFC 3128, June 2001.
[RFC3410] Case, J., Mundy, R., Partain, D., and B. Stewart, "Introduction and Applicability Statements for Internet-Standard Management Framework", RFC 3410, December 2002.
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This MIB is intended to limit certain kinds of network behavior by subscriber hosts attached to cable modems, including, for example, IP spoofing. These limitations may be compromised, however, if the cable modem's identity or registration process is spoofed. The DOCSIS RFI and privacy specifications [ITU-T-J122] and [DOCSBPI] define a number of mechanisms for assuring modem identity.
For network filtering of TCP traffic to be effective, implementors MUST follow the recommendations in section 3.4.
There are a number of management objects defined in this MIB that have a MAX-ACCESS clause of read-write and/or read-create. These objects may be considered sensitive or vulnerable in some network environments. The support for SET operations in a non-secure environment without proper protection can have a negative effect on network operations.
Unauthorized SETs to this MIB can permit two major security problems with public cable network operation: IP address spoofing, and defeat of operator-defined packet filtering.
The following objects, if SET maliciously, would evade controls on address spoofing:
RFC 4036 DOCSIS Subscriber Management MIB April 2005
Some of the readable objects in this MIB module (i.e., objects with a MAX-ACCESS other than not-accessible) may be considered sensitive or vulnerable in some network environments. It is thus important to control even GET access to these objects and possibly even to encrypt the values of these objects when they are sent over the network via SNMP. The most sensitive is docsSubMgtCpeIpAddr within docsSubMgtCpeIpTable. Although docsSubMgtCpeIpTable is intended to control address spoofing, it includes information about the current subscriber address pool. This information may in itself be valuable to would-be spoofers.
SNMP versions prior to SNMPv3 did not include adequate security. Even if the network itself is secure (for example by using IPSec), there is no control as to who on the secure network is allowed to access and GET/SET (read/change/create/delete) the objects in this MIB module.
It is RECOMMENDED that implementers consider the security features as provided by the SNMPv3 framework (see [RFC3410], section 8), including full support for the SNMPv3 cryptographic mechanisms (for authentication and privacy).
Further, deployment of SNMP versions prior to SNMPv3 is NOT RECOMMENDED. Instead, it is RECOMMENDED to deploy SNMPv3 and to enable cryptographic security. It is then a customer/operator responsibility to ensure that the SNMP entity giving access to an instance of this MIB module is properly configured to give access to the objects only to those principals (users) who have legitimate rights to GET or SET (change/create/delete) them.
Author's Address
Wilson Sawyer 50 Kelly Brook Lane East Hampstead NH 03826
Phone: +1 603 382 7080 EMail: wsawyer@ieee.org
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