2.3.5 IP over Cable Data Network (ipcdn)

NOTE: This charter is a snapshot of the 50th IETF Meeting in Minneapolis, Minnesota. It may now be out-of-date. Last Modified: 14-Mar-01


Richard Woundy <rwoundy@cisco.com>
Andrew Valentine <a.valentine@eu.hns.com>

Internet Area Director(s):

Thomas Narten <narten@raleigh.ibm.com>
Erik Nordmark <nordmark@eng.sun.com>

Internet Area Advisor:

Thomas Narten <narten@raleigh.ibm.com>

Mailing Lists:

General Discussion:ipcdn@ietf.org
To Subscribe: http://www.ietf.org/mailman/listinfo/ipcdn
Archive: ftp://ftp.ietf.org/ietf-mail-archive/ipcdn

Description of Working Group:

The IETF IPCDN Working Group develops and standardizes SNMP MIBs for IP-capable data-over-cable systems, for example cable modems and associated cable-data equipment in a Headend. These MIBs cover not only cable data interfaces, but also management of cable-data equipment and systems.

The WG is also a forum for discussion of Internet-related issues in data-over-cable equipment and systems. In the event of a particular new Internet technology issue arising in the cable-data context, the WG will identify whether that is best handled within the IETF or is best handled by another standards body. In the event that new IETF work is identified, such items MAY be added that to the WG's charter, subject to normal IETF processes. Standardisation of MIBs for the EuroModem cable modem is within the scope of the IPCDN Working Group. Harmonisation of EuroModem MIBs and DOCSIS MIBs is desirable and will be examined by the IPCDN WG.
The IPCDN WG will also keep informed on what other groups in the industry are doing as it relates to the work of this working group.
Related groups:
The IEEE 802.14 WG was chartered to specify the physical layer and data link layer protocols for the CATV Data Network. The IEEE has discontinued the IEEE 802.14 effort, so that group no longer exists.
DOCSIS has completed its 1.0 versions of Data over Cable standards and is in the process of refining these standards to add additional functionality and to repair any flaws discovered in operational use. The IPCDN WG will update the documents produced which track the 1.0 versions accordingly. These include the RF Interface MIB and the Cable Device MIB. In addition, the operational and management issues of multicast over a Cable Data Network will be addressed.
Work items:
The IPCDN WG will address issues related to network management, especially as they concern HFC access networks. It is expected that other services (i.e. RSVP, IPSEC, etc.) will operate mostly unmodified.
- a MIB for managing the Telephone Modem Return Path (Telco Return) for 1-way cable modems. (draft-ietf-ipcdn-tri-mib-01.txt)
- a MIB for managing the Baseline Privacy system for DOCSIS. (draft-ietf-ipcdn-bpi-mib-01.txt), (draft-ietf-ipcdn-bpiplus-mib-00.txt)
- a MIB for managing the Quality of Service parameters for a Cable Data Network. (draft-ietf-ipcdn-qos-mib-02.txt)
- a MIB for managing Multicast (IGMP) over a Cable Data Network. (draft-ietf-ipcdn-igmp-mib-00.txt)
- a MIB for CMTS based customer management (draft-ietf-ipcdn-subscriber-mib-00.txt)
- Revisions to the Proposed Standard RF and CM MIBs to address SNMPv3 and IPv6 compliance and interoperability issues.

Goals and Milestones:

Feb 00


Post final I-D on Baseline Privacy MIB; Last call

Feb 00


Post I-Ds revising RF and CM MIBs to support DOCSIS1.1 and for compliance with SNMPv3 and IPv6

Feb 00


Submit Baseline Privacy MIB to IESG for publication as a Standards Track RFC

Feb 00


Submit updated RF and CM MIBs to IESG with implementation statement for advancement to Draft Standard

Jun 00


Revaluate charter and milestones.

Request For Comments:






Cable Device Management Information Base for DOCSIS compliant Cable Modems and Cable Modem Termination Systems



Radio Frequency (RF) Interface Management Information Base for MCNS/DOCSIS compliant RF interfaces

Current Meeting Report

Minneapolis, MN
March 19, 2001

Reported by Pak Siripunkaw (psiripunkaw@broadband.att.com)

WG Meeting Summary

Approximately 35 members of the IP over Cable Data Networks WG met at the Minneapolis IETF on March 19, 2001. The WG discussed the status of most of its work items as well as the ongoing charter revision. The WG also discussed the common problems with respect to TCP port filtering and matching that exist in many of the WG documents. Since the last IETF meeting, the WG submitted two new internet-drafts (not including two drafts that missed the submission deadline but were posted to the mailing list), and six updates to existing internet-drafts.

WG Status and Charter Revision (Richard Woundy)

Richard Woundy discussed the overall status of work items in the working group. The BPI MIB has been published as RFC 3083, the Euromodem/DVB NIU MIB is in WG last-call, and the DOCSIS QoS MIB and Application of the IGMP MIB (RFC 2933) to DOCSIS Devices are about to start WG last-call.

It is unclear whether the Application of the IGMP MIB is implemented in a DOCSIS device yet. The MIB is required to be implemented for DOCSIS 1.1 certification, though.

A presentation for the DOCSIS QoS MIB was not available for the meeting, but the WG consensus appeared to be in favor of bringing this document to WG last-call.

There has been little progress on the proposed Account Management Control MIB since the last WG meeting. The WG may want to re-evaluate this project as a work item, possibly dropping it.

The next IPCDN meeting is sometime during the week of August 5-10 in London, and a number of work items need to be completed by that time.

The co-chairs have been formulating and proposing significant changes to the WG charter, to update the description (add text about DOCSIS 1.1 and Euromodem), modify work items, and revamp the overall schedule. The charter is currently under evaluation by our Area Directors.

EuroModem NIU Device and Interface MIBs (slides by Andrew Valentine)

Richard Woundy presented slides from Andrew Valentine, which discuss the Euromodem NIU Device MIB version -03 -- currently in WG last-call. Richard Woundy has submitted editorial comments to the author. Andrew plans to collect all comments from the last-call period, issue draft -04, republish with a one week review time, and submit to the IESG as a standards track specification. The WG raised no technical objections with the draft at this meeting.

Andrew also has submitted the first version of the Euromodem NIU Interface MIB, which organizes DVB-specific interface management objects into MAC layer, RF downstream, and RF upstream groups. There are some analogies between this MIB and RFC 2670, particularly in the handling of the interface layering model.

EuroModem INA Device and Interface MIBs (slides by Jens Pedersen)

Richard Woundy presented slides from Jens Pedersen, which discuss the first versions of the Euromodem INA Interface MIB and the Euromodem INA Device MIB. The INA Interface MIB defines DVB-specific interface management objects for MAC layer, RF downstream, RF upstream, and NIU provisioning and management. The INA Device MIB defines optional object groups for management of general device control, network management access, software images, DHCP relay configuration, event handling and logging, Ethernet and IP filters, and NIU IP address and subnet controls.

DOCSIS Application of RFC 2933 MIB (slides by Howard Abramson)

Richard Woundy presented slides from Howard Abramson, which discuss changes in version -02 of the DOCSIS Application of the IGMP MIB. In this version, the author clarifies "interface robustness" for the CM HFC interface (i.e. it controls the number of retransmissions of Unsolicited Membership Reports in the absence of a response), emphasizes that igmpCacheIfIndex is a table index, and clarifies the behavior of the "IGMP cache" when a row is deleted (i.e. the row may be recreated upon receipt of a new IGMP Membership Report). The WG raised no technical objections with the draft at this meeting.

Subscriber Management MIB (slides by Wilson Sawyer)

Richard Woundy presented slides from Wilson Sawyer, which discuss changes in version -03 of the Subscriber Management MIB, as well as justification for its current form. The major change in version -03 is alignment of the MIB with RFC 2851 for Internet address-related objects; the specification also takes care not to mandate IPv6 capability for MIB compliance.

In the last WG meeting, some folks voiced their concerns about the implementation complexity of this MIB. Wilson provides three justifications for the current MIB content: (1) multiple vendors are implementing this MIB (which suggests the MIB is implementable), (2) CableLabs requires implementation of this MIB for DOCSIS 1.1 certification, and (3) the filtering functionality and source address verification are needed for the protection of the cable network.

The WG expressed confusion about the OID for the base of the Subscriber Management MIB subtree. While "{ experimental 83 4 }" is the current OID, the current text suggests that the OID would be modified to "{ docsDev 4 }". Unfortunately, Mike StJohns already assigned this OID to docsDevConformanceV2 in the RFC 2669 update. The WG co-chairs will assign a new OID for the Subscriber Management MIB -- in all likelihood, "{ docsDev 5 }".

Some WG members have sent technical issues to the author and/or the mailing list, which should be resolved. One technical issue, concerning TCP traffic filtering and IP fragmentation, was discussed separately since it broadly applies to a number of WG specifications (see below).

DOCSIS Notifications (slides by Junming Gao)

Richard Woundy presented slides from Junming Gao, which discuss changes in version -01 of the DOCSIS Notification MIB. In this version, the author adheres to RFC 2576 by adding "0" to key OID prefixes, adds trap control objects, adds a reference to the event throttling control of RFC 2669, and modifies some object names for clarity.

The WG discussed whether the event throttling mechanism of RFC 2669 applied to events not defined in this internet draft. The WG agreed that the mechanism also applies to generic SNMP traps such as linkUp and linkDown.

RFC 2669 and 2670 Updates (Richard Woundy)

Richard Woundy presented slides which discuss the latest updates to the DOCSIS Cable Device MIB and the DOCSIS RFI MIB (RFCs 2669 and 2670). In version -01 of the update to RFC 2669, the author aligns the MIB with RFC 2851 for most Internet address-related objects, adds an object to support the DOCSIS Application of RFC 2933 MIB, and adds references to the Event Notification and Subscriber Management MIBs. Future work includes aligning this MIB with the DOCSIS QoS MIB and the DOCSIS OSSI specification, choosing one mechanism to support multiple CPE-side interfaces on a CM (DOCSIS OSSI approach versus InterfaceSet objects), clarifying the handling of generic traps, and fixing issues with the docsDevNmAccessTable.

In the first version of the update to RFC 2670, the author aligns Internet address-related object with RFC 2851, modifies objects and compliances for EuroDOCSIS and European cable plant characteristics, clarifies object descriptions for objects with the BITS syntax, and fixes other object definition errors. Future work includes aligning this MIB with the DOCSIS Notification MIB (i.e. adding objects from IF-EXT-MIB), clarifying the upstream channel transmit timing offset, and aligning with the most recent version of the Interfaces Group MIB, RFC 2863.

The WG felt that generic traps (e.g. linkUp and linkDown) should be included in the RFC 2669 throttling control.

A WG member suggested that the WG determine the extent of the overlap between the RFC 2669 event log and RFC 3014, "Notification Log MIB".

A WG member suggested that RFC 2669 may need more objects for maximum CPE limits. One object might indicate how many CPE devices the CM can support in firmware; another object might indicate the maximum number of CPE devices that should be allowed to communicate across the cable network by operator configuration.

A WG member pointed out that the docsDevEvReporting object uses the BITS syntax, which needs to be clarified (i.e. bit-ordering) in the description.

A WG member pointed out that slide 8 made reference to RFC 2683, a typo for RFC 2863. This is corrected in the powerpoint slides submitted to the IETF.

A WG member notes that the Interfaces Group MIB, RFC 2863, now has a companion specification, The Inverted Stack Table Extension to the Interfaces Group MIB, RFC 2864. The author agreed to investigate the impact on RFC 2670.

Pak Siripunkaw agreed to help Rich reconcile the RFC 2670 update with the DOCSIS OSSI.

TCP Port Filtering Issues (Richard Woundy)

Richard Woundy presented slides on potential issues with TCP port filtering and matching in various WG work items. RFC 1858 describes problems related to IP fragmentation and TCP port filtering, and some implementation workarounds. Richard recommends that cable device implementations performing TCP/UDP port filtering should ignore non-initial IP fragments, but should drop all TCP fragments with offset 1, to prevent tiny-gram and port-overwrite attacks. Richard also recommends that cable device implementations performing TCP port matching (e.g. DOCSIS QoS MIB) should not match non-initial IP fragments, and applications requiring special handling should use Path MTU Discovery (RFC 1191).

The WG agreed that this is a problem that needs to be fixed immediately.

After the WG session, a WG member pointed out that RFC 1858 offers another workaround for TCP port filtering: a forwarding device can reassemble the IP fragments before applying the port filters and forwarding the datagram. His suggestion was to allow this implementation workaround as an alternative.


EuroModem MIB
Internet drafts DVB INA MIBs
Docsis 1.1 IGMP MIB Application Note
Subscriber Management MIB
Event Notification Management Information Base for DOCSIS 1.1
Issues with TCP Port Filtering and Matching
RFC 2669 and 2670 Updates