Network Working Group M. St. Johns, Ed.
Request for Comments: 2669 @Home Network
Category: Proposed Standard August 1999
DOCSIS Cable Device MIB
Cable Device Management Information Base
for DOCSIS compliant Cable Modems and
Cable Modem Termination Systems
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 (1999). All Rights Reserved.
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 basic set of managed objects for SNMP-
based management of DOCSIS 1.0 compliant Cable Modems and Cable Modem
Termination Systems.
This memo specifies a MIB module in a manner that is compliant to the
SNMP SMIv2 [5][6][7]. The set of objects is consistent with the SNMP
framework and existing SNMP standards.
This memo is a product of the IPCDN working group within the Internet
Engineering Task Force. Comments are solicited and should be
addressed to the working group's mailing list at ipcdn@terayon.com
and/or the author.
Table of Contents
1 The SNMP Management Framework ................................... 2
2 Glossary ........................................................ 3
2.1 CATV .......................................................... 3
2.2 CM ............................................................ 3
2.3 CMTS .......................................................... 4
2.4 DOCSIS ........................................................ 4
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RFC 2669 DOCSIS Cable Device MIB August 1999
2.5 Downstream .................................................... 4
2.6 Head-end ...................................................... 4
2.7 MAC Packet .................................................... 4
2.8 MCNS .......................................................... 4
2.9 RF ............................................................ 4
2.10 Upstream ..................................................... 4
3 Overview ........................................................ 4
3.1 Structure of the MIB .......................................... 5
3.2 Management requirements ....................................... 6
3.2.1 Handling of Software upgrades ............................... 6
3.2.2 Events and Traps ............................................ 6
3.2.3 Trap Throttling ............................................. 8
3.2.3.1 Trap rate throttling ...................................... 8
3.2.3.2 Limiting the trap rate .................................... 8
3.3 Protocol Filters .............................................. 9
3.3.1 Inbound LLC Filters - docsDevFilterLLCTable ................ 10
3.3.2 Special Filters ............................................ 10
3.3.2.1 IP Spoofing Filters - docsDevCpeTable .................... 10
3.3.2.2 SNMP Access Filters - docsDevNmAccessTable ............... 10
3.3.3 IP Filtering - docsDevIpFilterTable ........................ 11
3.3.4 Outbound LLC Filters ....................................... 13
4 Definitions .................................................... 13
5 Acknowledgments ................................................ 51
6 References ..................................................... 51
7 Security Considerations ........................................ 52
8 Intellectual Property .......................................... 54
9 Author's Address ............................................... 54
10 Full Copyright Statement ...................................... 55
1. The SNMP Management Framework
The SNMP Management Framework presently consists of five major
components:
o An overall architecture, described in RFC 2571 [1].
o Mechanisms for describing and naming objects and events for the
purpose of management. The first version of this Structure of
Management Information (SMI) is called SMIv1 and described in STD
16, RFC 1155 [2], STD 16, RFC 1212 [3] and RFC 1215 [4]. The
second version, called SMIv2, is described in STD 58, RFC 2578
[5], STD 58, RFC 2579 [6] and STD 58, RFC 2580 [7].
o Message protocols for transferring management information. The
first version of the SNMP message protocol is called SNMPv1 and
described in STD 15, RFC 1157 [8]. A second version of the SNMP
message protocol, which is not an Internet standards track
protocol, is called SNMPv2c and described in RFC 1901 [9] and RFC
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1906 [10]. The third version of the message protocol is called
SNMPv3 and described in RFC 1906 [10], RFC 2572 [11] and RFC 2574
[12].
o Protocol operations for accessing management information. The
first set of protocol operations and associated PDU formats is
described in STD 15, RFC 1157 [8]. A second set of protocol
operations and associated PDU formats is described in RFC 1905
[13].
o A set of fundamental applications described in RFC 2573 [14] and
the view-based access control mechanism described in RFC 2575
[15].
Managed objects are accessed via a virtual information store, termed
the Management Information Base or MIB. Objects in the MIB are
defined using the mechanisms defined in the SMI.
This memo specifies a MIB module that is compliant to the SMIv2. A
MIB conforming to the SMIv1 can be produced through the appropriate
translations. The resulting translated MIB must be semantically
equivalent, except where objects or events are omitted because no
translation is possible (use of Counter64). Some machine readable
information in SMIv2 will be converted into textual descriptions in
SMIv1 during the translation process. However, this loss of machine
readable information is not considered to change the semantics of the
MIB.
2. Glossary
The terms in this document are derived either from normal cable
system usage, or from the documents associated with the Data Over
Cable Service Interface Specification process.
2.1. CATV
Originally "Community Antenna Television", now used to refer to any
cable or hybrid fiber and cable system used to deliver video signals
to a community.
2.2. CM Cable Modem.
A CM acts as a "slave" station in a DOCSIS compliant cable data
system.
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2.3. CMTS Cable Modem Termination System.
A generic term covering a cable bridge or cable router in a head-end.
A CMTS acts as the master station in a DOCSIS compliant cable data
system. It is the only station that transmits downstream, and it
controls the scheduling of upstream transmissions by its associated
CMs.
2.4. DOCSIS
"Data Over Cable Interface Specification". A term referring to the
ITU-T J.112 Annex B standard for cable modem systems [20].
2.5. Downstream
The direction from the head-end towards the subscriber.
2.6. Head-end
The origination point in most cable systems of the subscriber video
signals. Generally also the location of the CMTS equipment.
2.7. MAC Packet
A DOCSIS PDU.
2.8. MCNS
"Multimedia Cable Network System". Generally replaced in usage by
DOCSIS.
2.9. RF
Radio Frequency.
2.10. Upstream
The direction from the subscriber towards the head-end.
3. Overview
This MIB provides a set of objects required for the management of
DOCSIS compliant Cable Modems (CM) and Cable Modem Termination
Systems (CMTS). The specification is derived from the DOCSIS Radio
Frequency Interface specification [16]. Please note that the DOCSIS
1.0 standard only requires Cable Modems to implement SNMPv1 and to
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RFC 2669 DOCSIS Cable Device MIB August 1999
process IPv4 customer traffic. Design choices in this MIB reflect
those requirements. Future versions of the DOCSIS standard are
expected to require support for SNMPv3 and IPv6 as well.
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 [19].
3.1. Structure of the MIB
This MIB is structured into seven groups:
o The docsDevBase group extends the MIB-II 'system' group with
objects needed for cable device system management.
o The docsDevNmAccessGroup provides a minimum level of SNMP
access security (see Section 3 of [18]).
o The docsDevSoftware group provides information for network-
downloadable software upgrades. See "Handling of Software
Upgrades" below..
o The docsDevServer group provides information about the
progress of the interaction between the CM or CMTS and
various provisioning servers.
o The docsDevEvent group provides control and logging for event
reporting.
o The docsDevFilter group configures filters at link layer and
IP layer for bridged data traffic. This group consists of a
link-layer filter table, docsDevFilterLLCTable, which is used
to manage the processing and forwarding of non-IP traffic; an
IP packet classifier table, docsDevFilterIpTable, which is
used to map classes of packets to specific policy actions; a
policy table, docsDevFilterPolicyTable, which maps zero or
more policy actions onto a specific packet classification,
and one or more policy action tables.
At this time, this MIB specifies only one policy action
table, docsDevFilterTosTable, which allows the manipulation
of the type of services bits in an IP packet based on
matching some criteria. The working group may add additional
policy types and action tables in the future, for example to
allow QOS to modem service identifier assignment based on
destination.
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o The docsDevCpe group provides control over which IP addresses
may be used by customer premises equipment (e.g. PCs)
serviced by a given cable modem. This provides anti-spoofing
control at the point of origin for a large cable modem
system. This group is separate from docsDevFilter primarily
as this group is only implemented on the Cable Modem (CM) and
MUST NOT be implemented on the Cable Modem Termination System
(CMTS).
3.2. Management requirements
3.2.1. Handling of Software upgrades
The Cable Modem software upgrade process is documented in [16]. From
a network management station, the operator:
o sets docsDevSwServer to the address of the TFTP server for
software upgrades
o sets docsDevSwFilename to the file pathname of the software
upgrade image
o sets docsDevSwAdminStatus to upgrade-from-mgt
One reason for the SNMP-initiated upgrade is to allow loading of a
temporary software image (e.g., special diagnostic software) that
differs from the software normally used on that device without
changing the provisioning database.
Note that software upgrades should not be accepted blindly by the
cable device. The cable device may refuse an upgrade if:
o The download is incomplete.
o The file contents are incomplete or damaged.
o The software is not intended for that hardware device (may
include the case of a feature set that has not been purchased
for this device).
3.2.2. Events and Traps
This MIB provides control facilities for reporting events through
syslog, traps, and non-volatile logging. If events are reported
through traps, the specified conventions must be followed. Other
means of event reporting are outside the scope of this document.
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The definition and coding of events is vendor-specific. In deference
to the network operator who must troubleshoot multi-vendor networks,
the circumstances and meaning of each event should be reported as
human-readable text. Vendors SHOULD provide time-of-day clocks in
CMs to provide useful timestamping of events.
For each vendor-specific event that is reportable via TRAP, the
vendor must create an enterprise-specific trap definition. Trap
definitions MUST include the event reason encoded as DisplayString
and should be defined as:
trapName NOTIFICATION-TYPE
OBJECTS {
ifIndex,
eventReason,
other useful objects
}
STATUS current
DESCRIPTION
"trap description"
::= Object Id
Note that ifIndex is only included if the event or trap is interface
related.
An example (fake) vendor defined trap might be:
xyzVendorModemDropout NOTIFICATION-TYPE
OBJECTS {
eventReason,
xyzModemHighWatermarkCount
}
STATUS current
DESCRIPTION
"Sent by a CMTS when a configurable number of modems
(xyzModemHysteresis) de-register or become unreachable during
the sampling period (5 minutes). Used to warn a management
station about a catastrophic cable plant outage."
::= { xyzTraps 23 }
In this example eventReason is a DisplayString providing a human
readable error message, and xyzModemHighWatermarkCount is a Gauge32
which indicates the maximum number of modems during the epoch.
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RFC 2669 DOCSIS Cable Device MIB August 1999
The last digit of the trap OID for enterprise-specific traps must
match docsDevEvId. For SNMPv1-capable Network Management systems,
this is necessary to correlate the event type to the trap type. Many
Network Management systems are only capable of trap filtering on an
enterprise and single-last-digit basis.
3.2.3. Trap Throttling
The CM and CMTS MUST provide support for trap message throttling as
described below. The network operator can employ message rate
throttling or trap limiting by manipulating the appropriate MIB
variables.
3.2.3.1. Trap rate throttling
Network operators may employ either of two rate control methods. In
the first method, the device ceases to send traps when the rate
exceeds the specified maximum message rate. It resumes sending traps
only if reactivated by a network management station request.
In the second method, the device resumes sending traps when the rate
falls below the specified maximum message rate.
The network operator configures the specified maximum message rate by
setting the measurement interval (in seconds), and the maximum number
of traps to be transmitted within the measurement interval. The
operator can