Internet A. Atlas
Internet-Draft JR. Rivers
Expires: June 12, 2006 Google, Inc.
R. Bonica
Juniper Networks
December 9, 2005
ICMP Extensions for Unnumbered Interfaces
draft-atlas-icmp-unnumbered-00
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Copyright (C) The Internet Society (2005).
Abstract
This memo defines extensions to ICMP that permit identification of
unnumbered interfaces. The interface the IP packet was received upon
can be identified by appending an ifIndex and/or a string describing
the interface. These extensions are defined to facilitate
troubleshooting in network with unnumbered interfaces and parallel
links.
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Table of Contents
1. Conventions Used In This Document . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Application to TRACEROUTE . . . . . . . . . . . . . . . . . . . 4
4. Interface Object . . . . . . . . . . . . . . . . . . . . . . . 4
5. Interface Description Object . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
8. Normative References . . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7
Intellectual Property and Copyright Statements . . . . . . . . . . 8
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1. Conventions Used In This Document
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 RFC2119 [4].
2. Introduction
IP routers use the Internet Control Message Protocol (ICMP) [1] to
convey control information to source hosts. Network operators use
this information to diagnose routing problems.
When a router generates an ICMP message, the source IP address can be
any address of the router. In common implementations, the IP address
selected is that of the incoming interface of the packet that
triggered the ICMP message. This allows easy identification of
specific interface and is very useful for troubleshooting
connectivity issues.
When a network uses unnumbered interfaces and parallel links, it is
not currently possible to identify the specific incoming interface of
a packet based upon the responding ICMP message. This memo defines
two extensions to ICMP that permit an operator to identify the
specific incoming interface traversed by a packet that triggered an
ICMP message.
These two extensions are motivated by the desire for similar
information to that for numbered interfaces. In the case of
traceroute, the ICMP message contains the interfaces's IP address;
then that IP address is commonly resolved via DNS to provide a
meaningful name for the interface that is easier for humans. One
extension permits a router to include the interface's ifIndex; this
can be used in combination with the source IP address for management
tasks. The second extension permits a router to include an interface
description string.
The inclusion of an interface description may also be useful for
numbered interfaces that use a private IP address that DNS cannot
resolve for supported users of traceroute and other ICMP message
triggers.
The ICMP message MUST include the IP header and leading payload
octets of the original datagram. As described in [2], an ICMP
Extension Structure Header MUST follow the octets from the original
datagram and come before any ICMP Extension Objects.
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3. Application to TRACEROUTE
ICMP extensions defined in this memo support enhancements to
TRACEROUTE. The enhanced TRACEROUTE application, like older
implementations, indicates which nodes the original datagram visited
en route to its destination. It differs from older implementations
in that it also reflects the incoming interface on which the original
packet arrived, even when that interface is unnumbered.
4. Interface Object
This section defines an ICMP extention object that can be appended to
the ICMP Time Exceeded and Destination Unreachable messages. One or
more Interface Objects can be appended to these messages.
Figure 1 depicts the Interface Object. It must be preceded by an
ICMP Extension Structure Header and an ICMP Object Header. Both are
defined in [2]. The ifIndex included is that assigned to the
interface by the router in as specified by the Interfaces Group MIB
[3].
Interface Class-Num = 2,
C-Type = 1 (Incoming Interface)
0 1 2 3
+-------------+-------------+-------------+-------------+
| Interface ifIndex |
+-------------+-------------+-------------+-------------+
Figure 1: Interface Object
5. Interface Description Object
This section defines an ICMP extention object that can be appended to
the ICMP Time Exceeded and Destination Unreachable messages. One or
more Interface Description Objects can be appended to these messages.
Figure 2 depicts the Interface Description Object. It must be
preceded by an ICMP Extension Structure Header and an ICMP Object
Header. Both are defined in [2].
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Interface Class-Num = 3,
C-Type = 1 (Incoming Interface Description encoded in ASCII)
0 1 2 3
+-------------+-------------+-------------+-------------+
| Interface Description |
+-------------+-------------+-------------+-------------+
Figure 2: Interface Description Object
Interface Description: This field MUST have a length that is a
multiple of 4 bytes; the string should be padded with zeroes as
necessary. The description can be either the same content as the
MIB-II ifDescription field or some other human-meaningful description
of the interface.
6. Security Considerations
These extensions can provide the user of traceroute with additional
network information that is not currently available. It may be
desirable to provide this information to a particular network's
operators and not to others. If such policy controls are desirable,
then an implementation could determine what extensions to include
based upon the destination IP address of the ICMP message. For
instance, there could be an interface description that is appropriate
for all potential recipients; a more detailed description and the
ifIndex could be included as well if the destination IP address is a
management address of the network that has administrative control of
the router.
7. IANA Considerations
IANA should should reserve from the ICMP Extension Object registry: 2
for the Interface Object and 3 for the Interface Description Object.
IANA should reserve from the Interface Object's C-type the value 1
for Incoming Interface. IANA should reserve from the Interface
Description Object's C-type the value 1 for Incoming Interface
Description in ASCII.
8. Normative References
[1] Postel, J., "Internet Control Message Protocol", STD 5, RFC 792,
September 1981.
[2] Bonica, R., "Extending the Internet Control Message Protocol
(ICMP)", draft-bonica-internet-icmp-00 (work in progress),
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September 2005.
[3] McCloghrie, K. and F. Kastenholz, "The Interfaces Group MIB
using SMIv2", RFC 2233, November 1997.
[4] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
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Authors' Addresses
Alia K. Atlas
Google, Inc.
1600 Amphitheatre Parkway
Mountain View, CA 94043
USA
Email: akatlas@google.com
J.R. Rivers
Google, Inc.
1600 Amphitheatre Parkway
Mountain View, CA 94043
USA
Email: jrrivers@google.com
Ronald P. Bonica
Juniper Networks
2251 Corporate Park Drive
Herndon, VA 20171
US
Email: rbonica@juniper.net
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