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Internet A. Atlas
Internet-Draft Google, Inc.
Expires: August 5, 2006 JR. Rivers
Nuova Systems
R. Bonica
Juniper Networks
N. Shen
E. Chen
Cisco Systems
February 2006
ICMP Extensions for Unnumbered Interfaces
draft-atlas-icmp-unnumbered-01
Status of this Memo
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Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
This memo defines extensions to ICMP that permit identification of
unnumbered interfaces. The interface the triggering IPv4 packet was
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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.
Additionally, to facilitate debugging of numbered interfaces, the
IPv4 address of the interface the triggering IPv4 packet was received
upon can be identified by appending the IPv4 address.
Table of Contents
1. Conventions Used In This Document . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Application to TRACEROUTE . . . . . . . . . . . . . . . . . . . 4
4. Interface ID Object . . . . . . . . . . . . . . . . . . . . . . 4
5. Interface Description Object . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
9.1. Normative References . . . . . . . . . . . . . . . . . . . 6
9.2. Informative References . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8
Intellectual Property and Copyright Statements . . . . . . . . . . 9
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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 [RFC2119].
2. Introduction
IP routers use the Internet Control Message Protocol (ICMP) [RFC0792]
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, as
specified in RFC1812 [RFC1812], MUST be either one of the IP
addresses associated with the transmitting interface or, for
unnumbered interfaces, the router's router-id. When the transmitting
interface is the same as the incoming interface of the packet that
triggered the ICMP message and that interface is numbered, this
allows easy identification of specific interface and is very useful
for troubleshooting connectivity issues. The transmitting and
incoming interfaces may be different due to an asymmetric return
path, which can occur due to asymmetric link costs or ECMP. This
specification provides an extension so that the IPv4 address of the
incoming interface can be explicitly reported.
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 additional 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.
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The ICMP message MUST include the IP header and leading payload
octets of the original datagram. As described in [I-D.bonica-
internet-icmp], an ICMP Extension Structure Header MUST follow the
octets from the original datagram and come before any ICMP Extension
Objects.
3. Application to TRACEROUTE
ICMP extensions defined in this memo support enhancements to
TRACEROUTE (the reasons are discussed in [I-D.bonica-internet-icmp]).
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 triggering
packet arrived, even when that interface is unnumbered.
4. Interface ID Object
This section defines an ICMP extension object that can be appended to
the ICMP Time Exceeded and Destination Unreachable messages. An
Interface ID Object of c-type 1 can be appended to these messages.
The incoming interface is the one upon which the packet which
triggered the ICMP message was received. If the incoming interface
is unnumbered, then an Interface ID Object of c-type 1 SHOULD be
included in the ICMP Time Exceeded or Destination Unreachable
message. If the incoming interface has an IPv4 address, then an
Interface ID Object of c-type 1 MAY be included in the ICMP Time
Exceeded and Destination Unreachable messages; additionally, one or
Interface ID Objects of c-type 2 MAY be included in those messages.
Figure 1 depicts the Interface ID Object. It must be preceded by an
ICMP Extension Structure Header and an ICMP Object Header. Both are
defined in [I-D.bonica-internet-icmp]. The ifIndex included is that
assigned to the interface by the router in as specified by the
Interfaces Group MIB [RFC2863].
Class-Num = 2,
C-Type = 1 (Specifies ifIndex of incoming interface)
Length = 8
0 1 2 3
+-------------+-------------+-------------+-------------+
| Interface ifIndex |
+-------------+-------------+-------------+-------------+
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Figure 1: Interface ID Object - ifIndex
Class-Num = 2,
C-Type = 2
Specifies an IPv4 address of the incoming interface.
Length = 8
0 1 2 3
+-------------+-------------+-------------+-------------+
| an IPv4 address of the incoming interface |
+-------------+-------------+-------------+-------------+
Figure 2: Interface ID Object - IPv4 address
5. Interface Description Object
This section defines an ICMP extention object that can be appended to
the ICMP Time Exceeded and Destination Unreachable messages. An
Interface Description Object with c-type 1 or 2 can be appended to
these messages. If the incoming interface is unnumbered, then an
Interface ID Object of C-type 1 MAY be included in the ICMP Time
Exceeded message and Destination Unreachable messages.
Figure 3 depicts the Interface Description Object. It must be
preceded by an ICMP Extension Structure Header and an ICMP Object
Header. Both are defined in [I-D.bonica-internet-icmp].
Interface Class-Num = 3,
C-Type = 1 or 2
0 1 2 3
+-------------+-------------+-------------+-------------+
| Interface Description |
+-------------+-------------+-------------+-------------+
// Interface Description, continued //
+-------------+-------------+-------------+-------------+
| Interface Description, continued |
+-------------+-------------+-------------+-------------+
Figure 3: Interface Description Object
C-Type 1: This contains the description of the incoming interface.
Human-readable text for this c-type MUST be provided in the US-ASCII
charset [US-ASCII] using the Default Language [RFC2277].
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C-Type 2: This contains the description of the incoming interface.
Human-readable text for this c-type MUST be provided in the UTF-8
charset [RFC3629] using the Default Language [RFC2277].
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 SHOULD be the MIB-II ifName [RFC2863] but
MAY be 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, the ifIndex might be appropriate for all potential
recipients; the description 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 ID Object and 3 for the Interface Description
Object. IANA should reserve from the Interface ID Object's c-type
the value 1 for Incoming Interface ifIndex and the value 2 for the
Incoming Interface IPv4 address. IANA should reserve from the
Interface Description Object's c-type the value 1 for the incoming
interface description in ASCII and the value 2 for the incoming
interface description in UTF-8.
8. Acknowledgements
The authors would like to thank Carlos Pignataro and Sasha Vainshtein
for their comments and suggestions.
9. References
9.1. Normative References
[I-D.bonica-internet-icmp]
Bonica, R., "Extending the Internet Control Message
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Protocol (ICMP)", draft-bonica-internet-icmp-01 (work in
progress), January 2006.
[RFC0792] Postel, J., "Internet Control Message Protocol", STD 5,
RFC 792, September 1981.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2863] McCloghrie, K. and F. Kastenholz, "The Interfaces Group
MIB", RFC 2863, June 2000.
9.2. Informative References
[RFC1812] Baker, F., "Requirements for IP Version 4 Routers",
RFC 1812, June 1995.
[RFC2277] Alvestrand, H., "IETF Policy on Character Sets and
Languages", BCP 18, RFC 2277, January 1998.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[US-ASCII]
"Coded Character Set -- 7-bit American Standard Code for
Information Interchange, ANSI X3.4-1986".
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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
Nuova Systems
Email: jrrivers@nuovasystems.com
Ronald P. Bonica
Juniper Networks
2251 Corporate Park Drive
Herndon, VA 20171
USA
Email: rbonica@juniper.net
Naiming Shen
Cisco Systems
225 West Tasman Drive
San Jose, CA 95134
USA
Email: naiming@cisco.com
Enke Chen
Cisco Systems
170 West Tasman Drive
San Jose, CA 95134
USA
Email: enkechen@cisco.com
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