Internet A. Atlas, Ed.
Internet-Draft Google, Inc.
Expires: September 5, 2007 R. Bonica
Juniper Networks
JR. Rivers
Nuova Systems
N. Shen
E. Chen
Cisco Systems
March 4, 2007
ICMP Extensions for Unnumbered Interfaces
draft-atlas-icmp-unnumbered-02
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Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
This memo defines extensions to ICMP that permit identification of
unnumbered interfaces. The interface the triggering IPv4 or IPv6
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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. Additionally, to facilitate debugging of numbered
interfaces, an IPv4 or IPv6 address of the interface the triggering
IPv4 or IPv6 packet was received upon can be identified by appending
an IPv4 or IPv6 address.
Table of Contents
1. Conventions Used In This Document . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Application to TRACEROUTE . . . . . . . . . . . . . . . . . . 4
4. Interface Information Object . . . . . . . . . . . . . . . . . 4
4.1. C-type meaning in an Interface Information Object . . . . 5
4.2. Interface Description Sub-Object . . . . . . . . . . . . . 5
4.3. Interface Information Object Description . . . . . . . . . 6
4.4. Usage . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
8.1. Normative References . . . . . . . . . . . . . . . . . . . 11
8.2. Informative References . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
Intellectual Property and Copyright Statements . . . . . . . . . . 13
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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 an IPv4 or IPv6 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. The extension
defined in this memo permits an operator to identify the specific
incoming interface traversed by a packet that triggered an ICMP
message.
This extension is motivated by the desire for similar information to
that for numbered interfaces. In the case of traceroute, the ICMP
message contains one of 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 attribute permits a
router to include a short interface description string. Another
attribute of the extension permits a router to include the
interface's ifIndex; this can be used in combination with the source
IP address for management tasks. An interface's ifIndex may be used
(for example, see Section 12.4.1 of RFC2328 [RFC2328]) when the
interface is unnumbered and some identification unique to that router
is desired.
The inclusion of an interface description may also be useful for
numbered interfaces that use a private IP address that DNS cannot
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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
[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 Information Object
This section defines an ICMP extension object that can be appended to
the ICMPv4 Time Exceeded, ICMPv4 Destination Unreachable, ICMPv4
Parameter Problem, ICMPv6 Time Exceeded, and ICMPv6 Destination
Unreachable messages, as described in [I-D.bonica-internet-icmp].
For the description of the Interface Information Object, the incoming
interface is the one upon which the packet which triggered the ICMP
message was received. To minimize the use of extra bytes required
for this extension, there are four different pieces of information
that can appear in an Interface Information Object.
1. If the interface of interest has at least one IPv4 address and
the triggering packet was IPv4, then one of the interface's IPv4
addresses MAY be included.
2. If the interface of interest has at least one IPv6 address and
the triggering packet was IPv6, then one of the interface's IPv6
addresses MAY be included.
3. The ifIndex of the interface of interest MAY be included. This
is the ifIndex assigned to the interface by the router in as
specified by the Interfaces Group MIB [RFC2863].
4. An interface description string of no more than 31 bytes MAY be
included.
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4.1. C-type meaning in an Interface Information Object
For this object, the c-type is split into two fields, a 2-bit
interface-role field and a 6-bit included-information field. This is
illustrated below.
Bit 7 6 | 5 4 3 2 1 0
+-------+-------+-------+-------+-------+-------+-------+-------+
| Interface Role| Rsvd | Rsvd | index | IPv4 | IPv6 | descr |
+-------+-------+-------+-------+-------+-------+-------+-------+
Interface Role : This 2-bit field [6:7] indicates the role of the
interface being identified. The enumerated values
are given below.
0 : This object describes the incoming interface.
1 : This object describes the outgoing interface.
2-3 : Undefined by this memo and to be assigned by IANA
Included Information: This 6-bit field [0:5] indicates what
information is included in the object. The
information must be included in the same order
as the bits (from highest to lowest).
bit
5 : This bit is reserved for future use and MUST be set to 0.
4 : This bit is reserved for future use and MUST be set to 0.
3 : When set, this bit indicates that the ifIndex of the interface
is included. When clear, the ifIndex is not included.
2 : When set, this indicates that an IPv4 address of the interface
is included. When clear, no IPv4 address is included.
1 : When set, this indicates that an IPv6 address of the interface
is included. When clear, no IPv6 address is included.
0 : When set, this indicates that an Interface Description
Sub-object for the interface is included. When clear, it is
not included.
C-Type for the Interface Information Object
4.2. Interface Description Sub-Object
The Interface Description Sub-Object MUST have a length that is a
multiple of 4 bytes and MUST NOT exceed 32 bytes; the string should
be padded with zeroes as necessary. The description text SHOULD be
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the MIB-II ifName [RFC2863] but MAY be some other human-meaningful
description of the interface.
The Interface Description Sub-Object consists of two fields. The
first 1-byte field indicates the character set type used by the
second field. The second field contains the human-readable
description text.
byte 0 1 31
+--------------+----..............-------+
| charset type | description text |
+--------------+----..............-------+
Interface Description Sub-Object
charset type 0 : This indicates that the human-readable description
text MUST be provided in the US-ASCII charset [US-ASCII] using the
Default Language [RFC2277].
charset type 1 : This indicates that the human-readable description
text MUST be provided in the UTF-8 charset [RFC3629] using the
Default Language [RFC2277].
4.3. Interface Information Object Description
Figure 3 depicts the Interface Information Object, with some valid
permutations. It must be preceded by an ICMP Extension Structure
Header and an ICMP Object Header. Both are defined in
[I-D.bonica-internet-icmp].
Although all examples show an Interface Description Sub-object of
length 32, this is only for illustration and depicts the maximum
allowable length.
Class-Num = 2
Example 1: Interface with only description
C-Type = 00000001b // Indicates incoming interface
Length = 36 (4 + 32)
0 1 2 3
+--------------+--------------+--------------+--------------+
| Interface Description, word 1 |
+--------------+--------------+--------------+--------------+
... ...
+--------------+--------------+--------------+--------------+
| Interface Description , word 8 |
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+--------------+--------------+--------------+--------------+
Example 2: Interface with only ifIndex
C-Type = 00001000b // Indicates incoming interface
Length = 8 (4 + 4)
0 1 2 3
+--------------+--------------+--------------+--------------+
| Interface ifIndex |
+--------------+--------------+--------------+--------------+
Example 3: Unnumbered Interface with ifIndex and description
C-Type = 00001001b // Indicates incoming interface
Length = 40 (4 + 4 + 32)
0 1 2 3
+--------------+--------------+--------------+--------------+
| Interface ifIndex |
+--------------+--------------+--------------+--------------+
| Interface Description, word 1 |
+--------------+--------------+--------------+--------------+
... ...
+--------------+--------------+--------------+--------------+
| Interface Description , word 8 |
+--------------+--------------+--------------+--------------+
Example 4: IPv4 interface with ifIndex and description
C-Type = 00001101b // Indicates incoming interface
Length = 44 (4 + 4 + 4 + 32)
0 1 2 3
+--------------+--------------+--------------+--------------+
| Interface ifIndex |
+--------------+--------------+--------------+--------------+
| IPv4 address |
+--------------+--------------+--------------+--------------+
| Interface Description, word 1 |
+--------------+--------------+--------------+--------------+
... ...
+--------------+--------------+--------------+--------------+
| Interface Description , word 8 |
+--------------+--------------+--------------+--------------+
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Example 5: IPv4 interface with ifIndex
C-Type = 00001100b // Indicates incoming interface
Length = 12 (4 + 4 + 4)
0 1 2 3
+--------------+--------------+--------------+--------------+
| Interface ifIndex |
+--------------+--------------+--------------+--------------+
| IPv4 address |
+--------------+--------------+--------------+--------------+
Example 6: IPv4 interface with description
C-Type = 00000101b // Indicates incoming interface
Length = 40 (4 + 4 + 32)
0 1 2 3
+--------------+--------------+--------------+--------------+
| IPv4 address |
+--------------+--------------+--------------+--------------+
| Interface Description, word 1 |
+--------------+--------------+--------------+--------------+
... ...
+--------------+--------------+--------------+--------------+
| Interface Description , word 8 |
+--------------+--------------+--------------+--------------+
Example 7: IPv6 interface with ifIndex and description
C-Type = 00001011b // Indicates incoming interface
Length = 56 (4 + 4 + 16 + 32)
0 1 2 3
+--------------+--------------+--------------+--------------+
| Interface ifIndex |
+--------------+--------------+--------------+--------------+
| IPv6 address, word 1 |
+--------------+--------------+--------------+--------------+
| IPv6 address, word 2 |
+--------------+--------------+--------------+--------------+
| IPv6 address, word 3 |
+--------------+--------------+--------------+--------------+
| IPv6 address, word 4 |
+--------------+--------------+--------------+--------------+
| Interface Description, word 1 |
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+--------------+--------------+--------------+--------------+
... ...
+--------------+--------------+--------------+--------------+
| Interface Description , word 8 |
+--------------+--------------+--------------+--------------+
Example 8: IPv6 interface with ifIndex
C-Type = 00001010b // Indicates incoming interface
Length = 24 (4 + 4 + 16)
0 1 2 3
+--------------+--------------+--------------+--------------+
| Interface ifIndex |
+--------------+--------------+--------------+--------------+
| IPv6 address, word 1 |
+--------------+--------------+--------------+--------------+
| IPv6 address, word 2 |
+--------------+--------------+--------------+--------------+
| IPv6 address, word 3 |
+--------------+--------------+--------------+--------------+
| IPv6 address, word 4 |
+--------------+--------------+--------------+--------------+
Example 9: IPv6 interface with description
C-Type = 00000011b // Indicates incoming interface
Length = 52 (4 + 16 + 32)
0 1 2 3
+--------------+--------------+--------------+--------------+
| IPv6 address, word 1 |
+--------------+--------------+--------------+--------------+
| IPv6 address, word 2 |
+--------------+--------------+--------------+--------------+
| IPv6 address, word 3 |
+--------------+--------------+--------------+--------------+
| IPv6 address, word 4 |
+--------------+--------------+--------------+--------------+
| Interface Description, word 1 |
+--------------+--------------+--------------+--------------+
... ...
+--------------+--------------+--------------+--------------+
| Interface Description , word 8 |
+--------------+--------------+--------------+--------------+
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Figure 3: Interface Information Object
4.4. Usage
If the incoming interface is unnumbered for the triggering packet
type, then an Interface Information Object of c-type 8 or 9 SHOULD be
included in the ICMPv4 or ICMPv6 Time Exceeded or ICMPv4 or ICMPv6
Destination Unreachable message.
If the triggering packet is IPv4 and the incoming interface has an
IPv4 address, then an Interface Information Object of c-type 4, 5,
12, or 13 MAY be included in the ICMPv4 Time Exceeded and ICMPv4
Destination Unreachable messages.
If the triggering packet is IPv6 incoming interface has an IPv6
address, then an Interface Information Object of c-type 2, 3, 10, or
11 MAY be included in the ICMPv6 Time Exceeded and ICMPv6 Destination
Unreachable messages.
In an ICMP message, more than one Interface Information Object with a
given interface role MUST NOT be included. Multiple Interface
Information Objects, each with a different interface role, MAY be
included.
5. Security Considerations
This extension 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 sub-objects 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.
6. IANA Considerations
IANA should should reserve from the ICMP Extension Object registry: 2
for the Interface Information Object. IANA should reserve from the
Interface ID Object's c-type, bit 0 for the inclusion of the
description sub-object, bit 1 for inclusion of an IPv6 address, bit 2
for inclusion of an IPv4 address, and bit 3 for inclusion of an
ifIndex. Bits 4 and 5 are unallocated and IANA should create a
registry to allocate those with a requirement for standards action.
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Bit 6 and 7 form the Interface Role field. Value 0 should be
allocated for incoming interface; value 1 should be allocated for
outgoing interface. Values 2 and 3 are unallocated and IANA should
allocate those with a requirement for standards action.
Additionally, the Description Sub-Object has a 1 byte charset type
field. IANA should create a registry from it and allocate 0 for
descriptions in ASCII and 1 for descriptions in UTF-8. The remaining
values should be allocated on a first come basis.
7. Acknowledgements
The authors would like to thank Carlos Pignataro, Sasha Vainshtein,
and Joe Touch for their comments and suggestions.
8. References
8.1. Normative References
[I-D.bonica-internet-icmp]
Bonica, R., "Extended ICMP to Support Multi-part
Messages", draft-bonica-internet-icmp-16 (work in
progress), January 2007.
[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.
8.2. 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.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[US-ASCII]
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"Coded Character Set -- 7-bit American Standard Code for
Information Interchange, ANSI X3.4-1986".
Authors' Addresses
Alia K. Atlas (editor)
Google, Inc.
1600 Amphitheatre Parkway
Mountain View, CA 94043
USA
Email: akatlas@google.com
Ronald P. Bonica
Juniper Networks
2251 Corporate Park Drive
Herndon, VA 20171
USA
Email: rbonica@juniper.net
J.R. Rivers
Nuova Systems
Email: jrrivers@nuovasystems.com
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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