Internet A. Atlas, Ed.
Internet-Draft BT
Expires: May 19, 2008 R. Bonica
Juniper Networks
JR. Rivers
Nuova Systems
N. Shen
E. Chen
Cisco Systems
Nov 16, 2007
Extending ICMP to Identify the Receiving Interface
draft-atlas-icmp-unnumbered-04
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on May 19, 2008.
Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
This memo defines ICMP extensions, using ICMP multi-part messages,
through which a router or host can explicitly identify the interface
Atlas, et al. Expires May 19, 2008 [Page 1]
Internet-Draft ICMP Unnumbered Nov 2007
upon which an undeliverable datagram anrrived. The incoming
interface can be identified by ifIndex, name, and/or address, as
already used in MIBs and by OSPF. The extensions defined herein are
particularly useful when troubleshooting networks with unnumbered
interfaces, parallel interfaces and/or asymmetric routing.
Table of Contents
1. Conventions Used In This Document . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Applications . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Application to TRACEROUTE . . . . . . . . . . . . . . . . 4
3.2. Policy and MTU Detection . . . . . . . . . . . . . . . . . 4
4. Interface Information Object . . . . . . . . . . . . . . . . . 5
4.1. C-type meaning in an Interface Information Object . . . . 5
4.2. Interface Name Sub-Object . . . . . . . . . . . . . . . . 7
4.3. Interface Information Object Description . . . . . . . . . 8
4.4. Usage . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
8.1. Normative References . . . . . . . . . . . . . . . . . . . 11
8.2. Informative References . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
Intellectual Property and Copyright Statements . . . . . . . . . . 14
Atlas, et al. Expires May 19, 2008 [Page 2]
Internet-Draft ICMP Unnumbered Nov 2007
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 devices use the Internet Control Message Protocol (ICMP) [RFC0792]
(ICMPv6) [RFC4443] to convey control information. In particular,
when an IP device receives a datagram that it cannot forward, it may
send an ICMP message to the datagram's originator. Network operators
and higher level protocols use these ICMP messages to detect and
diagnose network issues.
In the nominal case, the source address of the ICMP message
identifies the interface upon which the non-forwardable datagram
arrived. However, in many cases, the incoming interface is not
identified by the ICMP message at all. Details follow:
According to RFC1812 [RFC1812], when a router generates an ICMP
message, the source address of that ICMP message MUST be one of the
following:
o one of the IP addresses associated with the physical interface
over which the ICMP message is transmitted
o if that interface has no IP addresses associated with it, the
device's router-id or host-id is used instead.
If the following conditions are true, the source address of the ICMP
message identifies the interface upon which the non-forwardable
datagram arrived:
o the device originates an ICMP message through the same interface
upon which the non-forwardable datagram was received.
o that interface is numbered.
However, the transmitting and incoming interfaces may be different
due to an asymmetric return path, which can occur due to asymmetric
link costs, parallel links or ECMP.
For ICMPv6, the asymmetric issues need not be an issue, since there
is more flexibility for ICMPv6, as defined in RFC4443 [RFC4443]. For
responses to messages sent to addresses that aren't the router's, the
source address must be chosen as follows:
Atlas, et al. Expires May 19, 2008 [Page 3]
Internet-Draft ICMP Unnumbered Nov 2007
o the Source Address of the ICMPv6 packet MUST be a unicast address
belonging to the node. The address SHOULD be chosen according to
the rules that would be used to select the source address for any
other packet originated by the node, given the destination address
of the packet. However, it MAY be selected in an alternative way
if this would lead to a more informative choice of address
reachable from the destination of the ICMPv6 packet.
For both ICMP and ICMPv6, when a network uses unnumbered interfaces,
it is not possible to identify the incoming interface. The
extensions defined in this memo permit an ICMP originator to identify
the interface through which the datagram that elicited the ICMP
messages arrived.
Using the extension defined herein, an IP device can explicitly
identify the incoming interface by any or all of the following:
o IPv4 address
o IPv6 address
o name
o ifIndex
Using the extension defined herein, an IP device can explicitly
identify by the above the outgoing interface over which a datagram
would have been forwarded if that datagram had been deliverable.
This can be used for creating a downstream map.
The extensions defined herein use the ICMP multi-part message
framework defined in [RFC4884]. The same backward compatibility
issues that apply to [RFC4884] apply to these extensions.
3. Applications
3.1. Application to TRACEROUTE
ICMP extensions defined in this memo require enhancements ([RFC4884])
and provide additional capability 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 triggering packet arrived,
even when that interface is unnumbered.
3.2. Policy and MTU Detection
A general application would be to identify which outgoing interface
triggered a given function for the original packet. For example, if
Atlas, et al. Expires May 19, 2008 [Page 4]
Internet-Draft ICMP Unnumbered Nov 2007
an ACL drops the packet and Dest Unreachable/Admin Prohibited denies
the packet, being able to identify that might be useful. Another
example would be support PMTU, since this would allow identification
of which outgoing interface can't support a given MTU size.
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 [RFC4884]. 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. If desired, information about a sub-IP member of the
incoming interface can be included. An example of such a sub-IP
member would be a member of an Ethernet Link Aggregation Group that
forms the incoming interface. To minimize the use of extra octets
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 Name Sub-Object, containing a string of no more than
62 octets, MAY be included.
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.
Atlas, et al. Expires May 19, 2008 [Page 5]
Internet-Draft ICMP Unnumbered Nov 2007
Bit 7 6 | 5 4 3 2 1 0
+-------+-------+-------+-------+-------+-------+-------+-------+
| Interface Role| Rsvd | Rsvd | index | IP | Rsvd | 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 : This object describes a sub-IP member of the
incoming interface.
3 : Reserved
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 (leftmost, from highest, 5, to
lowest, 0,).
bit
5 : This bit is reserved for future use and MUST be set to 0 and
MUST be ignored on receipt.
4 : This bit is reserved for future use and MUST be set to 0 and
MUST be ignored on receipt.
3 : When set, this bit indicates the ifIndex of the interface
is included. When clear, the ifIndex is not included.
2 : When set, this indicates an IP address of the interface
is included. When clear, no IP address is included. The
version of the IP packet containing the ICMP message will
indicate the type of IP address. An IPv4 packet will have an
IPv4 address and an IPv6 packet will have an IPv6 address.
1 : This bit is reserved for future use and MUST be set to 0 and
MUST be ignored on receipt.
0 : When set, this indicates an Interface Name Sub-object for
the interface is included. When clear, it is not included.
Figure 1: C-Type for the Interface Information Object
The information/sub-objects MUST be sent and received inside the
Interface Information Object in the order that they are listed in the
final 6-bits included-information field. With the exception of the
Atlas, et al. Expires May 19, 2008 [Page 6]
Internet-Draft ICMP Unnumbered Nov 2007
Interface Name sub-object, the information included does not self-
identify, so this is required to ensure correct parsing.
The sender of an Interface Information Object MUST NOT set the
Interface Role to 3 and an Interface Role value of 3 MUST be ignored
on receipt and the Interface Information Object discarded. It is
valid (though pointless until additional bits are assigned by IANA)
to receive an Interface Information Object where bits 3,2, and 0 are
all 0; this MUST NOT generate a warning or error.
4.2. Interface Name Sub-Object
The Interface Name Sub-Object MUST have a length that is a multiple
of 4 octets and MUST NOT exceed 64 octets. A one octet "charset
type" and a one octet "length" are required and the interface name
can be at most 62 octets long. The interface name SHOULD be the
MIB-II ifName [RFC2863] but MAY be some other human-meaningful name
of the interface. It is useful to rovide the ifName for cross-
correlation with other MIB information and for human-reader
familiarity.
The Interface Name Sub-Object consists of three fields. The first
1-octet field indicates the character set type used by the second
field. The second field contains the length of the Interface name
Sub-object, including the charset type, the length, and the human-
readable name in octets. The maximum valid length is 64 octets. The
length is constrained to ensure there is space for the start of the
original packet and additional information. The third field contains
the human-readable name.
octet 0 1 2 63
+--------------+--------+---..............-----------------+
| charset type | length | interface name octets 1-62 |
+--------------+--------+---..............-----------------+
Figure 2: Interface Name Sub-Object
charset type 0 : This indicates that the human-readable interface
name MUST be provided in the US-ASCII charset [US-ASCII] using the
Default Language [RFC2277].
charset type 1 : This indicates that the human-readable interface
name MUST be provided in the UTF-8 charset [RFC3629] using the
Default Language [RFC2277].
Atlas, et al. Expires May 19, 2008 [Page 7]
Internet-Draft ICMP Unnumbered Nov 2007
4.3. Interface Information Object Description
Figure 3 shows a full ICMPv4 Time Exceeded message, including the
Interface Information Object, which must be preceded by an ICMP
Extension Structure Header and an ICMP Object Header. Both are
defined in [RFC4884].
Figure 4 depicts the Interface Information Object, with two of the
valid permutations.
Although all examples show an Interface Name Sub-object of length 64,
this is only for illustration and depicts the maximum allowable
length.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| unused | Length | unused |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Internet Header + leading octets of original datagram |
| |
| // |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ver=2 | (Reserved) | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length | Class-Num=2 | C-Type=9 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface ifIndex |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Name, 32-bit word 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
... ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Name , 32-bit word 16 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: ICMPv4 Time Exceeded message with Interface Information
Object
Class-Num = 2
Example 1: Unnumbered Interface with ifIndex and interface name
Atlas, et al. Expires May 19, 2008 [Page 8]
Internet-Draft ICMP Unnumbered Nov 2007
C-Type = 00001001b // Indicates incoming interface
Length = 40 (4 + 4 + 32)
0 1 2 3
+--------------+--------------+--------------+--------------+
| Interface ifIndex |
+--------------+--------------+--------------+--------------+
| Interface Name, 32-bit word 1 |
+--------------+--------------+--------------+--------------+
... ...
+--------------+--------------+--------------+--------------+
| Interface Name , 32-bit word 16 |
+--------------+--------------+--------------+--------------+
Example 2: IPv4 interface with IPv4 address,
ifIndex and interface name
C-Type = 00001101b // Indicates incoming interface
Length = 44 (4 + 4 + 4 + 32)
0 1 2 3
+--------------+--------------+--------------+--------------+
| Interface ifIndex |
+--------------+--------------+--------------+--------------+
| IPv4 address |
+--------------+--------------+--------------+--------------+
| Interface Name, 32-bit word 1 |
+--------------+--------------+--------------+--------------+
... ...
+--------------+--------------+--------------+--------------+
| Interface Name, 32-bit word 16 |
+--------------+--------------+--------------+--------------+
Example 3: IPv6 interface with IPv6 address and ifIndex
C-Type = 00001100b // Indicates incoming interface
Length = 24 (4 + 4 + 16)
0 1 2 3
+--------------+--------------+--------------+--------------+
| Interface ifIndex |
+--------------+--------------+--------------+--------------+
| IPv6 address, 32-bit word 1 |
+--------------+--------------+--------------+--------------+
| IPv6 address, 32-bit word 2 |
+--------------+--------------+--------------+--------------+
Atlas, et al. Expires May 19, 2008 [Page 9]
Internet-Draft ICMP Unnumbered Nov 2007
| IPv6 address, 32-bit word 3 |
+--------------+--------------+--------------+--------------+
| IPv6 address, 32-bit word 4 |
+--------------+--------------+--------------+--------------+
Figure 4: Interface Information Object
4.4. Usage
For each interface described by an included Interface Information
Object, these are the rules for the information to be included. If
the interface in question is unnumbered, then the Interface
Information Object SHOULD include the ifIndex and SHOULD NOT include
an IP address. If the interface in question is numbered, then the
Interface Information Object SHOULD include the IP address. Other
fields MAY be included in the Interface Information Object.
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 that will
contain the sub-objects.
For instance, the IP address may be included for all potential
recipients. The ifIndex and interface name could be included as well
if the destination IP address is a management address of the network
that has administrative control of the router.
Another example use case would be where the detailed information in
these extensions may be provided to ICMP destinations within the
local administrative domain, but only traditional information is
provided to 'external' or untrusted ICMP destinations.
Another issue is when a device inside a private region generates an
ICMP message with some of these extensions and that ICMP message will
transit a NAT to reach its destination. A NAT may choose to remove
or overwrite the extensions.
Atlas, et al. Expires May 19, 2008 [Page 10]
Internet-Draft ICMP Unnumbered Nov 2007
6. IANA Considerations
IANA should should reserve from the ICMP Extension Object registry: 2
for the Interface Information Object.
From the Interface ID Object's c-type, IANA should reserve as
follows:
o Bit 0: Interface Name Sub-Object included
o Bit 1: Unallocated - allocatable with Standards Action
o Bit 2: IP address included
o Bit 3: ifIndex include
o Bit 4: Unallocated - allocatable with Standards Action
o Bit 5: Unallocated - allocatable with Standards Action
o Bit 6-7: Interface Role field
* Value 0: Incoming Interface
* Value 1: Outgoing Interface
* Value 2: Incoming Interface - Sub-IP Member
* Value 3: Unallocated - allocatable with Standards Action
Additionally, the Interface Name Sub-Object has a 1 octet charset
type field. IANA should create a registry for it and allocate as
follows:
o 0 : encoded in ASCII
o 1 : encoded in UTF-8
o 2-127: Unallocated - allocatable with Standards Action
o 128-255: Unallocated - allocated on 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
[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.
Atlas, et al. Expires May 19, 2008 [Page 11]
Internet-Draft ICMP Unnumbered Nov 2007
[RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control
Message Protocol (ICMPv6) for the Internet Protocol
Version 6 (IPv6) Specification", RFC 4443, March 2006.
[RFC4884] Bonica, R., Gan, D., Tappan, D., and C. Pignataro,
"Extended ICMP to Support Multi-Part Messages", RFC 4884,
April 2007.
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.
[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".
Authors' Addresses
Alia K. Atlas (editor)
BT
Email: alia.atlas@bt.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
Atlas, et al. Expires May 19, 2008 [Page 12]
Internet-Draft ICMP Unnumbered Nov 2007
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
Atlas, et al. Expires May 19, 2008 [Page 13]
Internet-Draft ICMP Unnumbered Nov 2007
Full Copyright Statement
Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Acknowledgment
Funding for the RFC Editor function is provided by the IETF
Administrative Support Activity (IASA).
Atlas, et al. Expires May 19, 2008 [Page 14]
