Internet Engineering Task Force (IETF) A. Atlas, Ed.
Request for Comments: 5837 BT
Category: Standards Track R. Bonica, Ed.
ISSN: 2070-1721 Juniper Networks
C. Pignataro, Ed.
N. Shen
Cisco Systems
JR. Rivers
Consultant
April 2010
Extending ICMP for Interface and Next-Hop Identification
Abstract
This memo defines a data structure that can be appended to selected
ICMP messages. The ICMP extension defined herein can be used to
identify any combination of the following: the IP interface upon
which a datagram arrived, the sub-IP component of an IP interface
upon which a datagram arrived, the IP interface through which the
datagram would have been forwarded had it been forwardable, and the
IP next hop to which the datagram would have been forwarded.
Devices can use this ICMP extension to identify interfaces and their
components by any combination of the following: ifIndex, IPv4
address, IPv6 address, name, and MTU. ICMP-aware devices can use
these extensions to identify both numbered and unnumbered interfaces.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc5837.
Atlas, et al. Standards Track [Page 1]RFC 5837 ICMP Unnumbered April 2010
Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used In This Document . . . . . . . . . . . . . . 5
3. Applications . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Application to Traceroute . . . . . . . . . . . . . . . . 5
3.2. Policy and MTU Detection . . . . . . . . . . . . . . . . . 6
4. Interface Information Object . . . . . . . . . . . . . . . . . 6
4.1. C-Type Meaning in an Interface Information Object . . . . 7
4.2. Interface IP Address Sub-Object . . . . . . . . . . . . . 9
4.3. Interface Name Sub-Object . . . . . . . . . . . . . . . . 10
4.4. Interface Information Object Examples . . . . . . . . . . 10
4.5. Usage . . . . . . . . . . . . . . . . . . . . . . . . . . 13
5. Network Address Translation Considerations . . . . . . . . . . 14
6. Security Considerations . . . . . . . . . . . . . . . . . . . 14
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
9.1. Normative References . . . . . . . . . . . . . . . . . . . 16
9.2. Informative References . . . . . . . . . . . . . . . . . . 16
Atlas, et al. Standards Track [Page 2]RFC 5837 ICMP Unnumbered April 2010
1. Introduction
IP devices use the Internet Control Message Protocol (ICMPv4
[RFC0792] and ICMPv6 [RFC4443]) to convey control information. In
particular, when an IP device receives a datagram that it cannot
process, 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 simplest case, the source address of the ICMP message
identifies the interface upon which the datagram arrived. However,
in many cases, the incoming interface is not identified by the ICMP
message at all. Details follow:
According to [RFC1812], when a router generates an ICMPv4 message,
the source address of that message MUST be one of the following:
o one of the IP addresses associated with the physical interface
over which the ICMPv4 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 all of the following conditions are true, the source address of
the ICMPv4 message identifies the interface upon which the original
datagram arrived:
o the device sends an ICMPv4 message through the same interface upon
which the original datagram was received
o that interface is numbered
However, the incoming and outgoing interfaces may be different due to
an asymmetric return path, which can occur due to asymmetric link
costs, parallel links, or Equal Cost Multipath (ECMP).
Similarly, [RFC1122] provides guidance for source address selection
for multihomed IPv4 hosts. These recommendations, like those stated
above, do not always cause the source address of an ICMPv4 message to
identify the incoming interface.
ICMPv6 is somewhat more flexible. [RFC4443] states that for
responses to messages sent to a non-local interface, the source
address must be chosen as follows:
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
Atlas, et al. Standards Track [Page 3]RFC 5837 ICMP Unnumbered April 2010
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.
When a datagram that cannot be processed arrives on an unnumbered
interface, neither ICMPv4 nor ICMPv6 is currently capable of
identifying the incoming interface. Even when an ICMP message is
generated such that the ICMP source address identifies the incoming
interface, the receiver of that ICMP message has no way of knowing if
this is the case. ICMP extensions are required to explicitly
identify the incoming interface.
Using the extension defined herein, a device can explicitly identify
the incoming IP interface or its sub-IP components by any combination
of the following:
o ifIndex
o IPv4 address
o IPv6 address
o name
o MTU
The interface name SHOULD be identical to the first 63 octets of the
ifName, as defined in [RFC2863]. The ifIndex is also defined in
[RFC2863].
Using the same extension, 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.
The next-hop IP address, to which the datagram would have been
forwarded, can also be identified using this same extension. This
information can be used for creating a downstream map. The next-hop
information may not always be available. There are corner-cases
where it doesn't exist and there may be implementations where it is
not practical to provide this information. This specification
provides an encoding for providing the next-hop IP address when it is
available.
The extension defined herein uses the ICMP multi-part message
framework defined in [RFC4884]. The same backward compatibility
issues that apply to [RFC4884] apply to this extension.
Atlas, et al. Standards Track [Page 4]RFC 5837 ICMP Unnumbered April 2010
2. 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 RFC 2119 [RFC2119].
3. Applications
3.1. Application to Traceroute
ICMP extensions defined in this memo provide additional capability to
traceroute. An enhanced traceroute application, like older
implementations, identifies nodes that a datagram visited en route to
its destination. It differs from older implementations in that it
can explicitly identify the following at each node:
o the IP interface upon which a datagram arrived
o the sub-IP component of an IP interface upon which a datagram
arrived
o the IP interface through which the datagram would have been
forwarded had it been forwardable
o the IP next hop to which the datagram would have been forwarded
Enhanced traceroute applications can identify the above listed
entities by:
o ifIndex
o IPv4 address
o IPv6 address
o name
o MTU
The ifIndex can be utilized within a management domain to map to an
actual interface, but it is also valuable in public applications.
The ifIndex can be used as an opaque token to discern whether or not
two ICMP messages generated from the same router involve the same
interface.
Atlas, et al. Standards Track [Page 5]RFC 5837 ICMP Unnumbered April 2010
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
an access control list (ACL) drops the packet and Dest Unreachable/
Admin Prohibited denies the packet, being able to identify the
outgoing interface might be useful. Another example would be to
support Path MTU Discovery (PMTUD), since this would allow
identification of which outgoing interface can't support a given MTU
size. For example, knowledge of the problematic interface would
allow an informed request for reconfiguration of the MTU of that
interface.
4. Interface Information Object
This section defines the Interface Information Object, an ICMP
extension object with a Class-Num (Object Class Value) of 2 that can
be appended to the following messages:
o ICMPv4 Time Exceeded
o ICMPv4 Destination Unreachable
o ICMPv4 Parameter Problem
o ICMPv6 Time Exceeded
o ICMPv6 Destination Unreachable
For reasons described in [RFC4884], this extension cannot be appended
to any of the currently defined ICMPv4 or ICMPv6 messages other than
those listed above.
The extension defined herein MAY be appended to any of the above
listed messages and SHOULD be appended whenever required to identify
an unnumbered interface and when local policy or security
considerations do not supersede this requirement.
A single ICMP message can contain as few as zero and as many as four
instances of the Interface Information Object. It is illegal if it
contains more than four instances, because that means that an
interface role is used more than once (see Section 4.5).
A single instance of the Interface Information Object can provide
information regarding any one of the following interface roles:
o the IP interface upon which a datagram arrived
Atlas, et al. Standards Track [Page 6]
RFC 5837 ICMP Unnumbered April 2010
o the sub-IP component of an IP interface upon which a datagram
arrived
o the IP interface through which the datagram would have been
forwarded had it been forwardable
o the IP next hop to which the datagram would have been forwarded
The following are examples of sub-IP components of IP interfaces upon
which a datagram might arrive:
o Ethernet Link Aggregation Group Member
o Multilink PPP bundle member
o Multilink frame relay bundle member
To minimize the number of octets required for this extension, there
are four different pieces of information that can appear in an
Interface Information Object.
1. The ifIndex of the interface of interest MAY be included. This
is the 32-bit ifIndex assigned to the interface by the device as
specified by the Interfaces Group MIB [RFC2863].
2. An IP Address Sub-Object MAY be included if either of the
following conditions is true: a) the eliciting datagram is IPv4
and the identified interface has at least one IPv4 address
associated with it, or b) the eliciting datagram is IPv6 and the
identified interface has at least one IPv6 address associated
with it. The IP Address Sub-Object is described in Section 4.2
of this memo.
3. An Interface Name Sub-Object, containing a string of no more than
63 octets, MAY be included. That string, as specified in
Section 4.3, is the interface name and SHOULD be the MIB-II
ifName [RFC2863], but MAY be some other human-meaningful name of
the interface.
4. A 32-bit unsigned integer reflecting the MTU MAY be included.
4.1. C-Type Meaning in an Interface Information Object
For this object, the C-Type [RFC4884] is used to indicate both the
role of the interface and the information that is included. This is
illustrated in Figure 1.
Atlas, et al. Standards Track [Page 7]RFC 5837 ICMP Unnumbered April 2010
Bit 0 1 2 3 4 5 6 7
+-------+-------+-------+-------+-------+-------+-------+-------+
| Interface Role| Rsvd1 | Rsvd2 |ifIndex| IPAddr| name | MTU |
+-------+-------+-------+-------+-------+-------+-------+-------+
Figure 1: C-Type for the Interface Information Object
The following are bit-field definitions for C-Type:
Interface Role (bits 0-1): These bits indicates the role of the
interface being identified. The enumerated values are given below:
Value 0: This object describes the IP interface upon which a
datagram arrived
Value 1: This object describes the sub-IP component of an IP
interface upon which a datagram arrived
Value 2: This object describes the IP interface through which the
datagram would have been forwarded had it been
forwardable
Value 3: This object describes the IP next hop to which the
datagram would have been forwarded
Reserved 1 (bit 2): This bit is reserved for future use and MUST be
set to 0 and MUST be ignored on receipt.
Reserved 2 (bit 3): This bit is reserved for future use and MUST be
set to 0 and MUST be ignored on receipt.
ifIndex (bit 4) : When set, the 32-bit ifIndex of the interface is
included. When clear, the ifIndex is not included.
IP Addr (bit 5) : When set, an IP Address Sub-Object is present.
When clear, an IP Address Sub-Object is not present. The IP Address
Sub-Object is described in Section 4.2 of this memo.
Interface Name (bit 6): When set, an Interface Name Sub-Object is
included. When clear, it is not included. The Name Sub-Object is
described in Section 4.3 of this memo.
MTU (bit 7): When set, a 32-bit integer representing the MTU is
present. When clear, this 32-bit integer is not present.
The information included does not self-identify, so this
specification defines a specific ordering for sending the information
that must be followed.
Atlas, et al. Standards Track [Page 8]RFC 5837 ICMP Unnumbered April 2010
If bit 4 (ifIndex) is set, then the 32-bit ifIndex MUST be sent
first. If bit 5 (IP Address) is set, an IP Address Sub-Object MUST
be sent next. If bit 6 (Name) is set, an Interface Name Sub-Object
MUST be sent next. If bit 7 is set, an MTU MUST be sent next. The
information order is thus: ifIndex, IP Address Sub-Object, Interface
Name Sub-Object, and MTU. Any or all pieces of information may be
present or absent, as indicated by the C-Type. Any data that follows
these optional pieces of information MUST be ignored.
It is valid (though pointless until additional bits are assigned by
IANA) to receive an Interface Information Object where bits 4, 5, 6,
and 7 are all 0; this MUST NOT generate a warning or error.
4.2. Interface IP Address Sub-Object
Figure 2 depicts the Interface Address Sub-Object:
0 31
+-------+-------+-------+-------+
| AFI | Reserved |
+-------+-------+-------+-------+
| IP Address ....
Figure 2: Interface Address Sub-Object
The IP Address Sub-Object contains the following fields:
o Address Family Identifier (AFI): This 16-bit bit field identifies
the type of address represented by the IP Address field. It also
determines the length of that field and the length of the entire
sub-object. Values for this field represent a subset of values
found in the IANA registry of Address Family Numbers (available
from <http://www.iana.org>). Valid values are 1 (representing a
32-bit IPv4 address) and 2 (representing a 128-bit IPv6 address).
o Reserved: This 16-bit field MUST be set to zero and ignored upon
receipt.
o IP Address: This variable-length field represents an IP address
associated with the identified interface.
If the eliciting datagram was IPv4, the IP Interface Sub-Object MUST
represent an IPv4 address. Likewise, if the eliciting datagram was
IPv6, the IP Interface Sub-Object MUST represent an IPv6 address.
Atlas, et al. Standards Track [Page 9]RFC 5837 ICMP Unnumbered April 2010
4.3. Interface Name Sub-Object
Figure 3 depicts the Interface Name Sub-Object:
octet 0 1 63
+--------+-----------................-----------------+
| length | interface name octets 1-63 |
+--------+-----------................-----------------+
Figure 3: 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.
The Length field represents the length of the Interface Name Sub-
Object, including the length and the interface 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 second field contains the human-readable interface name. The
interface name SHOULD be the full MIB-II ifName [RFC2863], if less
than 64 octets, or the first 63 octets of the ifName, if the ifName
is longer. The interface name MAY be some other human-meaningful
name of the interface. It is useful to provide the ifName for cross-
correlation with other MIB information and for human-reader
familiarity. The interface name MUST be padded with ASCII NULL
characters if the object would not otherwise terminate on a 4-octet
boundary.
The interface name MUST be represented in the UTF-8 charset [RFC3629]
using the Default Language [RFC2277].
4.4. Interface Information Object Examples
Figure 4 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].
Although examples show an Interface Name Sub-Object of length 64,
this is only for illustration and depicts the maximum allowable
length.
Atlas, et al. Standards Track [Page 10]RFC 5837 ICMP Unnumbered April 2010
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=00001010b |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface ifIndex |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Name Sub-Object, 32-bit word 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
... ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Name Sub-Object, 32-bit word 16 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: ICMPv4 Time Exceeded Message with Interface Information
Object
Figure 5 depicts an Interface Information Object representing an
incoming interface identified by ifIndex and Name.
Class-Num = 2
C-Type = 00001010b // Indicates incoming interface
Length = 72 (4 + 4 + 64)
0 1 2 3
+--------------+--------------+--------------+--------------+
| Interface ifIndex |
+--------------+--------------+--------------+--------------+
| Length | Name, word 1 |
+--------------+--------------+--------------+--------------+
... ...
+--------------+--------------+--------------+--------------+
| Name, word 16 |
+--------------+--------------+--------------+--------------+
Figure 5: Incoming Interface: By ifIndex and Name
Atlas, et al. Standards Track [Page 11]RFC 5837 ICMP Unnumbered April 2010
Figure 6 depicts an Interface Information Object representing an
incoming interface identified by ifIndex, IPv4 Address, and Name.
Class-Num = 2
C-Type = 00001110b // Indicates incoming interface
Length = 80 (4 + 4 + 8 + 64)
0 1 2 3
+--------------+--------------+--------------+--------------+
| Interface ifIndex |
+--------------+--------------+--------------+--------------+
| AFI | Reserved |
+--------------+--------------+--------------+--------------+
| IPv4 address |
+--------------+--------------+--------------+--------------+
| Length | Name, word 1 |
+--------------+--------------+--------------+--------------+
... ...
+--------------+--------------+--------------+--------------+
| Name, word 16 |
+--------------+--------------+--------------+--------------+
Figure 6: Incoming Interface: by ifIndex, IPv4 Address, and Name
Figure 7 depicts an Interface Information Object representing an
incoming interface identified by ifIndex and IPv6 Address.
Class-Num = 2
C-Type = 00001100b // Indicates incoming interface
Length = 28 (4 + 4 + 20)
0 1 2 3
+--------------+--------------+--------------+--------------+
| Interface ifIndex |
+--------------+--------------+--------------+--------------+
| AFI | Reserved |
+--------------+--------------+--------------+--------------+
| IPv6 address, 32-bit word 1 |
+--------------+--------------+--------------+--------------+
| IPv6 address, 32-bit word 2 |
+--------------+--------------+--------------+--------------+
| IPv6 address, 32-bit word 3 |
+--------------+--------------+--------------+--------------+
| IPv6 address, 32-bit word 4 |
+--------------+--------------+--------------+--------------+
Figure 7: Incoming Interface: By ifIndex and IPv6 Address
Atlas, et al. Standards Track [Page 12]RFC 5837 ICMP Unnumbered April 2010
Figure 8 depicts an Interface Information Object representing an
outgoing interface identified by ifIndex and Name.
Class-Num = 2
C-Type = 10001010b // Indicates outgoing interface
Length = 72 (4 + 4 + 64)
0 1 2 3
+--------------+--------------+--------------+--------------+
| Interface ifIndex |
+--------------+--------------+--------------+--------------+
| Length | Name, word 1 |
+--------------+--------------+--------------+--------------+
... ...
+--------------+--------------+--------------+--------------+
| Name, word 16 |
+--------------+--------------+--------------+--------------+
Figure 8: Outgoing Interface: By ifIndex and Name
4.5. Usage
Multiple Interface Information Objects MAY be included within a
single ICMP message, provided that each Interface Information Object
specifies a unique role. A single ICMP message MUST NOT contain two
Interface Information Objects that specify the same role.
ifIndex, MTU, and name information MAY be included whenever it is
available; more than one instance of each of these three information
elements MUST NOT be included per Interface Information Object.
A single instance of IP Address information MAY be included in an
Interface Information Object under the following circumstances:
o if the eliciting datagram is IPv4 and an IPv4 address is
associated with the identified interface. In this case, if an IP
Address Sub-Object is included, it must specify an IPv4 address.
o if the eliciting datagram is IPv6 and an IPv6 address is
associated with the identified interface. In this case, if an IP
Address Sub-Object is included, it must specify an IPv6 address.
In all other circumstances, IP address information MUST NOT be
included.
An ICMP message that does not conform to these rules and contains
multiple instances of the same information is considered illegal;
specifically, an ICMP message containing more than one Interface
Atlas, et al. Standards Track [Page 13]RFC 5837 ICMP Unnumbered April 2010
Information Object with the same role, as well as an ICMP message
containing a duplicate information element in a given role are
considered illegal. If such an illegal ICMP message is received, it
MUST be silently discarded.
5. Network Address Translation Considerations
[RFC5508] encourages Traditional IP Network Address Translators
(Traditional NATs; see [RFC3022]) to support ICMP extension objects.
This document defines an ICMP extension that includes IP addresses
and therefore contains realm-specific information, and consequently
describes possible NAT behaviors in the presence of these extensions.
NAT devices MUST NOT translate or overwrite the ICMP extensions
described herein. That is, they MUST either remove the extension
entirely or pass it unchanged.
It is conceivable that a NAT device might translate an ICMP header
without translating the extension defined herein. In this case, the
ICMP message might contain two instances of the same address, one
translated and the other untranslated. Therefore, application
developers should not assume addresses in the extension are of the
same realm as the addresses in the datagram's header.
It also is conceivable that a NAT device might translate an ICMPv4
message into ICMPv6 or vice versa. If that were to occur,
applications might receive ICMPv6 messages that contain IP Address
Sub-Objects that specify IPv4 addresses. Likewise, applications
might receive ICMPv4 messages that contain IP Address Sub-Objects
that specify IPv6 addresses.
6. Security Considerations
This extension can provide the user of traceroute with additional
network information that is not currently available. Implementations
SHOULD provide configuration switches that suppress the generation of
this extension based upon role (i.e., incoming interface, outgoing
interface, sub-IP data). Implementations SHOULD also provide
configuration switches that conceal various types of information
(e.g., ifIndex, interface name).
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. The implementation of policy
controls could also be based upon the mechanisms described in
[TRACEROUTE-EXT] for those limited cases supported.
Atlas, et al. Standards Track [Page 14]
RFC 5837 ICMP Unnumbered April 2010
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.
The intended field of use for the extensions defined in this document
is administrative debugging and troubleshooting. The extensions
herein defined supply additional information in ICMP responses.
These mechanisms are not intended to be used in non-debugging
applications.
This document does not specify an authentication mechanism for the
extension that it defines. Application developers should be aware
that ICMP messages and their contents are easily spoofed.
7. IANA Considerations
IANA has reserved 2 for the Interface Information Object from the
ICMP Extension Object Classes registry available from
<http://www.iana.org>.
From the Interface Information Object's C-Type, IANA has reserved
values as follows:
o Bit 0-1: Interface Role field
o Bit 2: Unallocated - allocatable with Standards Action
o Bit 3: Unallocated - allocatable with Standards Action
o Bit 4: ifIndex included
o Bit 5: IP Address Sub-Object included
o Bit 6: Name Sub-Object included
o Bit 7: MTU included
IANA has reserved the following values for Interface Role:
o Value 0: Incoming IP Interface
o Value 1: Sub-IP Component of Incoming IP Interface
Atlas, et al. Standards Track [Page 15]
RFC 5837 ICMP Unnumbered April 2010
o Value 2: Outgoing IP Interface
o Value 3: IP Next Hop
8. Acknowledgments
The authors would like to thank Sasha Vainshtein, Enke Chen, and Joe
Touch for their comments and suggestions. They would also like to
thank Dr. Ali Assefi.
9. References
9.1. 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.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[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.
9.2. Informative References
[RFC1122] Braden, R., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122,
October 1989.
[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.
Atlas, et al. Standards Track [Page 16]RFC 5837 ICMP Unnumbered April 2010
[RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP
Network Address Translator (Traditional NAT)",
RFC 3022, January 2001.
[RFC5508] Srisuresh, P., Ford, B., Sivakumar, S., and S.
Guha, "NAT Behavioral Requirements for ICMP",
BCP 148, RFC 5508, April 2009.
[TRACEROUTE-EXT] Shen, N., Pignataro, C., Asati, R., and E. Chen,
"UDP Traceroute Message Extension", Work in
Progress, June 2008.
Atlas, et al. Standards Track [Page 17]RFC 5837 ICMP Unnumbered April 2010
Authors' Addresses
Alia K. Atlas (editor)
BT
EMail: alia.atlas@bt.com
Ronald P. Bonica (editor)
Juniper Networks
2251 Corporate Park Drive
Herndon, VA 20171
USA
EMail: rbonica@juniper.net
Carlos Pignataro (editor)
Cisco Systems
7200-12 Kit Creek Road
PO Box 14987
Research Triangle Park, NC 27709
USA
EMail: cpignata@cisco.com
Naiming Shen
Cisco Systems
225 West Tasman Drive
San Jose, CA 95134
USA
EMail: naiming@cisco.com
JR. Rivers
Consultant
EMail: jrrivers@yahoo.com
Atlas, et al. Standards Track [Page 18]
