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Versions: 00 01 02 03 04 05 06 07 08 RFC 4950
MPLS Working Group R. Bonica
Internet-Draft D. Gan
Expires: February 3, 2006 Juniper Networks
D. Tappan
Cisco Systems, Inc.
August 2, 2005
ICMP Extensions for MultiProtocol Label Switching
draft-ietf-mpls-icmp-03
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Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This memo proposes extensions to ICMP that permit Label Switching
Routers to append MPLS information to ICMP messages.
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Table of Contents
1. Conventions Used In This Document . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Application to TRACEROUTE . . . . . . . . . . . . . . . . . . 5
4. Disclaimer . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5.1 Common Header . . . . . . . . . . . . . . . . . . . . . . 8
5.2 Object Header . . . . . . . . . . . . . . . . . . . . . . 8
5.3 MPLS Stack Entry Object Class . . . . . . . . . . . . . . 9
5.4 Extended Payload Object Class . . . . . . . . . . . . . . 10
6. Backward Compatibility . . . . . . . . . . . . . . . . . . . . 11
7. Security Considerations . . . . . . . . . . . . . . . . . . . 12
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
9. Normative References . . . . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 13
Intellectual Property and Copyright Statements . . . . . . . . 15
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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 [1].
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2. Introduction
IP routers use the Internet Control Message Protocol (ICMP) [2] to
convey control information to source hosts. Network operators use
this information to diagnose routing problems.
When a router receives an undeliverable IP datagram, it can send an
ICMP message to the host that originated the datagram. The ICMP
message indicates why the datagram could not be delivered. It also
contains the IP header and leading payload octets of the "original
datagram".
In this document, the term "original datagram" refers to the datagram
to which the ICMP message is a response.
MPLS Label Switching Routers (LSR) also use ICMP to convey control
information to source hosts. Sections 2.3 and 2.4 of RFC 3032 [3]
describe the interaction between MPLS and ICMP.
When an LSR receives an undeliverable MPLS encapsulated datagram, it
removes the entire MPLS label stack, exposing the previously
encapsulated IP datagram. The LSR then submits the IP datagram to an
error processing module. Error processing can include ICMP message
generation.
The ICMP message indicates why the original datagram could not be
delivered. It also contains the IP header and leading octets of the
original datagram.
The ICMP message, however, contains no information regarding the MPLS
label stack that encapsulated the original datagram when it arrived
at the LSR. This omission is significant because the LSR would have
routed the original datagram based upon information contained by the
MPLS label stack.
This memo proposes extensions to ICMP that permit an LSR to append
MPLS label stack information to ICMP messages. ICMP messages
regarding MPLS encapsulated datagrams SHOULD include the MPLS label
stack, as it arrived at the router that is sending the ICMP message.
The ICMP message MUST also include the IP header and leading payload
octets of the original datagram.
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3. Application to TRACEROUTE
ICMP extensions defined in this memo support enhancements to
TRACEROUTE. The enhanced TRACEROUTE, like older implementations,
indicates which nodes the original datagram visited en route to its
destination. It differs from older implementations in that it also
indicates the original datagrams MPLS encapsulation status as it
arrived at each node.
Figure 1 contains sample output from an enhanced TRACEROUTE
implementation.
> traceroute 100.100.6.1
traceroute to 100.100.6.1 (100.100.6.1), 30 hops max, 40 byte packets
1 10.1.1.2 (10.1.1.2) 0.661 ms 0.618 ms 0.579 ms
2 10.1.12.2 (10.1.12.2) 0.861 ms 0.718 ms 0.679 ms
MPLS Label=100048 Exp=0 TTL=1 S=1
3 10.1.24.2 (10.1.24.2) 0.822 ms 0.731 ms 0.708 ms
MPLS Label=100016 Exp=0 TTL=1 S=1
4 10.100.6.1 (10.100.6.1) 0.961 ms 8.676 ms 0.875 ms
Figure 1: Enhanced TRACEROUTE Sample Output
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4. Disclaimer
This memo does not define the general relationship between ICMP and
MPLS. Sections 2.3 and 2.4 of RFC3032 define this relationship.
Specifically, this document defers to RFC3032 with respect to the
following issues:
- conditions upon which an LSR emits ICMP messages
- handling of ICMP messages bound for hosts that are identified by
private addresses
The current memo does not define encapsulation specific TTL
manipulation procedures. It defers to Section 5.4 of RFC 3034 [4]
and Section 10 of RFC 3035 [5] in this matter.
When encapsulation specific TTL manipulation procedures defeat the
basic TRACEROUTE mechanism, they will also defeat enhanced TRACEROUTE
implementations.
The current memo does not address extensions to ICMPv6. These should
be addressed in a separate draft.
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5. Syntax
This section defines a data structure that an LSR can append to
selected ICMP messages. The data structure contains the MPLS label
stack that encapsulated the original datagram when it arrived at the
LSR.
In theory, the data structure defined herein can be appended to the
following ICMP message types:
Destination Unreachable
Time Exceeded
Parameter Problem
Source Quench
Redirect
However, in practice, it would only be useful when appended to the
Destination Unreachable and Time Exceeded messages.
According to RFC-792, bytes 0 through 19 of any ICMP message contain
a header whose format is analogous to that of the IP datagram. Bytes
20 through 23 contain an ICMP message type, code and checksum. Bytes
24 through 27 contain message specific data.
Also according to RFC-792, the final field contained by each of the
ICMP message types listed above begins at byte 28. It reflects the
IP header and leading 64 bits of the original datagram. RFC 1812 [6]
recommends that this final field be extended to include as much of
the original datagram as possible.
When an LSR appends the data structure defined herein to an ICMP
message, the final field of the ICMP message body MUST contain the
first 128 octets of the original datagram. At least 20 of these 128
octets represent the IP header of the original datagram.
If the original datagram was shorter than 128 octets, the final field
MUST be padded with 0's.
When an LSR appends the data structure defined herein to an ICMP
message, the ICMP "total length" MUST be adjusted appropriately to
include the data structure.
The data structure defined in this section consists of a common
header followed by object instances. Each object instance consists
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of an object header plus contents.
Currently, two object classes are defined. One object class contains
an entire MPLS label stack, formatted exactly as it was when it
arrived at the LSR that sends the ICMP message. The other contains
some portion of the original datagram that could not be included in
the final field of the ICMP message body (i.e., the octet 129 and
beyond).
Both object classes are optional.
In the future, additional object classes may be defined.
5.1 Common Header
0 1 2 3
+-------------+-------------+-------------+-------------+
| Vers | (Reserved) | Checksum |
+-------------+-------------+-------------+-------------+
Figure 2: Common Header
The fields in the common header are as follows:
Vers: 4 bits
ICMP extension version number. This is version 2.
Checksum: 16 bits
The one's complement of the one's complement sum of the data
structure, with the checksum field replaced by zero for the
purpose of computing the checksum. An all-zero value means that
no checksum was transmitted.
If the checksum field contains a value other than described above,
the ICMP message does not include the extensions described in this
memo. This, however, does not imply that the ICMP message is
malformed. It may be in strict compliance with RFC-1812.
Reserved: Must be set to 0.
5.2 Object Header
Every object consists of one or more 32-bit words with a one-word
header. The following is the format of the one-word header:
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+-------------+-------------+-------------+-------------+
| Length | Class-Num | C-Type |
+-------------+-------------+-------------+-------------+
| |
| // (Object contents) // |
| |
+-------------+-------------+-------------+-------------+
Figure 3: Object Header
An object header has the following fields:
Length: 16 bits
Length of the object, measured in octets, including the object
header and object contents.
Class-Num: 8 bits
Identifies object class.
C-Type: 8 bits
Identifies object sub-type.
5.3 MPLS Stack Entry Object Class
A single instance of the MPLS Entry Object class represents the
entire MPLS label stack, formatted exactly as it was when it arrived
at the LSR that sends the ICMP message
In the illustration below, octets 0-3 depict the first member of the
MPLS label stack. Each remaining member of the MPLS label stack is
represented by another 4 octets that share the same format.
Syntax follows:
MPLS Stack Entry Class = 1, C-Type = 1.
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0 1 2 3
+-------------+-------------+-------------+-------------+
| Label |EXP |S| TTL |
+-------------+-------------+-------------+-------------+
| |
| // Remaining MPLS Stack Entries // |
| |
+-------------+-------------+-------------+-------------+
Figure 4: MPLS Stack Entry Object Class
Label: 20 bits
Exp: Experimental Use, 3 bits
S: Bottom of Stack, 1 bit
TTL: Time to Live, 8 bits
5.4 Extended Payload Object Class
An instance of the Extended Payload Object class represents some
portion of the original datagram that could not be fit in the final
field of the ICMP message body (i.e., octets beyond 128).
Syntax follows:
MPLS Stack Entry Class = 2, C-Type = 1.
0 1 2 3
+-------------+-------------+-------------+-------------+
| |
| // Additional bytes of original datagram // |
| |
+-------------+-------------+-------------+-------------+
Figure 5: Extended Payload Object Class
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6. Backward Compatibility
ICMP extensions proposed in this document MUST be backward compatible
with the syntax described in RFC-792. Extensions proposed in this
memo MUST NOT change or deprecate any field defined in RFC-792.
The extensions defined herein are in keeping with the spirit, if not
the letter of RFC-1812. In order to support IP-in-IP tunneling, RFC-
1812 extends the final field of selected ICMP messages to include a
greater portion of the original datagram. Unfortunately, it extends
this field to a variable length without adding a length attribute.
This memo binds the length of that final field to an arbitrarily
large value (128 octets). Fixing the length of that field
facilitates extension of the ICMP message. An additional object is
provided through which octets 129 and beyond can be appended to the
ICMP message.
As few datagrams contain L3 or L4 header information beyond octet
128, it is unlikely that the extensions described herein will disable
any applications that rely upon RFC-1812 style ICMP messages.
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7. Security Considerations
This memo presents no security considerations beyond those already
presented by current ICMP applications (e.g., traceroute).
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8. IANA Considerations
IANA should establish a registry of ICMP extention classes and class-
sub-types.
9. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Postel, J., "Internet Control Message Protocol", STD 5, RFC 792,
September 1981.
[3] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., Farinacci, D.,
Li, T., and A. Conta, "MPLS Label Stack Encoding", RFC 3032,
January 2001.
[4] Conta, A., Doolan, P., and A. Malis, "Use of Label Switching on
Frame Relay Networks Specification", RFC 3034, January 2001.
[5] Davie, B., Lawrence, J., McCloghrie, K., Rosen, E., Swallow, G.,
Rekhter, Y., and P. Doolan, "MPLS using LDP and ATM VC
Switching", RFC 3035, January 2001.
[6] Baker, F., "Requirements for IP Version 4 Routers", RFC 1812,
June 1995.
Authors' Addresses
Ronald P. Bonica
Juniper Networks
2251 Corporate Park Drive
Herndon, VA 20171
US
Email: rbonica@juniper.net
Der-Hwa Gan
Juniper Networks
1194 N. Mathilda Ave.
Sunnyvale, CA 94089
US
Email: dhg@juniper.net
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Daniel C. Tappan
Cisco Systems, Inc.
250 Apollo Drive
Chelmsford, MA 01824
US
Email: tappan@cisco.com
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