MPLS Working Group R. Bonica
Internet-Draft D. Gan
Expires: September 17, 2006 Juniper Networks
D. Tappan
Cisco Systems, Inc.
March 16, 2006
ICMP Extensions for MultiProtocol Label Switching
draft-ietf-mpls-icmp-05
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Copyright (C) The Internet Society (2006).
Abstract
This memo defines an extension to ICMP that permits Label Switching
Routers to append MPLS information to ICMP messages. This extension
has already been widely deployed and this memo is introduced to
describe existing practice.
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Table of Contents
1. Conventions Used In This Document . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Architectural Considerations . . . . . . . . . . . . . . . . . 4
4. Application to TRACEROUTE . . . . . . . . . . . . . . . . . . . 4
5. Disclaimer . . . . . . . . . . . . . . . . . . . . . . . . . . 4
6. MPLS Stack Entry Object . . . . . . . . . . . . . . . . . . . . 5
7. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
9. Normative References . . . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7
Intellectual Property and Copyright Statements . . . . . . . . . . 8
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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].
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" 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 defines an extension to ICMP that permits 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.
The ICMP extensions defined in this document must be preceded by by
an ICMP Extension Structure Header and an ICMP Object Header. Both
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are defined in [4].
3. Architectural Considerations
Only layer 3 information should be included in ICMP messages. MPLS
information can be included only in so much as MPLS participates in
layer 3 routing. Layer 2 information (e.g., ethernet, PPP) should
not be included in ICMP messages.
4. Application to TRACEROUTE
ICMP extensions defined in this memo support enhancements 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 original datagram's MPLS encapsulation
status as it arrived at each node.
Figure 1 contains sample output from an enhanced TRACEROUTE
implementation.
> traceroute 10.100.6.1
traceroute to 10.100.6.1 (10.100.6.1), 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
5. Disclaimer
This memo does not define the general relationship between ICMP and
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MPLS. Sections 2.3 and 2.4 of RFC3032 define this relationship.
The current memo does not define encapsulation specific TTL
manipulation procedures. It defers to Section 5.4 of RFC 3034 [5]
and Section 10 of RFC 3035 [6] in this matter.
When encapsulation specific TTL manipulation procedures defeat the
basic TRACEROUTE mechanism, they will also defeat enhanced TRACEROUTE
implementations.
6. MPLS Stack Entry Object
This section defines an ICMP extention object that can be appended to
the ICMP Time Exceeded and Destination Unreachable messages. 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
Figure 2 depicts the MPLS Stack Entry Object. It must be preceded by
an ICMP Extension Structure Header and an ICMP Object Header. Both
are defined in [4].
In the object payload, 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.
MPLS Stack Entry Class = 1, C-Type = 1.
0 1 2 3
+-------------+-------------+-------------+-------------+
| Label |EXP |S| TTL |
+-------------+-------------+-------------+-------------+
| |
| // Remaining MPLS Stack Entries // |
| |
+-------------+-------------+-------------+-------------+
Figure 2: MPLS Stack Entry Object
Label: 20 bits
Exp: Experimental Use, 3 bits
S: Bottom of Stack, 1 bit
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TTL: Time to Live, 8 bits
7. Security Considerations
This memo presents no security considerations beyond those already
presented by current ICMP applications (e.g., traceroute).
8. IANA Considerations
IANA should should reserve an object class and object type for the
MPLS Stack Entry Object from the ICMP Extension Object registry.
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] Bonica, R., "Extending the Internet Control Message Protocol
(ICMP)", draft-bonica-internet-icmp-01 (work in progress),
January 2006.
[5] Conta, A., Doolan, P., and A. Malis, "Use of Label Switching on
Frame Relay Networks Specification", RFC 3034, January 2001.
[6] 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.
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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
Daniel C. Tappan
Cisco Systems, Inc.
250 Apollo Drive
Chelmsford, MA 01824
US
Email: tappan@cisco.com
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