MPLS Extensions to ICMP

1
MPLS Extensions to ICMP

• Ron Bonica
• Der-Hwa Gan
• Dan Tappan

2
Plain Old ICMP (RFC 792)

• When a router receives an IP datagram that it
  cant forward, it sends an ICMP message to the
  datagrams originator
• The ICMP message indicates why the datagram
  couldnt be delivered
• E.g., Time Expired, Destination Unreachable
• The ICMP message also contains the IP header and
  leading 8 octets of the original datagram
• RFC 1812 extends this to as many bytes as
  possible

3
ICMP Post MPLS (RFC 3032)

• When an LSR receives an MPLS encapsulated
  datagram that it cant deliver
• It removes entire MPLS labels stack
• It sends an ICMP message to datagrams originator
• The ICMP message indicates why the datagram
  couldnt be delivered (e.g., time expired,
  destination unreachable)
• The ICMP message also contains the IP header and
  leading 8 octets of the original datagram
• RFC 1812 extends this to as many bytes as
  possible

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ICMP Post MPLS Omissions

• The ICMP message contains no information
  regarding the MPLS stack that encapsulated the
  datagram when it arrived at the LSR
• This is a significant omission because
• The LSR tried to forward the datagram based upon
  that label stack
• Resulting ICMP message may be confusing

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Confusing ICMP Messages

• ICMP Destination Unreachable
• Message contains IP header of original datagram
• Router sending ICMP message has an IP route to
  the original datagrams destination
• Original datagram couldnt be delivered because
  MPLS forwarding path was broken
• ICMP Time Expired
• Message contains IP header of original datagram
• TTL value in IP header is greater than 1
• TTL expired on MPLS header. ICMP Message contains
  IP header of original datagram

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Proposal

• Fix Final Field of ICMP message (IP header
  leading payload bytes) to 128 bytes (0 padded).
• Need to do this because it lacks a length
  attribute
• Append extensions to that
• Common Extension Header
• Multiple Objects that share a common object
  header format
• Currently defined Objects
• MPLS Label Stack
• Extended Payload Bytes (payload bytes 129)

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TRACEROUTE An Additional Benefit
gt 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 Label100048 Exp0 TTL1 S1 3
10.1.24.2 (10.1.24.2) 0.822 ms 0.731 ms 0.708
ms MPLS Label100016 Exp0 TTL1 S1
4 10.100.6.1 (10.100.6.1) 0.961 ms 8.676 ms
0.875 ms
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Draft Status

• Introduced in 1999
• Deployed since 2001
• Updated draft version available at
• www.bonica.org/docs/draft-ietf-mpls-icmp-04.txt
• Resubmitted for your consideration