draft-ietf-mpls-self-ping-00.txt   draft-ietf-mpls-self-ping-01.txt 
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Expires: December 7, 2015 I. Minei Expires: December 7, 2015 I. Minei
Google, Inc. Google, Inc.
M. Conn M. Conn
D. Pacella D. Pacella
L. Tomotaki L. Tomotaki
M. Wygant M. Wygant
Verizon Verizon
June 5, 2015 June 5, 2015
LSP Self-Ping LSP Self-Ping
draft-ietf-mpls-self-ping-00 draft-ietf-mpls-self-ping-01
Abstract Abstract
When certain RSVP-TE optimizations are implemented, ingress LSRs can When certain RSVP-TE optimizations are implemented, ingress LSRs can
receive RSVP RESV messages before forwarding state has been installed receive RSVP RESV messages before forwarding state has been installed
on all downstream nodes. According to the RSVP-TE specification, the on all downstream nodes. According to the RSVP-TE specification, the
ingress LSR can forward traffic through an LSP as soon as it receives ingress LSR can forward traffic through an LSP as soon as it receives
a RESV message. However, if the ingress LSR forwards traffic through a RESV message. However, if the ingress LSR forwards traffic through
the LSP before forwarding state has been installed on all downstream the LSP before forwarding state has been installed on all downstream
nodes, traffic can be lost. nodes, traffic can be lost.
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that has been bound to the LSP most recently. Finally, the transit that has been bound to the LSP most recently. Finally, the transit
LSR sends the RESV message upstream, along the reverse path of the LSR sends the RESV message upstream, along the reverse path of the
LSP. LSP.
When the ingress LSR receives the RESV message, it installs When the ingress LSR receives the RESV message, it installs
forwarding state. Once the ingress LSR installs forwarding state it forwarding state. Once the ingress LSR installs forwarding state it
can forward traffic through the LSP. can forward traffic through the LSP.
Some implementations optimize the above-described procedure by Some implementations optimize the above-described procedure by
allowing LSRs to send RESV messages before installing forwarding allowing LSRs to send RESV messages before installing forwarding
state. This optimization is desirable, because it allows LSRs to state [RFC6383]. This optimization is desirable, because it allows
install forwarding state in parallel, thus accelerating the process LSRs to install forwarding state in parallel, thus accelerating the
of LSP signaling and setup. However, this optimization creates a process of LSP signaling and setup. However, this optimization
race condition. When the ingress LSR receives a RESV message, some creates a race condition. When the ingress LSR receives a RESV
downstream LSRs may not have installed forwarding state yet. If the message, some downstream LSRs may not have installed forwarding state
ingress LSR forwards traffic through the LSP before forwarding state yet. If the ingress LSR forwards traffic through the LSP before
has been installed on all downstream nodes, traffic can be lost. forwarding state has been installed on all downstream nodes, traffic
can be lost.
This memo describes LSP Self-ping. When an ingress LSR receives an This memo describes LSP Self-ping. When an ingress LSR receives an
RESV message, it can invoke LSP Self-ping procedures to verify that RESV message, it can invoke LSP Self-ping procedures to verify that
forwarding state has been installed on all downstream nodes. By forwarding state has been installed on all downstream nodes. By
verifying the installation of downstream forwarding state, the verifying the installation of downstream forwarding state, the
ingress LSR eliminates this particular cause of traffic loss. ingress LSR eliminates this particular cause of traffic loss.
LSP Self-ping is an extremely light-weight mechanism. It does not LSP Self-ping is an extremely light-weight mechanism. It does not
consume control plane resources on transit or egress LSRs. consume control plane resources on transit or egress LSRs.
Although LSP Ping and LSP Self-ping are named similarly, each is a Although LSP Ping and LSP Self-ping are named similarly, each is a
unique protocol. Each protocol listens on its own UDP port and unique protocol. Each protocol listens on its own UDP port and
executes is own unique procedures. executes is own unique procedures.
2. Applicability 2. Applicability
LSP Self-ping is applicable in the following scenario: LSP Self-ping is applicable in the following scenario:
o The ingress LSR signals a point-to-point LSP
o The ingress LSR receives a RESV message o The ingress LSR receives a RESV message
o The RESV message indicates that all downstream nodes have begun o The RESV message indicates that all downstream nodes have begun
the process of forwarding state installation the process of forwarding state installation
o The RESV message does not guarantee that all downstream nodes have o The RESV message does not guarantee that all downstream nodes have
completed the process of forwarding state installation completed the process of forwarding state installation
o The ingress LSR needs to confirm that all downstream nodes have o The ingress LSR needs to confirm that all downstream nodes have
completed the process for forwarding state installation completed the process for forwarding state installation
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o The need to conserve control plane resources on the egress LSR o The need to conserve control plane resources on the egress LSR
outweighs the need to determine whether downstream forwarding outweighs the need to determine whether downstream forwarding
state is correct state is correct
Unlike LSP Ping [RFC4379] and S-BFD [I-D.akiya-bfd-seamless-base], Unlike LSP Ping [RFC4379] and S-BFD [I-D.akiya-bfd-seamless-base],
LSP Self-ping is not a general purpose MPLS OAM mechanism. It cannot LSP Self-ping is not a general purpose MPLS OAM mechanism. It cannot
reliably determine whether downstream forwarding state is correct. reliably determine whether downstream forwarding state is correct.
For example, if a downstream LSR installs a forwarding state that For example, if a downstream LSR installs a forwarding state that
causes an LSP to terminate at the wrong node, LSP Self-ping will not causes an LSP to terminate at the wrong node, LSP Self-ping will not
detect an error. Furthermore, LSP Self-ping fails when either of the detect an error. In another example, if a downstream LSR erroneously
following conditions are true: forwards a packet without an MPLS label, LSP Self-ping will not
detect an error.
Furthermore, LSP Self-ping fails when either of the following
conditions are true:
o The LSP under test is signaled by the Label Distribution Protocol o The LSP under test is signaled by the Label Distribution Protocol
(LDP) Independent Mode [RFC5036] (LDP) Independent Mode [RFC5036]
o Reverse Path Forwarding (RPF) [RFC3704] filters are enabled on o Reverse Path Forwarding (RPF) [RFC3704] filters are enabled on
links that connect the ingress LSR to the egress LSR links that connect the ingress LSR to the egress LSR
While LSP Ping and S-BFD are general purpose OAM mechanisms, they are While LSP Ping and S-BFD are general purpose OAM mechanisms, they are
not applicable in the above described scenario because: not applicable in the above described scenario because:
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[I-D.akiya-bfd-seamless-base] [I-D.akiya-bfd-seamless-base]
Akiya, N., Pignataro, C., Ward, D., Bhatia, M., and J. Akiya, N., Pignataro, C., Ward, D., Bhatia, M., and J.
Networks, "Seamless Bidirectional Forwarding Detection Networks, "Seamless Bidirectional Forwarding Detection
(S-BFD)", draft-akiya-bfd-seamless-base-03 (work in (S-BFD)", draft-akiya-bfd-seamless-base-03 (work in
progress), April 2014. progress), April 2014.
[RFC4594] Babiarz, J., Chan, K., and F. Baker, "Configuration [RFC4594] Babiarz, J., Chan, K., and F. Baker, "Configuration
Guidelines for DiffServ Service Classes", RFC 4594, August Guidelines for DiffServ Service Classes", RFC 4594, August
2006. 2006.
[RFC6383] Shiomoto, K. and A. Farrel, "Advice on When It Is Safe to
Start Sending Data on Label Switched Paths Established
Using RSVP-TE", RFC 6383, September 2011.
Authors' Addresses Authors' Addresses
Ravi Torvi Ravi Torvi
Juniper Networks Juniper Networks
Email: rtorvi@juniper.net Email: rtorvi@juniper.net
Ron Bonica Ron Bonica
Juniper Networks Juniper Networks
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