Brocade Multi-Service IronWare Administration Guide (Supporting R05.6.00) - Manual (Page 228)

210 Multi-Service IronWare Administration Guide
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LSP ping and traceroute
6
LSP ping and traceroute
Overview
The LSP Ping and Traceroute feature provides Operation, Administration, and Maintenance (OAM)
functionality for MPLS networks based up RFC 4379 (Detecting Multi-Protocol Label Switched
(MPLS) Data Plane Failures).
The LSP ping and traceroute functions provide a mechanism to detect MPLS data plane failure. LSP
ping is used to detect data plane failure and to check the consistency between the data plane and
the control plane. LSP traceroute is used to isolate the data plane failure to a particular router and
to provide LSP path tracing. They are implemented using MPLS echo request and reply messages
which are sent as UDP packets to a well-known UDP port 3503. This section provides the details of
LSP Ping and Traceroute operation
LSP ping operation
An MPLS echo request (described in “MPLS echo request” on page 210) is sent from the ingress to
the egress LSR. At the transit LSRs, the ping packet is label switched (the same as a regular MPLS
data packet) without any control plane intervention. Upon arriving at the egress LSR, the echo
request is sent to the control plane for processing based on the IP Router Alert option and the
well-known destination UDP port 3503. An echo reply (described in
“MPLS echo reply” on
page 211) is sent back as a UDP packet with an appropriate return code that depends on the result
of the FEC stack validation.
LSP traceroute operation
An MPLS echo request (described in “MPLS echo request” on page 210) is sent from the ingress
LSR with the TTL of the outermost label set to an incremental value that starts with a TTL value of
1. This request causes the MPLS echo request to be forwarded to the control plane for processing
at each transit LSR, based on the MPLS TTL expiration value. An echo reply (described in
“MPLS
echo reply” on page 211) is sent back with a return code indicating that it is the transit LSR for the
FEC specified in the echo request. This process repeats until the echo request arrives at the egress
LSP. The echo request is then forwarded to the control plane for processing, based on the IP Router
Alert option. An echo reply is sent back as a UDP packet with an appropriate return code that
depends on the result of the FEC stack validation.
MPLS echo request
The MPLS echo request is sent from the ingress LSR as a labeled UDP packet (except for single-hop
LSP). The echo request has the following characteristics.
IP/UDP header information:
• Source address = user-input or LSR ID.
• Destination address = user-input or 127.0.0.1.
• UDP source port = 3503.
• UDP destination port = 3503.
• IP TTL = 1