Brocade Multi-Service IronWare Administration Guide (Supporting R05.6.00) - Manual (Page 232)

214 Multi-Service IronWare Administration Guide
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LSP ping and traceroute
6
PHP behavior
Ping is transparent to the penultimate LSR. MPLS and IP TTL operations performed on a ping
packet are the same as tor a regular data packet. In the default case where the MPLS TTL is copied
into the IP TTL, the echo request packet can arrive at the egress LSR with an IP TTL value greater
than 1. Consequently, in this situation, the IP Router Alert option is used to direct the echo request
packet to the control plane for ping processing.
For a traceroute operation; if the echo request is received with a downstream mapping TLV, the
Implicit Null label is encoded in the Downstream label in the echo reply just like any other label.
Since a Brocade device advertises an implicit Null label to its upstream LSR for both LDP and RSVP
LSPs, packets that arrive at the egress LSR do not have the tunnel label. For a single-hop LSP, the
echo request is sent out from ingress LSR as an unlabeled UDP packet.
Using the LSP ping and Traceroute commands
The following sections described operation of the LSP Ping and Traceroute command:
• “Executing LDP LSP ping”
• “Executing RSVP LSP ping”
• “Executing LDP LSP traceroute”
• “Executing RSVP LSP traceroute”