P2Mp Traceroute - Cisco CRS Configuration Manual

P2MP Traceroute

The MPLS echo request packet is sent to a target router through the use of the appropriate label stack associated
with the LSP to be validated. Use of the label stack causes the packet to be forwarded over the LSP itself.
The destination IP address of the MPLS echo request packet is different from the address used to select the
label stack. The destination IP address is defined as a 127.x.y.z/8 address. The 127.x.y.z/8 address prevents
the IP packet from being IP switched to its destination, if the LSP is broken.
An MPLS echo reply is sent in response to an MPLS echo request. The reply is sent as an IP packet and it is
forwarded using IP, MPLS, or a combination of both types of switching. The source address of the MPLS
echo reply packet is an address obtained from the router generating the echo reply. The destination address
is the source address of the router that originated the MPLS echo request packet.
The MPLS echo reply destination port is set to the echo request source port.
Only P2MP TE LSP IPv4 is supported. If the Responder Identifier TLV is missing, the echo request
Note
requests information from all responder-ids.
Jitter
Jitter is used to reduce the load on the LSR where the ping is performed. By adding a jitter, the replying routers
will space their reply time based on a random number between 0 and the jitter value, Jitter TLV, specified in
the packet.

P2MP Traceroute

The P2MP traceroute feature is used to isolate the failure point of a P2MP LSP. It is used for hop-by-hop fault
localization and path tracing. The traceroute feature relies on the expiration of the TTL of the packet that
carries the echo request. When the P2MP echo request message hits a transit node, it checks the TTL and if
it is expired, the packet is punted to the control plane, else the message is forwarded or replicated. If punted
to the control plane, a reply message is build based on the contents of the request message.
Traceroute can be applied to all nodes in the P2MP tree. However, you can select a specific traceroute target
through the P2MP Responder Identifier TLV. An entry in this TLV represents an responder-id or a transit
node. This is only the case for P2MP TE LSPs.
Only P2MP TE LSP IPv4 is supported. If the Responder Identifier TLV is missing, the echo request
Note
requests information from all responder-ids.
Jitter
Jitter is used to reduce the load on the LSR where the traceroute is performed. By adding a jitter, the replying
routers will space their reply time based on a random number between 0 and the jitter value, , Jitter TLV,
specified in the packet.
For more information about ping and traceroute commands, see MPLS OAM commands chapter in the
Cisco IOS XR MPLS Command Reference for the Cisco CRS Router.
Cisco IOS XR MPLS Configuration Guide for the Cisco CRS Router, Release 5.1.x
398
Implementing MPLS OAM