HP MSR2000 Configuration Manual page 17

hops the packet has traversed in the MPLS network. The IP tracert facility can show the real path along
which the packet has traveled.
Figure 6 TTL propagation
When TTL propagation is disabled, the ingress node sets the label TTL to 255. Each LSR on the LSP
decreases the label TTL value by 1. The LSR that pops the label does not change the IP TTL value when
popping the label. Therefore, the MPLS backbone nodes are invisible to user networks, and the IP tracert
facility cannot show the real path in the MPLS network.
Figure 7 Without TTL propagation
Follow these guidelines when you configure TTL propagation:
HP recommends setting the same TTL processing mode on all LSRs of an LSP.
•
• To enable TTL propagation for a VPN, you must enable it on all PE devices in the VPN, so that you
can get the same traceroute result (hop count) from those PEs.
To enable TTL propagation:
Step
1. Enter system view.
Command
system-view
8
Remarks
N/A