R3303-HP HSR6800 Routers MPLS Configuration Guide

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Figure 10 TTL processing when TTL propagation is enabled
• Disable TTL propagation—When an LSR labels a packet, it does not copy the TTL value of the
original IP packet to the TTL field of the label, and the label's TTL is set to 255. When an LSR pops
the stack-top label, it does not copy the label's TTL to the original packet, and if the LSR is the egress
LSR, it decreases the TTL value of the original packet by 1. Other LSRs do not change the TTL value
of the original packet. In this mode, the tracert result does not show the hops within the MPLS
backbone, as if the ingress and egress were connected directly.
Figure 11 TTL processing when TTL propagation is disabled
Configuration guidelines
HP recommends that you configure the same TTL processing mode on all LSRs along an LSP.
To enable IP 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. For more information about PEs, see
"Configuring MPLS L3VPN."
Configuration procedure
To configure TTL propagation of MPLS:
Ste
p
Command Remarks
1. Enter system view.
system-view N/A
2. Enter MPLS view.
mpls N/A