R0106-HP MSR Router Series MPLS Command Reference(V7)

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Usage guidelines
The mpls ttl expiration enable command enables an LSR to generate an ICMP TTL-expired message upon
receiving an MPLS packet with TTL being 1.
• If the MPLS packet has only one label, the LSR sends the ICMP TTL-expired message back to the
source through IP routing.
• If the MPLS packet has multiple labels, the LSR forwards the ICMP TTL-expired message along the
LSP of the MPLS packet to the egress, which then sends the message back to the source.
Examples
# Disable the MPLS TTL-expired messages sending function.
<Sysname> system-view
[Sysname] undo mpls ttl expiration enable
mpls ttl propagate
Use mpls ttl propagate to enable TTL propagation.
Use undo mpls ttl propagate to disable TTL propagation.
Syntax
mpls ttl propagate { public | vpn }
undo mpls ttl propagate { public | vpn }
Default
TTL propagation is enabled for public network packets and disabled for VPN packets.
Views
System view
Predefined user roles
network-admin
Parameters
public: Specifies public network packets.
vpn: Specifies VPN packets.
Usage guidelines
When TTL propagation is enabled, MPLS does the following:
• Copies the IP TTL to the label TTL for packets entering the MPLS network.
• Copies the label TTL to the IP TTL for packets leaving the MPLS network.
If you enable TTL propagation on both the ingress and egress, the IP tracert facility can show the real
path in the MPLS network.
When TTL propagation is disabled, MPLS does the following:
• Sets the label TTL to 255 for packets entering the MPLS network.
• Pops the label for packets leaving the MPLS network, without copying the label TTL value to the IP
TTL.
The IP tracert facility cannot show the real path in the MPLS network.