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 is 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 performs the following operations:

• 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 ingress and egress, the IP tracert facility can show the real path in the MPLS network.

When TTL propagation is disabled, MPLS performs the following operations:

• 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.

Within an MPLS network, TTL is always copied between the labels of an MPLS packet. The mpls ttl propagate command affects only the propagation between IP TTL and label TTL.

As a best practice, set 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. This allows you to obtain the same traceroute result (hop count) from those PEs.

Examples

# Enable TTL propagation for VPN packets.

<Sysname> system-view
[Sysname] mpls ttl propagate vpn