(Optional) Configuring the MPLS TTL Processing Mode
Context
MPLS processes the TTL in the following modes:
MPLS TTL processing modes
In MPLS VPN applications, the MPLS backbone network needs to be shielded to ensure network security. The MPLS Pipe mode on the ingress node is recommended for private network packets. To reflect the path where packets pass, use the MPLS Uniform mode on the ingress node.
Path where ICMP response packets are transmitted
By default, when the received MPLS packet contains only one label, the LSR directly sends an ICMP response packet to the sender using an IP route. When the received MPLS packet contains multiple labels, the LSR sends an ICMP response packet to the sender along an LSP.
The MPLS VPN packets may contain only one label when they arrive at an autonomous system boundary router (ASBR) on the MPLS VPN, or a superstratum PE (SPE) device in HoVPN networking. These devices have no IP routes to the sender, so they forward the ICMP response packets along an LSP.
The MPLS VPN packets may contain only one label when they arrive at an autonomous system boundary router (ASBR) on the MPLS VPN. These devices have no IP routes to the sender, so they forward the ICMP response packets along an LSP.
Procedure
- Configuring the MPLS TTL processing mode
Perform the following steps on the ingress node.
- Run undo ttl propagate
The MPLS TTL processing mode is set to Pipe.
Or run ttl propagate
The MPLS TTL processing mode is set to Uniform.
By default, the TTL propagate function is enabled and the MPLS TTL processing mode is Uniform.
The ttl propagate command only take effect on LSPs that are to be set up. Before using the function on LSPs that have been set up, run the reset mpls ldp command to reestablish the LSPs.
- Run undo ttl propagate
- Configuring the path where ICMP response packets are transmitted
Perform the following steps on the ingress and egress nodes.