Specifications

mpls ip ttl-expiration pop
MP-176
Cisco IOS Multiprotocol Label Switching Command Reference
January 2010
mpls ip ttl-expiration pop
To specify how a packet with an expired time-to-live (TTL) value is forwarded, use the mpls ip
ttl-expiration pop command in global configuration mode. To disable this function, use the no form of
this command.
mpls ip ttl-expiration pop l
abels
no mpls ip ttl-expiration pop l
abels
Syntax Description
Defaults The packets are forwarded by the original label stack. However, in previous versions of Cisco IOS
so
ftware, the packets were forwarded by the global routing table by default.
Command Modes Global configuration
Command History
Usage Guidelines You can specify that the packet be forwarded by the global IP routing table or by the packet’s original
la
bel stack. The forwarding method is determined by the number of labels in the packet. You specify the
number of labels as part of the command. If the packet contains the same or fewer labels than you
specified, it is forwarded through the use of the global IP routing table. If the packet contains more labels
than you specified, the packet is forwarded through the use of the original label stack.
This command is useful if expired TTL packets do not get back to their source, because there is a break
i
n the Interior Gateway Protocol (IGP) path. Currently, MPLS forwards the expired TTL packets by
reimposing the original label stack and forwarding the packet to the end of a label switched path (LSP).
(For provider edge routers forwarding traffic over a Virtual Private Network (VPN), this is the only way
to get the packet back to the source.) If there is a break in the IGP path to the end of the LSP, the packet
never reaches its source.
labels The maximum number of labels in the packet necessary for the packet to be
f
orwarded by means of the global IP routing table.
12.0S Packets are forwarded through the use of the global routing table.
12.0ST Packets are forwarded through the use of the original label stack.
12.1T Packets are forwarded through the use of the original label stack.
Release Modification
12.1(5)T This command was introduced.
12.2(33)SRA This command was integrated into Cisco IOS Release 12.2(33)SRA.
12.2SX This command is supported in the Cisco IOS Release 12.2SX train. Support
i
n a specific 12.2SX release of this train depends on your feature set,
platform, and platform hardware.