Juniper BGP, Configuration Manual

Page: 252 / 748

exposed header's TTL is either left unchanged (when the forwarded option for the
mpls ip propagate-ttl command has been configured) or is decremented by 1 from
the incoming TTL value. If MPLS needs to push more labels, it sets the TTL for each
label according to the following LER rules, because for those labels the router
effectively is an ingress LER.
Rules for Processing on an LER
On an LER, when the packet is a locally originated IP packet, MPLS copies the TTL
of all pushed MPLS labels from the IP header when the
local option for the mpls ip
propagate-ttl command has been configured. When the no mpls ip propagate-ttl
local command has been configured, MPLS sets the TTL to 255.
When the packet is a forwarded IP or MPLS packet, MPLS copies the TTL of all pushed
labels from the inner IP or MPLS header when the
forwarded option for the mpls ip
propagate-ttl command has been configured. When the no mpls ip propagate-ttl
forwarded command has been configured, MPLS sets the TTL for these pushed labels
to 255.
When the packet is neither IP nor MPLS, such as a Martini packet, MPLS sets the TTL
of all pushed labels to 255.
216 ■
MPLS Label Switching and Packet Forwarding
JUNOSe 11.1.x BGP and MPLS Configuration Guide