This feature allows the separate configuration of TTL propagation for in transit and CPM generated IP packets, at the ingress LER within a VPRN service context. The following commands are supported:
config router ttl-propagate vprn-local [none | vc-only | all]
config router ttl-propagate vprn-transit [none | vc-only | all]
You can enable TTL propagation behavior separately as follows:
for locally generated packets by CPM (vprn-local)
for user and control packets in transit at the node (vprn-transit)
The following parameters can be specified:
The all parameter enables TTL propagation from the IP header into all labels in the stack, for VPN-IPv4 and VPN-IPv6 packets forwarded in the context of all VPRN services in the system.
The vc-only parameter reverts to the default behavior by which the IP TTL is propagated into the VC label but not to the transport labels in the stack. You can explicitly set the default behavior by configuring the vc-only value.
The none parameter disables the propagation of the IP TTL to all labels in the stack, including the VC label. This is needed for a transparent operation of UDP traceroute in VPRN inter-AS Option B such that the ingress and egress ASBR nodes are not traced.
This command does not use a no version.
The user can override the global configuration within each VPRN instance using the following commands:
config service vprn ttl-propagate local [inherit | none | vc-only | all]
config service vprn ttl-propagate transit [inherit | none | vc-only | all]
The default behavior for a VPRN instance is to inherit the global configuration for the same command. You can explicitly set the default behavior by configuring the inherit value.
This command does not have a no version.
The commands do not apply when the VPRN packet is forwarded over GRE transport tunnel.
If a packet is received in a VPRN context and a lookup is done in the Global Routing Table (GRT), (when leaking to GRT is enabled for example), the behavior of the TTL propagation is governed by the LSP shortcut configuration as follows:
when the matching route is an RSVP LSP shortcut:
configure router mpls shortcut-transit-ttl-propagate
when the matching route is an LDP LSP shortcut:
configure router ldp shortcut-transit-ttl-propagate
When the matching route is a RFC 3107 label route or a 6PE route, It is governed by the BGP label route configuration
When a packet is received on one VPRN instance and is redirected using Policy Based Routing (PBR) to be forwarded in another VPRN instance, the TTL propagation is governed by the configuration of the outgoing VPRN instance.
Packets that are forwarded in different contexts can use different TTL propagation over the same BGP tunnel, depending on the TTL configuration of each context. An example of this might be VPRN using a BGP tunnel and an IPv4 packet forwarded over a BGP label route of the same prefix as the tunnel.