Configuring Ttl Propagation - HP 10500 Series Configuration Manual

Configuration guidelines
If the penultimate hop supports PHP, HP recommends that you configure the egress to advertise an
implicit null label to the penultimate hop. If you want to simplify packet forwarding on the egress but keep
labels in packets for the egress to determine QoS policies, you can configure the egress to advertise an
explicit null label to the penultimate hop. HP recommends not using non-null labels except in some
special scenarios. For example, when OAM is configured on the egress, the egress can get the OAM
function entity status only through non-null labels.
As a penultimate hop, the device accepts the implicit null label, explicit null label, or normal label
advertised by the egress device.
The mpls label advertise command takes effect for the LDP LSPs and BGP LSPs established after the
command is executed. To apply the new setting to BGP LSPs established before the command is executed,
delete the routes corresponding to the BGP LSPs, and then redistribute the routes.
Configuration procedure
To specify the type of label that the egress node will advertise to the penultimate hop:
Step
1. Enter system view.
2. Specify the label type
advertised by the egress to the
penultimate hop.

Configuring TTL propagation

When TTL propagation is enabled, the ingress node copies the TTL value of an IP packet to the TTL field
of the label. Each LSR on the LSP decreases the label TTL value by 1. The LSR that pops the label copies
the remaining label TTL value back to the IP TTL of the packet, so the IP TTL value can reflect how many
hops the packet has traversed in the MPLS network. The IP tracert facility can show the real path along
which the packet has traveled.
Figure 12 TTL propagation
Command
system-view
mpls label advertise { explicit-null
| implicit-null | non-null }
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Remarks
N/A
By default, an egress advertises an
implicit null label to the penultimate
hop.