Specifying The Label Type Advertised By The Egress; Configuring Ttl Propagation - HP MSR2000 Configuration Manual

Specifying the label type advertised by the egress

In an MPLS network, an egress can advertise the following types of labels:
Implicit null label with a value of 3.
•
Explicit null label with a value of 0.
•
Non-null label.
•
For LSPs established by a label distribution protocol, the label advertised by the egress determines how
the penultimate hop processes a labeled packet.
If the egress advertises an implicit null label, the penultimate hop directly pops the top label of a
•
matching packet.
If the egress advertises an explicit null label, the penultimate hop swaps the top label value of a
•
matching packet with the explicit null label.
• If the egress advertises a non-null label (normal label), the penultimate hop swaps the top label of
a matching packet with the specific label assigned by the egress.
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 to determine QoS policies, configure the egress to advertise an explicit null label to the
penultimate hop. HP recommends using non-null labels only in particular 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.
For LDP LSPs, the mpls label advertise command triggers LDP to delete the LSPs established before the
command is executed and reestablishes new LSPs.
For BGP LSPs, the mpls label advertise command takes effect only on the 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
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
Command
system-view
the label type
mpls label advertise { explicit-null
| implicit-null | non-null }
7
Remarks
N/A
By default, an egress advertises an
implicit null label to the penultimate
hop.