Specifying The Label Type Advertised By Egress; Configuring Ttl Propagation - HP FlexNetwork 10500 Series Configuration Manual

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If you do not configure the MPLS MTU of an interface, fragmentation for MPLS packets is based
on the IP MTU. If IP MTU is not configured, fragmentation for MPLS packets is based on the
MTU of the interface. The length of a fragment does not include that of the MPLS label. Thus,
after an MPLS label is added into a fragment, the length of the MPLS fragment might exceed
the interface MTU.

Specifying the label type advertised by egress

In an MPLS network, an egress node can advertise the following types of labels:
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Implicit null label with a value of 3.
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Explicit null label with a value of 0.
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Non-null label.
For LSPs established by a label distribution protocol, the label advertised by the egress node
determines how the penultimate hop processes a labeled packet.
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If the egress node advertises an implicit null label, the penultimate hop directly pops the top
label of a matching packet.
•
If the egress node advertises an explicit null label, the penultimate hop swaps the top label
value of a matching packet with the explicit null label.
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If the egress node advertises a non-null label, the penultimate hop swaps the top label of a
matching packet with the label assigned by the egress node.
Configuration guidelines
As a best practice, configure the egress node to advertise an implicit null label to the penultimate hop
if the penultimate hop supports PHP. If you want to simplify packet forwarding on egress but keep
labels to determine QoS policies, configure the egress node to advertise an explicit null label to the
penultimate hop. Use non-null labels only in particular scenarios. For example, when OAM is
configured on the egress node, the egress node 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 node.
For LDP LSPs, the mpls label advertise command triggers LDP to delete the LSPs established
before the command is executed and re-establishes 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 the label type
advertised by the egress
node 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
Command
system-view
mpls label advertise
{ explicit-null | implicit-null |
non-null }
8
Remarks
N/A
By default, an egress node
advertises an implicit null label to
the penultimate hop.