Command or Action Purpose
Step 6 exit
Example:
Router(config)# exit
Exits global configuration mode and enters privileged EXEC mode.
Step 7 show mpls ldp discovery [all | detail |vrf vpn-
name]
Example:
Router# show mpls ldp discovery
Displays the LDP identifier for the local router.
Example
The following example assigns interface pos2/0/0 as the LDP router ID:
Router> enable
Router# configure terminal
Router(config)# mpls ip
Router(config)# mpls label protocol ldp
Router(config)#
mpls ldp router-id pos2/0/0 force
The following example displays the LDP router ID (10.15.15.15):
Router# show mpls ldp discovery
Local LDP Identifier:
10.15.15.15:0
Discovery Sources:
Interfaces:
Ethernet4 (ldp): xmit/recv
LDP Id: 10.14.14.14:0
Preserving QoS Settings with MPLS LDP Explicit NullNormally, LDP advertises an Implicit Null label for directly connected routes. The Implicit Null label
causes the second last (penultimate) label switched router (LSR) to remove the MPLS header from the
packet. In this case, the penultimate LSR and the last LSR do not have access to the quality of service
(QoS) values that the packet carried before the MPLS header was removed. To preserve the QoS values,
you can configure the LSR to advertise an explicit NULL label (a label value of zero). The LSR at the
penultimate hop forwards MPLS packets with a NULL label instead of forwarding IP packets.
Note An explicit NULL label is not needed when the penultimate hop receives MPLS packets with a label stack
that contains at least two labels and penultimate hop popping is performed. In that case, the inner label can
still carry the QoS value needed by the penultimate and edge LSR to implement their QoS policy.
When you issue the mpls ldp explicit-null command, Explicit Null is advertised in place of Implicit Null
for directly connected prefixes.
Preserving QoS Settings with MPLS LDP Explicit Null
How to Configure MPLS LDP
MPLS LDP Configuration Guide, Cisco IOS Release 12.4
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