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Context
config>router>interface
Description
This command enables synchronization of IGP and LDP. When a link is restored after a failure, IGP
sets the link cost to infinity and advertises it. The actual value advertised in OSPF is 0xFFFF (65535).
The actual value advertised in IS-IS regular metric is 0x3F (63) and in IS-IS wide-metric is
0xFFFFFE (16777214). This feature is not supported on RIP interfaces.
Note that if an interface belongs to both IS-IS and OSPF, a physical failure will cause both IGPs to
advertise infinite metric and to follow the IGP-LDP synchronization procedures. If only one IGP
bounced on this interface or on the system, then only the affected IGP advertises the infinite metric
and follow the IGP-LDP synchronization procedures.
Next LDP hello adjacency is brought up with the neighbour. The LDP synchronization timer is started
by IGP from the time the LDP session to the neighbor is UP over the interface. This is to allow time
for the label-FEC bindings to be exchanged.
When the LDP synchronization timer expires, the link cost is restored and is re-advertised. IGP will
announce a new best next-hop and LDP will use it if the label binding for the neighbor's FEC is
available.
If the user changes the cost of an interface, the new value is advertised at the next flooding of link
attributes by IGP. However, if the LDP synchronization timer is still running, the new cost value will
only be advertised after the timer expired. Also, the new cost value will be advertised after the user
executes any of the following commands if the currently advertised cost is different:
If the user changes the value of the LDP synchronization timer parameter, the new value will take
effect at the next synchronization event. In other words, if the timer is still running, it will continue
using the previous value.
If parallel links exist to the same neighbor, then the bindings and services should remain UP as long
as there is one interface that is UP. However, the user configured LDP synchronization timer still
applies on the failed then restored interface. In this case, the router will only consider this interface
for forwarding after IGP re-advertized its actual cost value.
Note that the LDP Sync Timer State is not always synched across to the standby CPM, so after an
activity switch the timer state might not be same as it was on the previous active CPM.
The no form of this command disables IGP/LDP synchronization and deletes the configuration
Default
no ldp-sync-timer
Parameters
seconds — Specifies the time interval for the IGP-LDP synchronization timer in seconds.
loopback
Syntax
[no] loopback
7750 SR OS Router Configuration Guide
•
tools>perform>router>isis>ldp-sync-exit
•
tools>perform>router>ospf>ldp-sync-exit
•
config>router>interface>no ldp-sync-timer
•
config>router>ospf>disable-ldp-sync
•
router>isis>disable-ldp-sync
Values
1 – 1800
IP Router Configuration
Page 159
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