Alcatel-Lucent 6850-48 Guida Di Riferimento

BGP Commands

page 44-22

OmniSwitch CLI Reference Guide

Enables or disables synchronization of BGP prefixes with AS-internal routing information. Enabling this 
command will force the BGP speaker to advertise prefixes only if the prefixes are reachable through AS-
internal routing protocols (IGPs like RIP and OSPF). 

N/A

This command is disabled by default.

OmniSwitch 6850, 6855, 9000, 9000E

• Use the no form of this command to disable IGP synchronization.

• A BGP router is not supposed to advertise routes learned through internal BGP updates unless those 

routes are also known by the primary internal routing protocol (e.g, RIP or OSPF). However, requiring 
all routers in an AS to know all external routes places a heavy burden on routers focusing mainly on 
Intra-AS routing. Therefore, disabling synchronization avoids this extra burden on internal routers. As 
long as all BGP routers in an AS are fully meshed (each has a direct connection to all other BGP rout-
ers in the AS) then the problem of unknown external router should not be a problem and synchroniza-
tion can be disabled.

• By default, synchronization is disabled and the BGP speaker can advertise a route without waiting for 

the IGP to learn it. When the autonomous system is providing transit service, BGP should not propa-
gate IGP paths until the IGP prefixes themselves are known to be reachable through IGP. If BGP 
advertises such routes before the IGP routers have learned the path, they will drop the packets causing 
a blackhole.

• The BGP protocol must be disabled (using the 

command) before using this command. 

-> ip bgp synchronization

-> no ip bgp synchronization

Release 6.1; command was introduced.