BGP and No Synchronization

[oneciscokid]

I've created simple lab environment and lets say you have two routers in the same AS, so it's using iBGP. The first router (routerA) has a loopback interface assigned such as 10.1.1.0/24 to mimick an internal network. When you use the network command to have the network advertised the second router doesn't receive it and only receives it if No Synchronization is applied on it. I've read some documentation on No synchronization but don't fully understand it if it's just two routers in the same AS.

TIA

 

[oneciscokid]

I mean, the second router receives the advertised route but it doesn't add it to it's routing table.

 

[octavian10]

Synchronization is intended for situations in which your AS acts as a transit for packets from one AS to another, but where some of the routers in your AS do not run BGP. In this case the routers that only run the IGP need to have the same routing table as the BGP routers, or the AS could become a black hole for the unsynchronized routes. If synchronization is enabled in your situation BGP will only advertise routes that are present in both the IGP and BGP route tables. Once again in your situation you do not need to cary the routing table through the IGP so there for syncronization needs to be diabled. After reading this back to my self I do not think I did a good job of explaining syncronization, but hopefully it helps.
Have a good one.

"I hear and I forget. I see and I remember. I do and I understand."
- Confucius (551 BC - 479)

 

[plshlpme]

with synchronization enabled... while Router B doesn't have a route to the 10.1.1.0/24 network in its igp it will not add it to the bgp table..

if you ran an igp (ospf, eigrp etc) and it contained that network then bgp would add it to the table.

 

[jneiberger]

If synchronization is turned on, BGP will not place a route into the BGP table unless it already exists in your routing table. It is safe--even recommended--to turn this off unless you really need it. A properly designed topology usually doesn't require it.