IBGP SYNCHRONIZATION

[stephtchoko]

I want to implement ibgp connection between 3 router, accross a IGP router, i would like to kwnow if i have to redistribute BGP into IGP ?

[Harold Ritter]

It is imperative not to redistribute BGP into the IGP if you carry the full internet routing table in BGP.

Synchronization is most likely disable by default in most of the recent IOS releases. Syncronization would only be required if your AS acts as a transit AS and if some of your internal routers in your AS do not run BGP.

Hope this helps,

[stephtchoko]

thank,

normally the BGP use tcp 179 to communicate with its neighbor.IBGP is implemented, across IGP router. how the IGP will know about routing information between the 2 IGP router ?

I will take an example:

there is my topology

RTA--RTB--RTC

|

RTD--------ISP

RTA and RTD are both IBGP router (RTA have to advertise network 194.202.251.0 to RTD)

RTB and RTC are both IGP router.

How the router RTB and RTC will route traffic to network 194.202.251.0 ???

Best regards.

[stephtchoko]

There is the topotlogy example.Normally RTD is connected to RTC and ISP

RTA--RTB--RTC--RTD-----ISP

Escume me.

Regards.

[Harold Ritter]

It would normally be recommended to run BGP on RTB and RTC as well. This way all routers would know about the routes coming from outside your AS from BGP.

Hope this helps,

[stephtchoko]

In the case that RTB, RTC can't run routing protocol can we try IBGP in RTA and RTD ?

In the case, use of transit AS with IBGP with synchronization, how the transit AS route the network exchange between the IBGP router ?

Best regards.

[Harold Ritter]

Even if you run iBGP between RTA and RTD, you would still need to either run BGP on RTB and RTB (fully meshed with RTA and RTD) or to redistribute BGP in the IGP on RTA and RTD. The latter is not recommended nor possible if you have lots of BGP routes since it would most certainly overwhelmed your IGP.

In the case you run iBGP between RTA and RTD, you need and IGP for the two routers to get basic IP connectivity. Static would work too but is not very practical.

Hope this helps,

[stephtchoko]

thank You.

Please can you send me a case study example for AS transit with ibgp (or ebgp).

Best regards.

[Harold Ritter]

In a transit network both iBGP and eBGP are required. eBGP to external peers and iBGP to internal ones.

Here's a case study that covers many different aspects of BGP.

http://www.cisco.com/univercd/cc/td/doc/cisintwk/ics/icsbgp4.htm

Hope this helps,