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CCNP question - BGP protocols

Posted on 2009-04-21
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Please answer to those questions, but don't send me to links... I would  like a simple explanation...

1) Routes learned by IBGP routers, are they propagated to other IBGP routers?
2) Routes learned by IBGP routers, are they propagated to other EBGP routers?
3) Routes learned by EBGP routers, are they propagated to other IBGP routers?
4) Why IGBP routers should be in a full mesh between each others withing the same AS?

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Question by:ping_it
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hau_it earned 2000 total points
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1. The answer is yes, as long as they are in a full mesh Maybe you dont see these routes in the routing table because you learn them with a better metric from an IGP protocol, but you can see them in the show ip bgp command

2. The answer is again yes. Every route has an origin and if you use the show ip bgp command then you will see in the last column where this route was originated

3. As long as the synchronization is off, the answer is yes. If you have the synchronization on then each IBGP router in order to add the EBGP route to the routing table and use it, he should know the route by an IGP. It was a common practice in old days to redistribute all the EBGP routes to the IGP protocols, but now with sync. off it is not needed

4. Because of the BGP split horizon rule, in order for loops to be avoided.  If they are not in full mesh then if an IBGP router learns a network he wont propagate it to the other.

Dimitris
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by:ping_it
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One more little thing about point number 3:

So if the synchronization is ON the IGBP router should know the EGBP route from an IGP router.

How can an IGP router know an external route that the IGBP doesn't know?

If I understand well the path is: IGP goes to IGBP and then to EGBP and vice versa, so when synchronization is on the EGBP routers exchange routes directly with IGP??
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by:ping_it
ID: 24198066
One more little thing about point number 3:

So if the synchronization is ON the IGBP router should know the EGBP route from an IGP router.

How can an IGP router know an external route that the IGBP doesn't know?

If I understand well the path is: IGP goes to IGBP and then to EGBP and vice versa, so when synchronization is on the EGBP routers exchange routes directly with IGP??
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by:hau_it
ID: 24201880
The sync. rule says that in order an IBGP neighbor to use and advertise to other IBGP neighbors a route the router must know that route through IGP. In some way all external routes should be redistributed to the IGP. Because this is CPU intensive the common practice now is to run full mesh INGP with the sync. off
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