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New Member

BGP multi exit routers

We have a configuration with 2x 7200 connected to a 6509. The 2 7200's have our transit and peering points. The 6500 is our core switch.

We are trying to get iBGP from the 7200's to the 6500 with some filtering for only the 7200 connected ASN and their connected ASN routes on the 7200s being replicated down.

We had full routes going to the 6500 but saw a major CPU spike and it started causing issues with voice and other traffic.

Here is the existing config..

6500--OSPF--7200-1--BGP/OSPF--7200-2

/ \ / \

/ \ / \

/ \ x \

/ \ / \

Telia Savvis XO client-ASN

We want to do the following..

6500

/ \

/ \

/ iBGP \

/ \

7200-1 7200-2

/ \ / \

/ \ / \

/ BGP \ / BGP \

/ \ / \

Telia Savvis XO client-ASN

I tried the following from the 7200's and the 6500.. I didn't receive any routes via iBGP on the 6500.

6500

ip as-path access-list 85 permit ^OUR-AS_[0-9]*$

ip as-path access-list 85 deny .*

router bgp OUR-AS

no synchronization

bgp router-id 1.2.182.254

no bgp log-neighbor-changes

neighbor 1.2.182.118 remote-as OUR-AS

neighbor 1.2.182.118 description iBGP to 7200-2

neighbor 1.2.182.118 filter-list 85 in

neighbor 1.2.176.2 remote-as OUR-AS

neighbor 1.2.176.2 description iBGP to 7200-1

neighbor 1.2.176.2 filter-list 85 in

************************************************************

7200-1

ip as-path access-list 80 permit ^OUR-AS_[0-9]*$

ip as-path access-list 80 deny .*

router bgp OUR-AS

no synchronization

no bgp log-neighbor-changes

neighbor 1.2.176.5 remote-as OUR-AS

neighbor 1.2.176.5 description iBGP to 6500

neighbor 1.2.176.5 default-originate

neighbor 1.2.176.5 filter-list 80 out

************************************************************

7200-2

ip as-path access-list 80 permit ^OUR-AS_[0-9]*$

ip as-path access-list 80 deny .*

router bgp OUR-AS

no synchronization

no bgp log-neighbor-changes

neighbor 1.2.176.2 remote-as OUR-AS

neighbor 1.2.176.2 description iBGP to 6500

neighbor 1.2.176.2 filter-list 80 out

1 ACCEPTED SOLUTION

Accepted Solutions

Re: BGP multi exit routers

Hi,

Sorry missed the $ ,ie permit ^AS1_[0-9]*$

regards

vanesh k

6 REPLIES
New Member

Re: BGP multi exit routers

See attached.. the text based version above didn't quite work out as planned

Re: BGP multi exit routers

Hi,

Pls note that , you are importing the routes to your 6500 via ibgp and it would not carry your AS path attached to the bgp updates .

So you need to modify the filter , allowing your peer AS and his connected customer

just do this change , instead of " your As " , give your peering AS one by one

like permit ^AS1_[0-9]*

permit ^AS2_[0-9]*

and last a deny as given by your

Hope this helps

regards

vanesh k

Re: BGP multi exit routers

Hi,

Sorry missed the $ ,ie permit ^AS1_[0-9]*$

regards

vanesh k

New Member

Re: BGP multi exit routers

Thanks...

I thought it was a bit over filtered ;-) That did hte trick.. now on to moving an L2 connection so the 7200-2 can talk directly with the 6500..

Here are the results using all me peering and transit ASN info..

6500#sh ip bgp sum

BGP router identifier 1.2.182.254, local AS number OUR_AS

BGP table version is 24923, main routing table version 24923

24822 network entries and 24822 paths using 3301326 bytes of memory

1439 BGP path attribute entries using 86520 bytes of memory

1055 BGP AS-PATH entries using 25320 bytes of memory

0 BGP route-map cache entries using 0 bytes of memory

1442 BGP filter-list cache entries using 17304 bytes of memory

BGP activity 24855/1386 prefixes, 24871/49 paths, scan interval 60 secs

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd

1.2.176.2 4 OUR_AS 70034 17 24923 0 0 00:13:24 24822

New Member

Re: BGP multi exit routers

My only remaining problem is I also want to have a full mesh for iBGP between both 7200's in addition to the 6500. Everytime I bring up iBGP between the 7200's I have looping.

Just need to work that part out and I will be a happy camper. Any suggestions?

Re: BGP multi exit routers

Hi ,

You can have a full mesh of ibgp between both the 7200 and 6500 router and there would not be any loop as a ibgp learned route would not be given to another ibgp neighbor

But make sure that , you have filters with your upstream provider bgp such that only your prefixes are advertised via bgp to them .The reason is that once you bring up the ibgp between both 7200 router , you act like a transit between the ISP's .If you have necessary filters in your Out with Ebgp neighbors , you donot have any problem.

Pls rate posts if helpful

regards

vanesh k

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