BGP--configuration help

Unanswered Question
Jun 28th, 2008

Hi Experts,

If I have a following scenario.What would be the best way to configure using BGP.


I have this problem too.
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sdoremus33 Sat, 06/28/2008 - 12:57

Yes some more info would be great but you could run ibgp between rtr's in AS100 and then run an EBGP link to AS200.HTH

amit.seth Sat, 06/28/2008 - 13:12

Let's say for example I have offices in two different cities.I have been allocated an AS number(100) for my organization.I have to connecect the two offices using BGP via an ISP

who is using AS 200.

How should I go about configuring my routers.Normally if an update from Office1 was to reach Office2 it would get discarded due to the repetition of the AS path Attribute.

devang_etcom Sat, 06/28/2008 - 19:57

Hi Amit,

you can use the "neighbor a.b.c.d allowas-in" on your both the office... that will allow to accept the update from same AS number in to your AS.


Devang Patel

Giuseppe Larosa Sun, 06/29/2008 - 03:16

Hello Amit,

I understand your concerns but the service provider can use some BGP commands so that you receive an AS path that doesn't contain your AS number.

I suppose your provider has given you an AS in the private range 64xxx - 65535.

So the isp can use commands like as-override this is tipically done in MPLS VPN context.

Otherwise you can use the BGP command allow-as in as told in another post

hope to help


waleed_amer Sun, 06/29/2008 - 04:25


the same AS number is used in CE1 & CE2 so they will not accept routes coming from the same AS number so you need to configure: neighbor x.x.x.x as-override into PEs ISP routers under address-family ipv4 vrf Customer1 so the PE will send bgp update with AS [200 200] instead of [200 100] and you can also use allow-as into CE router but by the two cases it is recommended to configure SOO if there a backdoor link or the site is connected to more than one PE router to avoid routing loops.



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