BGP Mulithoming

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Apr 22nd, 2009
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I have internet connectivity with 2 Internet service providers and i am doing BGP with them.I am using Cisco 3845 router for my internet connectivity so in BGP i just want to accept default route from the service provider and not the complete routing table.

i want to block the complete routing table from both the service i should proceed.Any sample config to block the same.

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Joseph W. Doherty Wed, 04/22/2009 - 03:18
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Besides filtering out received BGP routes to only accept a default, you might also discuss with your ISPs not sending the complete BGP route table and only sending the default.

sameermunj Wed, 04/22/2009 - 03:23
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I want to ensure the same from my end so wants the configuration details..

even if we confirm with isp about default route,some misconfiguration at there end at any point of time can make the 3845 router down.

please suggest the necessary configuration

Jon Marshall Wed, 04/22/2009 - 03:33
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Assuming the default-route provided by provider is then on your router(s)

access-list 1 permit

access-list 1 deny any

router bgp

neighbor distribute-list 1 in


Joseph W. Doherty Wed, 04/22/2009 - 03:39
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Didn't mean to infer you shouldn't filter out BGP routes, just made suggestion in case you hadn't considered it. What I had in mind was, why burn bandwidth passing the Internet BGP table if you don't want it.

If you're that concerned about ISP misconfigurations, and you never intend to use anything but the defualt, why BGP peer at all? Sure BGP can indicate a "dynamic" default, but if you don't trust your ISPs, you might want to use your own "dynamic" default.

As to suggesting a necessary configuration for your original question, don't believe it should be difficult, but I don't know it off the top-of-my-head. I'm sure another poster will provide it. (Again, just wanted to insure you've been considering other aspects.)



Ah, Jon provided the configure while I was typing the above.

sameermunj Wed, 04/22/2009 - 06:59
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The reason to use BGP peer is i have 2 diffrent isp's to whom i am announcing my own ip address pool.

The reason to get default route is the capacity of my 38xx router which i feel wont be able to take complete routing table.


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