Uses of BGP Communities

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Jun 2nd, 2009
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Well we do not use BGP communities here at work but I'm getting to know them for my BSCI exam.


1. Why are there separate well-known communities for no-export and local-AS? They both seem designed to do the same thing.


2. What's the use of non-well-known communities? It seems like they'd accomplish the same thing as route tagging.


Thanks.


Correct Answer by Edison Ortiz about 7 years 12 months ago

Hi,


Local-AS will not advertise to other ASes within the confederation while No-Export will.


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Edison.

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Edison Ortiz Tue, 06/02/2009 - 12:21
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1. Not the same thing.


No-Export:

Routes with this community are advertised to only peers in the same autonomous system or to only other subautonomous systems within a confederation. These routes are not advertised to external peers.


Local-AS:

Routes with community are advertised to only peers that are part of the local autonomous system or to only peers within a subautonomous system of a confederation. These routes are not advertised external peers or to other subautonomous systems within a confederation.


2. Yes, it's tagging of routes.


HTH,


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Edison.

CriscoSystems Tue, 06/02/2009 - 13:01
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"No-Export:

Routes with this community are advertised to only peers in the same autonomous system or to only other subautonomous systems within a confederation. These routes are not advertised to external peers.


Local-AS:

Routes with community are advertised to only peers that are part of the local autonomous system or to only peers within a subautonomous system of a confederation. These routes are not advertised external peers or to other subautonomous systems within a confederation."


The difference then is....?

Correct Answer
Edison Ortiz Tue, 06/02/2009 - 13:08
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Hi,


Local-AS will not advertise to other ASes within the confederation while No-Export will.


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CriscoSystems Tue, 06/02/2009 - 13:09
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You mean other confederations within the AS?

Edison Ortiz Tue, 06/02/2009 - 13:15
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A confederation is a group of sub-ASes, so the correct term is 'ASes within a confederation'.


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CriscoSystems Tue, 06/02/2009 - 13:27
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Hmmm, and here I thought a confederation WAS a sub-AS.


BGP is not for tiny networks.


Thanks for the xplanation.


mirzaakberali Tue, 06/02/2009 - 22:50
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Hello Edison,


Your above Post and Link extremely useful.


~Mirza.

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