Re: 'set community' command ...

Answered Question
Nov 24th, 2008
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Hi,

Just want to know more abt. the usage of this command. I know the command has its attributes like ie) export, internet ...etc. I want to know that if I see something like this,


set community 65111:2211


Is this command used to tag routes so that when it reached its neighbor, further action can be taken on it ?


Pls advice,


Cheers,

- InternetB -

Correct Answer by royalblues about 8 years 6 months ago

Yes exactly.


Communities are used to tag certain routes so that appropriate action can be taken on the prefixes carrying this tag as per the defined policy.


There are 4 standard communities available


internet

By default all prefixes belong to this community


no-export

routes tagged with this community are not advertised to any external BGP peers


no-advertise

Routes tagged with this community are not advertised to any BGP peer (external as well as internal)


Local-as

It is similar to no-export community but within a confederation


http://www.cisco.com/web/about/ac123/ac147/archived_issues/ipj_6-2/bgp_communities.html


HTH

Narayan

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Correct Answer
royalblues Mon, 11/24/2008 - 03:19
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Yes exactly.


Communities are used to tag certain routes so that appropriate action can be taken on the prefixes carrying this tag as per the defined policy.


There are 4 standard communities available


internet

By default all prefixes belong to this community


no-export

routes tagged with this community are not advertised to any external BGP peers


no-advertise

Routes tagged with this community are not advertised to any BGP peer (external as well as internal)


Local-as

It is similar to no-export community but within a confederation


http://www.cisco.com/web/about/ac123/ac147/archived_issues/ipj_6-2/bgp_communities.html


HTH

Narayan

Joseph W. Doherty Mon, 11/24/2008 - 04:29
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"Is this command used to tag routes so that when it reached its neighbor, further action can be taken on it ?"


Another, yes.


Actions taken are up to the policies between the two neighbors (and even further downstream neighbors, including perhaps different ASs). Most common usage is providing some selection or preference for choosing a path.


You also have the option of sending more than one community per route.

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