Community Tags between eBGP AS

[heavy3122]

Hello,

I would like to know how long a route would maintain its community tag when it traverses ASs?

Basically, a route is tagged 100:1000 when exiting AS100, and then accepted into AS200. AS200 will not modify the tag. Would AS200 export the route to AS300 with the same 100:1000 tag?

Thanks

[Reza Sharifi]

Hi,

Yes, the router just passes the community attribute without modifying it from one router to another.

Here is doc with examples:

http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a00801475b2.shtml

HTH

[Giuseppe Larosa]

Hello heavy3122,

the BGP community attribute can be propagated without any change or additional BGP communities can be added to the route.

Multiple BGP communities are supported and usually new BGP communities are added.

However, it is technically possible to remove a BGP community when desired, but this case is less common.

You can check if the route still has the desired BGP community using a looking glass.

See

http://www.traceroute.org

for a list of looking glasses

In this way you can understand what changes, if any, have been performed by your upstream provider

Hope to help

Giuseppe

[Miroslav Berkov]

You can see how the BGP communities works on public route servers using basic show commands on CLI