Passing multiple values using BGP

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May 9th, 2008
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I would like to know if it is posible to pass multiple values from one eBGP peer to another - i.e. with something similar to extended communities?

I.e. can an upstream peer pass 6 variables to the downstream peer for processing and making a route decision?

The only mechnism i can think of is extended communities and it's not possible to do it with this.


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Joseph W. Doherty Fri, 05/09/2008 - 04:15
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Would the BGP command set community {community-number [additive]}, using the additive option serve your need?

carl.forbes Fri, 05/09/2008 - 04:29
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Hmm, i don't think so. From what i understand of the additive option, it would appear to add an additional community in transit.

I would like to add e.g. 6 community variables at the same time and send them to the downsream peer.

Thanks for this though, I haven't come across 'additive' before but now i have more confidence that BGP can handle multiple community values - but how do you write them all at the same time?


Joseph W. Doherty Fri, 05/09/2008 - 05:00
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"but how do you write them all at the same time? "

Good question. Perhaps multiple set community additive commands within a route map, e.g. 6 in your case; unsure whether this is supported.

rais Fri, 05/09/2008 - 06:47
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So setting community multiple times in a route-map is not an option?

route-map rm permit 10

match ip address 10

set community 1:100

set community 1:101

set community 1:102


carl.forbes Fri, 05/09/2008 - 07:01
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I wasn't aware it was possible to do this, thanks, but leads me to another question. For the upstream peer receiving this update - is it possible to index each value individually. E.g.:

comm 1:100 = value [1]

comm 1:101 = value [2]

comm 1:102 = value [3]

So at the upstream, can i use syntax similar to reg exp within a route map and do: if value [2] = 101, route packet via int x?

Harold Ritter Fri, 05/09/2008 - 07:07
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You can do that as follow:

router bgp xx

neighbor x.x.x.x remote-as yyy

neighbor x.x.x.x route-map test out

neighbor x.x.x.x send-community


route-map test permit 10

set community 1:1 1:2 1:3 1:4 1:5 1:6




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