08-22-2012 10:39 PM - edited 03-04-2019 05:20 PM
All,
I am looking at some guidance on implementing route preference using BGP communities in our WAN network. Our service provider provided MPLS network spans the entire globe. I spoke to our service provider on influencing default route selection based on regions. For example countries in AsiaPac should prefer Singapore and stuff like that.
Our service provider came back to me and said that this can be implemented as he has made the community attribute to be transparent throught the network. My question is even if he has done that how do I proceed. Does anyone have some links/docs on communities implementation?
Regards,
Nik
08-23-2012 03:44 AM
Nik,
Communities are somewhat arbitrary numbers, with the exception of 4 standard communities (no-export, no-advertise, internet, local-as), and they're used for routing decisions. If the provider has assigned you a community to send to them, let's use 555:100 for example, they are expecting you to send this community with your routes. You can do this with a route-map applied to the neighbor:
route-map Community permit 10
set community 555:100
router bgp 1
neighbor 1.1.1.1 route-map Community out
neighbor 1.1.1.1 send-community
The above would set 555:100 on all of your routes. If you needed to set a community for a subset of routes, you'd change the route-map to match on a prefix list and then set the community that way:
ip prefix-list Singapore permit 192.168.1.0/24
ip prefix-list Brazil permit 192.168.2.0/24
ip prefix-list US permit 192.168.3.0/24
route-map Community permit 10
match ip address prefix Singapore
set community 100:200
route-map Community permit 20
match ip address prefix Brazil
set community 200:200
route-map Community permit 30
match ip address prefix US
set community 300:200
and the BGP configuration is the same. The provider on the other side would be looking for any routes that have these communities attached and they'd make routing decisions based on them.
Here's a document on named communities:
http://www.cisco.com/en/US/docs/ios/12_2t/12_2t8/feature/guide/ftbgpncl.html
HTH,
John
** Please rate useful posts ***
08-23-2012 04:30 AM
Hi, the service provider has not assigned any communities to me. He has just said he has set the communities to be transparent in his network.
08-23-2012 04:45 AM
Okay, their telling you that they're not going to strip them from your routes. That would mean that you would need to match on your communities on the other side and then make routing decisions based on whatever community you were matching on.
John
08-23-2012 10:16 AM
Disclaimer
The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.
Liability Disclaimer
In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.
Posting
I dealt with a similar situation several years ago. Used community values to define a "virtual" AS topology, i.e. each site would tag its outbound routes with a community denoting it's virtual AS. On received routes, examined received community and prepended original AS by virtual AS hops.
08-23-2012 11:13 AM
Nik
Perhaps there is some aspect of your situation and your question that I do not understand correctly. But it seems to me that you have a fairly simple issue and I do not see where communities are needed.
If I am understanding correctly you have multiple remote sites. Each remote site has a Customer Edge Router (CE) which connects to the Provider Edge Router (PE). The PE will advertise a default route to the CE. The CE will use the default route to send its outbound traffic to its connected PE. Once the traffic is in the provider clould you no longer are making choices about how it will be forwarded.
So where would communities enter into this? If I have misunderstood something then please clarify.
HTH
Rick
Find answers to your questions by entering keywords or phrases in the Search bar above. New here? Use these resources to familiarize yourself with the community: