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Network based bgp community

Looking to setup a primary and secondary datacenters off a private mpls backbone. I was told that using bgp communities on the PE's and pushing it to the CE vrf's was the way to go. Anyone have a sample?

6 REPLIES
Purple

Re: Network based bgp community

I'm not sure I understand what you are trying to achieve here with communties. Could you provide a bit more detail ?

Paresh

Community Member

Re: Network based bgp community

Building a private MPLS backbone for a large area. This consists of 14 PE routers and no P routers. At two of the locations are datacenters for common services such as email, sap, etc. There is a common vpn assigned to all CE routers that includes the datacenters. In other words any to any. One datacenter will be primary and the other datacenter is for backup. OK so they are all on the same vrf.

I know I can do prepend path on the secondary datacenter CE which should inject an inferior path to it. But I was told that I should probably look at doing network based (PE) bgp communities. They are talking about injecting the appropriate routes to the CE's from the PE's. I am not that familiar with BGP community strings so was looking for a sample.

Re: Network based bgp community

Hello,

well reading about your project, this would be the time to get REALLY familar with BGP.

About communities: they are like markers or route tags. There is no meaning to them (besides some predefined ones for internet usage) unless you configure a route-map, which exactly describes, what you want to do with the prefixes carying a certain community.

Communities are for sure a way of setting up flexible IP address independant BGP policies. But they are not meant to replace policies.

So your first question would be: What do I want to achieve?

And then: does my policy require to identify a subset of all prefixes? If yes, then BGP communities might be a road to walk down.

An example of two BGP routers using communities:

RA:

router bgp 65000

neighbor 1.1.1.1 remote-as 65001

neighbor 1.1.1.1 send-community

neighbor 1.1.1.1 route-map SetComm out

ip bgp-community new-format

route-map SetComm permit 10

match ip address prefix-list 123

set community 65000:1

ip prefix-list 123 seq 5 permit 192.168.1.0/24

RB

router bgp 65001

neighbor 1.1.1.2 remote-as 65000

neighbor 1.1.1.2 send-community

neighbor 1.1.1.2 route-map SetStuff in

ip bgp-community new-format

route-map SetStuff permit 10

match ip community-list 123

set metric 4321

set local-preference 80

ip community-list 123 permit 65000:1

RA marks a special network and RB does some settings based on the existance of the community. The sexy thing about this is, that you can just change networks on RA without bothering RB (other AS).

Hope this helps! Please rate all posts.

Regards, Martin

Community Member

Re: Network based bgp community

Thanks got it.

Community Member

Re: Network based bgp community

Thanks got it.

Re: Network based bgp community

Hello,

well, reading about your project, this would be the time to get REALLY familar with BGP.

About communities: they are like markers or route tags. There is no meaning to them (besides some predefined ones for internet usage) unless you configure a route-map, which exactly describes, what you want to do with the prefixes carrying a certain community.

Communities are for sure a way of setting up flexible IP address independant BGP policies. But they are not meant to replace policies.

So your first question would be: What do I want to achieve?

And then: does my policy require to identify a subset of all prefixes? If yes, then BGP communities might be a road to walk down.

An example of two BGP routers using communities:

RA:

router bgp 65000

neighbor 1.1.1.1 remote-as 65001

neighbor 1.1.1.1 send-community

neighbor 1.1.1.1 route-map SetComm out

ip bgp-community new-format

route-map SetComm permit 10

match ip address prefix-list 123

set community 65000:1

ip prefix-list 123 seq 5 permit 192.168.1.0/24

RB

router bgp 65001

neighbor 1.1.1.2 remote-as 65000

neighbor 1.1.1.2 send-community

neighbor 1.1.1.2 route-map SetStuff in

ip bgp-community new-format

route-map SetStuff permit 10

match ip community-list 123

set metric 4321

set local-preference 80

ip community-list 123 permit 65000:1

RA marks a special network and RB does some settings based on the existance of the community. The sexy thing about this is, that you can just change networks on RA without bothering RB (other AS).

Hope this helps! Please rate all posts.

Regards, Martin

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