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Contributor
cyke
Posts: 56
Registered: ‎06-02-2008
0

question on bgp community name

Hi,

 

I have 3 routers (RouterA, RouterB and RouterC) connected as A---B---C.   RouterB and RouterC are route reflectors.  I want routes learned by RouterB from RouterA advertised to RouterC but I don't want RouterC to readvertise these routes to other peers.  Can this restriction be configured from RouterB only?

 

I'm looking at bgp community names (no-advertise), no sure though if this is the right solution.

 

a sample config of the policy-statement would be great.  Thanks in advance

 

 

Recognized Expert
mhariry
Posts: 339
Registered: ‎06-01-2011
0

Re: question on bgp community name

Hi,

 

It is by default on BGP in your case you have two RR which is B & C so when B receive BGP update from client (A) it advertise it to C but C detect that the update has same cluster-id so it reject the update.

 

That's why it is recommended when you have more than one RR in your domain you have to build BGP peer which all your client for all BGP RR

 

Regards,

Mohamed

Regards,
Mohamed Elhariry
2* JNCIE (SEC # 159, SP # 1059),JNCIP-ENT

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Trusted Contributor
acecanal
Posts: 149
Registered: ‎07-05-2011

Re: question on bgp community name

[ Edited ]

 

 

 Hi Cyke, look at the following configuration example. This will set a self configured community called Net172, but as Mhariry said you have to use the well known community no-advertise. Well know community are standard values that have a pre defined behaviour, no-advertise ---- >dont advertise to other peers, no-export ---> dont advertise outside local AS.

 

  Or you could configure your own community and use a policy that will block its advertisement only to some peers.

 

 

policy-statement Net172 {
    term Net172Conn {
        from {
            prefix-list Net172;
        }
        then {

            metric 172172;


            community add Net172;   <---- Add community to prefix attributes, you could also replace current communities or delete some.

            as-path-prepend "172 16 100";
            accept;
        }
    }
    from {
        prefix-list Net10;
    }
    then accept;
}

 

 

 

 /* This is my own community configuration. */
community Net172 members 172:172;

 

 


bgp {
    local-address 10.1.1.1;
    export CONN-RI1;

    group RI2 {

        type external;   <------------- In your case will be type internal.


        local-address 10.1.1.1;

 

        export Net172;    <----------------- apply here under the group configuration.

 

        neighbor 10.2.2.2 {
            metric-out 172;
            multihop {
                ttl 2;
            }
            peer-as 65502;
        }
    }
}

Br
Alex

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