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  • 1.  Route reflector

    Posted 10-31-2015 05:29

    I have some doubt over some topoligies that i am seeing.

     

    there is a 2 bgp groups, and one is group having the cluster command, while another group doesnt have any cluster command. cluster : groupA, no cluster : groupB

     

    1. if the group that has the cluster command, groupA, does it means that it is a RR server, while the other group which doesnt have the cluster command, groupB will be the RR clients ?

     

    2. The RR cluster, have an ebgp peering, and the routes learned will be advertised to all the other ibgp peerings in groupB however, if the route that is being learned by clientA in groupB is advertised to the RR in groupA, the RR does not reflect the learned ebgp route by the clientA in groupB to another clientB in groupB

     

    is there a rule such that an ebgp learned route to an iBGP will not be advertised by the RR to another client in the iBGP group ?

     

     

     



  • 2.  RE: Route reflector
    Best Answer

    Posted 10-31-2015 10:09

    Hello,

     

    @virgiliohtc wrote:

    I have some doubt over some topoligies that i am seeing.

     

    there is a 2 bgp groups, and one is group having the cluster command, while another group doesnt have any cluster command. cluster : groupA, no cluster : groupB

     

    1. if the group that has the cluster command, groupA, does it means that it is a RR server, while the other group which doesnt have the cluster command, groupB will be the RR clients ?

     

     

     

    No. Peers in group B which  does not have "cluster" command, will be treated as regular iBGP peers.

     

    Reflection rules are documented in RFC 4456 section 5

    https://tools.ietf.org/html/rfc4456#page-5

     

    @virgiliohtc wrote:

     

    2. The RR cluster, have an ebgp peering, and the routes learned will be advertised to all the other ibgp peerings in groupB however, if the route that is being learned by clientA in groupB is advertised to the RR in groupA, the RR does not reflect the learned ebgp route by the clientA in groupB to another clientB in groupB

     

    is there a rule such that an ebgp learned route to an iBGP will not be advertised by the RR to another client in the iBGP group ?

     

     

     

    Your peers in group B are not RR clients if this group is configured WITHOUT "cluster".

    And yes, there is a rule for regular iBGP route propagation - regular iBGP peer never sends the route received from another iBGP peer to 3rd iBGP peer. Check out RFC 4271 section 9.2 https://www.ietf.org/rfc/rfc4271.txt :

     

    When a BGP speaker receives an UPDATE message from an internal peer,
   the receiving BGP speaker SHALL NOT re-distribute the routing
   information contained in that UPDATE message to other internal peers
   (unless the speaker acts as a BGP Route Reflector

    JUNOS implements per-group Route Reflection, so if You want to reflect to/from ALL iBGP peers then make sure they are all in the group(s) bearing the "cluster" command. You could use distinct "cluster" identifier per group.

     

    HTH

    Thanks

    Alex

     

     

     



  • 3.  RE: Route reflector

    Posted 11-02-2015 07:29

    Hi Alex

     

    Understood that abit better now.

    Thank you for your kind advice

     

     

     



  • 4.  RE: Route reflector

    Posted 11-11-2015 07:56

    Hello

     

    A short question, the router with the cluster configuration, have an ebgp peering with 2 different asn.

    the cluster will learn the route from asnA and then not readvertise the route learn from asnB.

    can i treat the ebgp peerings to the cluster as non-clients ?



  • 5.  RE: Route reflector

    Posted 11-11-2015 08:44

    Hello,

     

    @virgiliohtc wrote:

    Hello

     

    A short question, the router with the cluster configuration, have an ebgp peering with 2 different asn.

    the cluster will learn the route from asnA and then not readvertise the route learn from asnB.

     

    Is Your question "does this happen by default" ? The answer is "it depends".

    If ASN B is already in the AS_PATH of the route received from ASN A, then JUNOS router would not advertise it to ASN B.

    Otherwise it would happily advertise a route received from ASN A to ASN B if there is no policy prohibiting it from doing so.

     

     

    @virgiliohtc wrote:

     

    can i treat the ebgp peerings to the cluster as non-clients ?

    Not by default, You need to write a policy achieving this.

    HTH

    Thx

    Alex