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bgp community in Juniper (will it pass it to others by defualt)

  • 1.  bgp community in Juniper (will it pass it to others by defualt)

    Posted 01-15-2018 08:13

    Just want to confirm.

    We know that bgp communities are Optional transitive, which means if my upstream router does not have this community configured or does not even understand communuty it should pass it to all its neighbours.

     

    Scenario:

              isp      isp

    R1---->R2--->R3---->R4 . (all ebgp or ibgp, should not matter)

     

    If I tag some routes with community on R1 and send it to  upstream router R2, even though R2 might be unaware of this community ( do not create this community) or does not understand them it should pass it to R3, and finally I can match routes on R4 based on community I configured  on R1

     

     Cisco routers should use "neighbor 3.3.3.3 send-community" command in order to be able to pass communities to other routers. Otherwise router will receive route with update but will advertise without it. 

     

    What is default behaviour on Juniper routers? will they by default pass communties to other routers unless I configure policy to remove the communties?

     

    Thanks, 

     

     

     



  • 2.  RE: bgp community in Juniper (will it pass it to others by defualt)

    Posted 01-15-2018 08:41

    Yes, JUNOS will advertise the route as it is to the other neighbors.

    You will need to explicitly define a policy to delete the community.

    HTH



  • 3.  RE: bgp community in Juniper (will it pass it to others by defualt)

    Posted 01-15-2018 13:53

    Hello,


    elsanov@amazon.com wrote:

    Just want to confirm.

    We know that bgp communities are Optional transitive,

       


    This is 100% true only for non-extended communities.

    BGP Extended Communities can be either transitive or non-transitive.

    https://www.iana.org/assignments/bgp-extended-communities/bgp-extended-communities.xhtml

     


    elsanov@amazon.com wrote:

     

    What is default behaviour on Juniper routers? will they by default pass communties to other routers unless I configure policy to remove the communties?

     

    Thanks, 

     


    No JUNOS configuration is required to accept any BGP communities (extended or non-extended, transitive or non-transitive) and then pass it to (ei)BGP peers , except as mentoned below.

    Explicit JUNOS configuration is required to strip transitive BGP communities (extended or non-extended) before passing them to (ei)BGP. peers. 

    Regarding non-transitive extended communities: except special-case extended communities like EVPN/origin validation/flowspec (which most people don't normally see or use), JUNOS supports only 1 non-transitive extended BGP community called "link bandwidth", and it is stripped by default across AS boundary.

    HTH

    Thx

    Alex 



  • 4.  RE: bgp community in Juniper (will it pass it to others by defualt)

    Posted 01-30-2018 02:20

    Optional transitive communities are always forwarded by default in Junos.