issue with no bgp default route-target filter

hi all, 

please tell me what is the exact mean of no bgp default ipv4 unicast and when it automatically disable or is this outomatically disable on RR.

and please also clearify me no bgp default route-target filter ???

why this automatically disable on ASBR RR??

in case there is no RR then what would be the function of this command?

actually when i need to transmit route from ASBR-P to ASBR-P with MP-eBGP relation then i have to manually disable bgp default route-target filter without manually assigning VRF on ASBR so why this happens?

but in Back-to-Back VRF, we dont need manually disable this command so what is the exact meaning of bgp default route-target filter??

one more thing -

what is the ralation of this command with next-hop feature actually how it works ??

Comments

  • The no bgp default ipv4 unicast command turns off sending of IPv4 NLRI unless we activate the address-family. Maybe we only want to send IPv6 NLRI or VPNv4 NLRI but not regular IPv4 NLRI, if we don't use this command we will receive the regular IPv4 prefixes as well.

    The no bgp default route-target filter is used on VPNv4 route reflectors. By default VPNv4 routes with RT that does not match local import of RT will not be installed in the routing table. This is the desired behaviour however  we don't want to define all VRFs on RR so we want to turn off this feature so that all routes will be installed even though RT is not matching import policy. It would be impossible for RR to reflect routes otherwise. 

    You talk about VRFs and P routers, maybe I am misunderstanding your English but VRFs should be defined on PE routers and VPNv4 routes should be announced to PE routers or RR. P routers should just switch packets based on label which is the IGP label announced by LDP.

  • thanks for this batter solution well actually it was wrongly written 

    it is really ASBR to ASBR with MP-eBGP well once again thanks i got it

  • It's not exactly correct.  For RR "no bgp default route-target filter" is irrelevant, it turns it off automatically.

    Mainly this command is used on ASBR for inter-AS VPN option B, which is not acting as RR inside its AS at the same time.

     

     

     

     

     

  • Hello ssfouzdar.ie,

    I am trying to answer you

    "please tell me what is the exact mean of no bgp default ipv4 unicast and when it automatically disable or is this outomatically disable on RR" question.

     

    By default ipv4-unicast enabled means when you configure:

    neighbor x.x.x.x remote-as <x>

    neighbor <x.x.x.x> update-source <xx> command it initiates the unicast BGP neighbor session (not vpnv4) by default.

    See here:

    R2#show running-config | section router bgp

    router bgp 1
     no synchronization
     bgp log-neighbor-changes
     neighbor 1.1.1.1 remote-as 1
     neighbor 1.1.1.1 update-source Loopback0
     no auto-summary
     !
     address-family vpnv4
      neighbor 1.1.1.1 activate
      neighbor 1.1.1.1 send-community extended
     exit-address-family

    R2#show ip bgp all summary
    For address family: IPv4 Unicast -- This is BGP ipv4 unicast session
    BGP router identifier 2.2.2.2, local AS number 1
    BGP table version is 1, main routing table version 1

    Neighbor        V    AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd
    1.1.1.1         4     1      12      12        1    0    0 00:04:06        0

    For address family: VPNv4 Unicast -- This is BGP VPNv4 unicast session
    BGP router identifier 2.2.2.2, local AS number 1
    BGP table version is 1, main routing table version 1

    Neighbor        V    AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd
    1.1.1.1         4     1      12      12        1    0    0 00:04:06        0
    R2#

    You noticed, there is vpnv4 and unicast BGP session with neighbor 1.1.1.1. If you want only vpnv4 BGP session rather than unicast use no bgp default ipv4-unicast command.

     

    See another example:

    R2#show running-config | section router bgp

    router bgp 1
     no synchronization
     bgp log-neighbor-changes

    no bgp default ipv4-unicast
     neighbor 1.1.1.1 remote-as 1
     neighbor 1.1.1.1 update-source Loopback0
     no auto-summary
     !
     address-family vpnv4
      neighbor 1.1.1.1 activate
      neighbor 1.1.1.1 send-community extended
     exit-address-family

    R2#show ip bgp all summary
    For address family: VPNv4 Unicast
    BGP router identifier 2.2.2.2, local AS number 1
    BGP table version is 1, main routing table version 1

    Neighbor        V    AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd
    1.1.1.1         4     1      23      23        0    0    0 00:00:18        0

    Now we have only VPNv4 BGP session.

    I don't think that it automatically disable on ASBR RR!!! Can you explain little bit more?

     

    If you have any more queries, welcome!!

    [:D]

  • i were discussing about bgp default route-target filter that this feature automaticaly disable or ASBR but this is right that this feature can be disabled on ASBR when it is not acting as RR in AS

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