BGP Route selection problem

Hi

 

Can somebody explain this (for me this is a bug):

=============================================================

rtr1#sh ip bgp 12.12.12.12
BGP routing table entry for 12.12.12.12/32, version 17
Paths: (2 available, best #1, table Default-IP-Routing-Table)
Flag: 0x608
  Advertised to non peer-group peers:
  10.0.1.10
  (65000 65002), (received & used)
    10.0.1.10 from 10.0.1.10 (10.0.10.100)
      Origin IGP, metric 0, localpref 100, valid, confed-external, best
  (65002), (received & used)
    10.0.12.12 from 10.0.12.12 (10.0.12.12)
      Origin IGP, metric 0, localpref 100, valid, confed-external

=============================================================

 

For me there is a problem: the route with longuest AS Path is chosen

 

Thanks for any help

 

Best regards

 

Comments

  •  

     

    This is correct :the first one is the best.


     

    by default ,if "the AS-PATHs are  all in ( ....)"-------, the AS-PATHs length = 0;

    (btw :by default ,when  "the AS-PATHs are  all in ( ....)" ,the MED is not taken into account too;

            except you enable "bgp bestpath med-confed")

     

     

    both local-pre = 100;

    both AS-PATHs length = 0 (because there are no ASs outside "(....)";

    both med = 0;

    both "IBGP" --(confed-external = "IBGP" in bgp best path selection)

    both to the next-hop (10.0.1.10  and 10.0.12.12) is equal ( connected  yes?)

    the rules 10 : "the oldest prefix is better  " is only for  "EBGP"  (confed-external = "IBGP" in bgp best path selection)

    so the best path seection goes to rules 11 :

    ----so  compare   the router-id  :10.0.10.100 < 10.0.12.12

     

    so the first prefix is good.

     

    You can find the cisco documents "bgp best path selection" to confirm it, this is not bug,

    its a correct consequence.

     

     

     

     

     

     

     

    rtr1#sh ip bgp 12.12.12.12
    BGP routing table entry for
    12.12.12.12/32, version 17
    Paths: (2 available, best #1, table
    Default-IP-Routing-Table)
    Flag: 0x608
      Advertised to non
    peer-group peers:
      10.0.1.10
      (65000 65002), (received &
    used)
        10.0.1.10 from 10.0.1.10 (10.0.10.100)
          Origin
    IGP, metric 0, localpref 100, valid, confed-external, best
     
    (65002), (received & used)
        10.0.12.12 from 10.0.12.12
    (10.0.12.12)
          Origin IGP, metric 0, localpref 100, valid,
    confed-external

Sign In or Register to comment.