Viewing the World in Binary

OSPF/BGP – A few good things…


  • If router-id command not used under ‘ospf router’ definition

-> RI will be highest IP addr of a loopback interface. No loopback defined,  Then..

->  RI will be highest IP addr of first active interface.

  • Enabling OSPF on all interfaces

-> network area <number>


  • ebg-multihop option can only be used for eBGP and is not used for iBGP.
  • If ‘sh ip bgp summary’ shows state transitioning between Idle <-> Active. This is an indication of TCP issues between Peers.

BGP Load Balancing

  • Load Balancing in BGP – If the AS Path is different for route to same network, only one path will be installed in the routing table.  Load balancing will not take place.

EDGE1#sh ip route
Routing entry for
  Known via “bgp 60055”, distance 20, metric 0
  Tag 10055, type external
  Redistributing via ospf 1
  Last update from 00:37:40 ago
  Routing Descriptor Blocks:
  *, from, 00:37:40 ago
      Route metric is 0, traffic share count is 1
      AS Hops 2
      Route tag 10055

EDGE1#sh ip bgp
BGP routing table entry for, version 30
Paths: (2 available, best #2, table Default-IP-Routing-Table)
  Advertised to update-groups:
  20055 3000 from (
      Origin IGP, localpref 100, valid, external
  10055 3000 from (
      Origin IGP, localpref 100, valid, external, best

EDGE1#sh ip bgp

—- Output snipped —–

*                          0 20055 3000 i   <- Two different paths are present for route to network
*>                                  0 10055 3000 i



September 11, 2008 - Posted by | Protocols - OSPF |

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