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 | | Leave a comment

Going Green with Dynamips – FAQs

These are a few questions which came up while working on Dynamips, will add to the list as and when I hit a bump.

Q 1: How to save Dynamips configuration?

Step 1: Save the router configuration (yes “wr mem”).

Step 2: Under Dynagen Management Console

In your .net file “configuration” entry appears for all routers with saved configuration.

Next time when starting your .net topology make sure to enter ‘Y’ so as to retrieve the previously saved configuration information for the routers.

And if you are using GNS3 for configuring labs, make sure ‘Automatically clean the working directory’ under Edit -> Preferences -> Dynamips is unchecked.

September 11, 2008 Posted by | Dynamips | | Leave a comment

OSPF – Multi Area Lab


I will be publishing Dynampis file for the following Multi Area OSPF Implementation. More over will be referencing parts of the topology in various articles. Following Areas are implemented in this Design – Backbone / Frame Relay  / Totally Stubby  / Not So Stubby Area / EIGRP Area for Route Redistribution concepts.



September 4, 2008 Posted by | Protocols - OSPF | | Leave a comment