Archive for May, 2010

Influencing Inbound vs. Outbound Traffic flow in BGP

There are multiple ways of influencing Inbound vs. Outbound Traffic flow in BGP. The most common ones are:

Inbound Traffic Flow can be influenced by manipulating the following attributes –>

  • AS-Path Prepending
  • MED

Outbound Traffic Flow can be influenced by manipulating the following attributes –>

  • Weight
  • Local Preference

No Comments

BGP Route Selection Order!!!

Yes, I am still ALIVE. Sorry folks for not being able to post stuff on a more consistent basis. I have been extremely busy lately. However I don’t like excuses… so time to get to WORK 🙂

Here are the most common BGP route selection path attributes that are taken into consideration when a BGP speaking router has multiple routes in its BGP routing table & it has to make a decision which route to mark as best & put in its routing table. Here is the exact order:

  1. Prefer highest Weight
  2. Prefer highest Local Preference
  3. Prefer routes that the router originated (with the Network or Redistribute command)
  4. Prefer shortest AS-Path
  5. Prefer lowest origin code (i<?)
  6. Prefer lowest MED (metric)

Please note that there are more path attributes than the ones listed above. But the ones mentioned in this post are the most important path attributes used most frequently. For a complete list please visit the following link: BGP Best Path Selection Algorithm

No Comments