Posted by: Richard @ Configureterminal.com | February 27, 2008

BGP Path Selection

A quick post about one of the key pieces of information that any potential CCIE has to know in-depth; how does BGP select a path?

I have put together a large but informative flow chart that details what happens:

BGP Path Selection - Small 

Click here to download a larger version of the image

I had come across this link on the internet but needed something with a bit more detail on it so I decided to ‘make my own’

The flow chart is based on information within Jeff Doyle’s ‘Routing TCP/IP, Volume 2’ and this link:

BGP Best Path Selection Algorithm 

Creating the document has really helped to etch the order in my mind J

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Responses

  1. BGP won’t consider any of the above unless the next-hop is considered reachable 🙂

  2. A valid point, I have made a presumption that the next hop is always available but I will amend the flow chart to represent your comment.

    Many thanks

  3. Very helpful, thanks!

    I’ve downloaded a copy to use for my SP exam.

  4. […] found this great link from Richard Bannister’s CCIE Blog. Richard has put together a great BGP Best Path Selection flow chart that details the order in which a path is chosen. Great […]

  5. Hi Richard,

    Just to inform you that chaeplin link is broken in the end of your article.

    Nice chart, well done!

  6. Hi Pello,

    Thanks for letting me know, luckily I had a copy saved locally on my laptop so I have uploaded it to https://rbcciequest.wordpress.com/files/2008/08/bgp_pathselection.jpg

    Nice OSPF MD5-Auth hack by the way.

    Thanks again 🙂

    Richard

  7. really a awesome post.

    regards
    shivlu jain

  8. Cool. Thank you very much, very useful. Added a reference in my blog to this post

  9. […] A nice chart illustrating the BGP bestpath selection process. […]

  10. excellent illustration of the best path algorithm.

    great post

  11. […] } Inspired by the  flow chart that Mr Richard Bannister did for the BGP route path selection, I did one for conventional route-selection in the […]

  12. Very useful indeed, 🙂

  13. […] The best post I have seen on the topic is this one that in detail illustrates the algorithm in a flow-chart: https://rbcciequest.wordpress.com/2008/02/27/bgp-path-selection/ […]

  14. […] This one courtesy of Richard Bannister’s CCIE Blog: […]

  15. hi richard very nice blog…

  16. […] والسلايد الثاني منقول من مدونة Richard Bannister’s CCIE Blog: […]

  17. […] https://rbcciequest.wordpress.com/2008/02/27/bgp-path-selection/ […]

  18. Quite interesting…

  19. […] found this great link from Richard Bannister’s CCIE Blog. Richard has put together a great BGP Best Path Selection flow chart that details the order in which a path is chosen. Great work! […]

  20. Anybody let me know to learn BGP for the scratch……

  21. Anybody let me know a good e-book to learn BGP from scratch????

    • For cisco routers, start with routing TCP/IP vol2 by cisco press.
      This will give you a very good start.


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