I am currently reading about Routing around Congestion Defense and the non feasibility of this approach. Since to use this method a lot of BGP poisoning would be necessary and to switch paths several times also a problem called "path hunting" comes into play I need to understand the update process and message propagation.

When I send out BGP Update messages that poison paths on selected ASes on the Network, how do these ASes further propagate the routing information, will they propagate them also to poisoned neighbors? How many hops will they be propagated (for poisoned/unpoisoned ASes)? Can I decide which way my BGP Update message takes and will all ASes read the message and also update their routing information on the path to my desired destination?

  • Tags are created as soon as you use them, as is explained on networkengineering.meta.stackexchange.com/questions/696/….
    – Teun Vink
    Nov 4, 2019 at 15:30
  • Since a certain reputation is necessary to create tags and I also already experienced in different sub-boards of stackexchange that sometimes mods will add tags when they consider a suggestion as relevant I thought I will add this suggestions at the end of the question.
    – baxbear
    Nov 4, 2019 at 15:51
  • 1
    I think the BGP tag is sufficient. Just my $0.02. Nov 5, 2019 at 3:27
  • alright then :)
    – baxbear
    Nov 5, 2019 at 12:45

1 Answer 1


You can read about the update process in RFC 4271, but here's a simple description:

  1. The router receives the UPDATE message from an established peer.
  2. Assuming it's valid, the router applies the inbound policy to filter/modify the update.
  3. The router recalculates the best path, and updates its routing table.
  4. The router sends updates to its peers, subject to any outbound policies.

So the updates travel from AS to AS. You have no control other than what updates your send to you neighboring ASes. All other ASes will update their tables according to their policies, which you have no control over (or probably even knowledge of).

  • Thank you very much for your answer this helped me alot. Only the link and also some other links seem not to work (maybe an issue of eduroam, don't know for sure) - this one does work: rfc-editor.org/rfc/rfc4271.txt
    – baxbear
    Nov 5, 2019 at 14:02
  • Back home now and the reachability of the linked resource seems to be indeed very likely to be a problem with eduroam. At least now I am able to access the resource.
    – baxbear
    Nov 5, 2019 at 17:18

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