Long BGP AS paths

Ken Chase math at sizone.org
Sat Sep 30 22:34:42 UTC 2017

The quagga thread I read specifically indicates that some (most?) versions don't
accept the {n,m} regexp repeat format. Thus the regexps as long as the
path you want to filter... :/

..or upgrade.


On Sat, Sep 30, 2017 at 06:29:36PM -0400, William Herrin said:
  >To the chucklehead who started announcing a 2200+ byte AS path yesterday
  >around 18:27 EDT, I beg of you: STOP. You've triggered a bug in Quagga
  >that's present in all versions released in the last decade. Your
  >announcement causes routers based on Quagga to send a malformed update to
  >their neighbors, collapsing the entire BGP session. Every 30 seconds or so.
  >For everyone else: please consider filtering BGP announcements with
  >stupidly long AS paths. There's no need nor excuse for them to be present
  >in the DFZ and you could have saved me a painful Saturday.
  >router bgp XXX
  > bgp maxas-limit 50
  >ip as-path access-list maxas-limit50 deny ^([{},0-9]+ ){50}
  >ip as-path access-list maxas-limit50 permit .*
  >Bill Herrin
  >William Herrin ................ herrin at dirtside.com  bill at herrin.us
  >Dirtside Systems ......... Web: <http://www.dirtside.com/>

Ken Chase - math at sizone.org Guelph Canada

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