Lots of prepends - AS20912 case

Giuliano Peritore g.peritore at panservice.it
Fri Feb 20 05:15:38 CST 2009


         The long (176) AS20912 prepend incident was due to a 
misconfiguration of a BGP router we were testing.

         The problem is that differently to Cisco the syntax of the 
prepend field on thius system is not a string (eg. "20912 20912 
20912") but an integer, that the user interface _should_ limit to the 
interval 0-16.

         Unfortunately something has gone wrong with the syntax 
checker so you can enter a number (the number entered, thinking to 
Cisco syntax, was 20912) and the sotware interpreted it as the 
request of 20912 prepends... (0x51B0), dropped the highest 8 bits and 
processed it as the request of 0xB0=176 prepends.

         The producer has been warned about the problem, which I 
can't completely define as a "bug"... but the lack of a user 
configuration helper (syntax checker).

         I think that the case of AS47868 is the same, because I seed 
the modulo was involved too.

         Many thanks to one of our upstream providers for their support.


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         Giuliano Peritore - g.peritore at panservice.it
         Direzione Generale - Panservice
         Servizi professionali per Internet ed il Networking
         Panservice e' associata AIIP -- RIPE Local Registry
         Phone: +39 0773 410020 Fax +39 0773 470219
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