Netcom Outage (Was: My InfoWorld Column About NANOG)
avg at ncube.com
Wed Jun 26 09:51:43 UTC 1996
>> The IGP rerouting with modern link-state IGPs is sub-second
>> so the redundancy of interior paths is easy to achieve (perticularly
>> if you use tricks like BGP confederations which eliminate
>> need to recompute iBGP routing in case of IGP changes).
> Can you be more specific about this? How do you avoid
>the recompute and also avoid persistent routing loops after a
When BGP confederations are used, iBGP routes point to the exit
interface address in a satellite AS, instead of the border router's
address. That address is invariant (unlike the border router's,
which may change with changes in interior routing). This allows
to preserve BGP table unchanged in case of IGP changes, and simply
re-run one step of recursion (assembly of iBGP and IGP tables)
instead of sending costly BGP updates with new border router's
Of course, this works only if backbone is not fractured (i.e.
threre's still connectivity to all exits).
As for routing loops we all know whom to thank for the wise
decision to give packet forwarding higher priority than to
handling routing updates, and for using textual regexp matching
in policy evaluation, too.
More information about the NANOG