There are pathological (aka: stupid) cases of multihomed to 2 isps,
getting static-routing of each isp's PA space on only that one ISP...
and default routing up both pipes... but really that's just broken and
dumb, so getting customers to fix this by filtering is a fine answer.
As I said in the original message, calling the customers stupid is not
useful.
They know they're doing asymmetrical routing, and they're paying the ISP a
lot of money to do so.
Regards,
John Levine, johnl(_at_)taugh(_dot_)com, Taughannock Networks, Trumansburg NY
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