Bad routing update into the global routing table. Especially by a Tier1 transit isp. If at&t starts flooding with a lot if /32 (or /24 even) or makes itself the

Bad routing update into the global routing table. Especially by a Tier1 transit isp. If at&t starts flooding with a lot if /32 (or /24 even) or makes itself the shortest AS path hop to a lot of ASes or important ASes it would be bad. Even with rpki and all that, ISPs that don't participate can cause a cascading failure. Just knocking out verisign's root server routes for example.