On 10/Jun/16 19:34, Leo Bicknell wrote:
It does mean the provider creating the leak has already lost, but that doesn't mean it still isn't vital to protecting the larger internet. A good example of this is fire code. Most fire codes do not do much to prevent you from starting a fire in your own house/condo/apartment, but rather prevent it from spreading to your neighbors.
I've found communities to be robust at filtering very effectively. I have heard of software issues that may cause filters to stop working, but I have not yet encountered any such issues myself that had nothing to do with a mis-configuration or lack of understanding about how policies are evaluated by the router.
For instance, if you filter Customer A to A's Prefix list on ingress, B to B's, C to C's, it may also be prudent to filter outbound to your peers based on A+B+C's prefix list. When the ingress filter to A fails (typo, bug, bad engineer), your own network is hosed by whatever junk A ingested, but at least you won't pass it on to peers and spoil the rest of the Internet.
That does not scale, and was probably one of the primary reasons communities were developed.
Basically both ingress and egress filtering have weaknesses, and in some cases doing both can provide some mitigation. It's the old adage "belt and suspenders".
We've been operating purely community-based filtering on border and peering routers for years. I've never ran into an issue with the software that broke that. The folk I know who have suffered this either mis-configured their policies, did not understand BGP and did not get a good handle on how their router OS implements filtering and filter evaluation. Mark.