North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical RE: On the back of other 'security' posts....
On Sat, 30 Aug 2003, Terry Baranski wrote: > > Sure, blocking spoofed traffic in the limited cases where it is feasible at > > the edge would be a good thing, but, I don't see failure to do so as > > negligent. > > In what instances is blocking spoofed traffic at the edge not feasible? > ("Spoofed" as in not sourced from one of the customer's netblocks.) Where the customer is not a basic end user.. an ISP for example who may be transiting traffic from netblocks that are not theirs. We still have the other problem where a lot of large networks are using RFC1918 addresses that do not get NAT'd thus filtering will break pMTU.. this is an issue in my experience mainly for those who host websites, altho many of those are filtering their own packets anyway and have broken sites! > > Where exactly do you think that the duty to care in this > > matter would come from for said ISP? > > Isn't the edge by far the easiest and most logical place to filter > spoofed packets? What are the good reasons not to do so? It is the only place, virtually any source and destination address could pass across our network core, there is no way to filter at any part of the Internet backbone > > Again, I just don't see where an ISP can or should be held liable for > > forwarding what appears to be a correctly formatted datagram with a valid > > destination address. > > I guess "correctly formatted" is a relative term. When *isn't* a packet > with a spoofed source IP address guaranteed to be illegitimate? Maybe > such packets shouldn't be considered "correct". Edge filtering ok. But in general it is not the job of the IP router to look into the higher level protocols to determine what the packet does. Look up papers on why this would be bad, RFC3439 by Randy and Dave Meyer is a good read! Steve
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