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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: Defeating DoS Attacks Through Accountability
> Not so fast, there are situations when you are authorized to have a certain
> chunk of address space but elect not to advertise it a certain way for
> whatever reason. Maybe someone has a pipe that they want to use for
> outbound traffic only and they don't want to use it at all inbound traffic,
> and as a result, they don't advertise their routes across it. What
> justification do you use for dropping traffic that falls into this category?
It's a general principle.
Anyhow, they're going to get damned little inbound traffic unless they
announce a route for it to *someplace*. I think the original *general*
policy was "If we don't have ANY route for it, we don't accept the traffic",
which sort of makes sense - how would you get through a TCP 3-way handshake
if the SYN+ACK always got back a ICMP Host Unreachable? I saw no requirement
that the routing not be assymetric, only that routing exist.
I'm sure Mark Prior will correct me if I mis-read him... ;)
Actually since we use "ip verify unicast reverse-path" we expect the
route to come from the same place as the traffic.
Mark.
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