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Re: key change for TCP-MD5
- From: Iljitsch van Beijnum
- Date: Mon Jun 26 05:55:51 2006
On 26-jun-2006, at 2:06, Niels Bakker wrote:
The reason IPsec helps against a DoS against the CPU is that it
has an anti replay counter. IPsec implementations are supposed to
maintain a window, not unlike a TCP window, that allows them to
reject packets with an anti replay counter that's too far behind
or ahead of the last seen packets. So in order to make a packet
reach the CPU an attacker has to observe or guess an acceptable
value for the anti replay counter.
Actually, no. In a router you can easily filter away all IP
packets not destined to port 25 to a certain host (for, say, a mail
server). However, if those packets are IPsec encrypted, these TCP
headers are unavailable to routers in the path.
You can't have it both ways: either you encrypt the packet so that
nobody can look inside it, or you don't and people can.
But we weren't talking about encryption. Or about filtering packets
that go _through_ a router. What we were talking about was using the
IPsec authentication on BGP sessions and whether that's better than
using TCP with MD5 in relation to DoS attacks.