"Louis A. Mamakos" wrote: > One possibility is that the code in icmp_input() processing the > PMTU discovery-induced ICMP message could verify that the returned > header in fact is associated with a connection on the host and > maybe even has sane sequence numbers (for TCP segments). This would > make it more difficult to just spray these packets at host and > drop the MTU on routes.
Of course, now you've let the dirty little secret out of the bag: the MTU is on the *route*, which means on the next hop, so a spoof that got through would frag basically all traffic out of the victim machine down to 296 bytes... A client machine could do much worse, of course, fragging the inverse traceroute until the fragging was successful, after sending the SYN, in response to the server's "SYN-ACK"... The obvious "fix" for that is to not let the MTU be dropped if the last sent packet's size is smaller than the drop-to (can't use a "max successful" because of multiple routes and/or route assymetry). This would prevent doing it on the "SYN-ACK", or other small packet (maybe disallowing it entirely, until the first data packet has been sent). But the obvious "fix" for the obvious "fix" is to establish a connection, and then trigger the largest packet you can to be sent from the server (e.g. request a big HTTP document, which most initial pages in fact are). It's always an arms race... -- Terry To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-hackers" in the body of the message
