DoS, ICMP, proxies, SYNDefender

From: Tim Bass <>

   Tim, unfortunately ICMP UNREACHABLE can be sent some intermediate
router during routing flip process. For this reason some customer
prefer cut off this sort of ICMP - it would break running TCP connection.

Understood, however the conditions to terminate the connection
is not just as simple as UNREACHABLE. A few possible conditions:
(2) UNREACHABLE && TCP_SYN_STATE && sk->time_in_state

    I am not shure that it is in _ALL_ host types.
Experience gave me that some time I had problem with uninterraptable
service up to I configure router to cut off ICMP UNREACHABLE from

        - Leonid Yegoshin, LY22