7 ms·
Uh, you know you can scan UDP ports just fine, right? Hosts reply with an ICMP destination unreachable / port unreachable (3/3 in IPv4, 1/4 in IPv6) if the por
by eqvinox 10mo ago
Uh, you know you can scan UDP ports just fine, right? Hosts reply with an ICMP destination unreachable / port unreachable (3/3 in IPv4, 1/4 in IPv6) if the port is closed. Discarding packets won't send that ICMP error.
It's slow to scan due to ICMP ratelimiting, but you can parallelize.
(Sure, you can disable / firewall drop that ICMP error… but then you can do the same thing with TCP RSTs.)
- apstls 10mo agoThat's why you discard ICMP errors.
- eqvinox 9mo agoIf anything, that's why you discard ICMP port unreachable, which I assume you meant. If you're blanket dropping all ICMP errors, you're breaking PMTUD. There's a special place reserved in hell for that. (And if you're firewalling your ICMP, why aren't you firewalling TCP?)