Route does not exist even though IP route looks fine
May 28
I'm trying to run SSH on a non-standard port. But I can't even get a TCP packet through.
IP routing works fine on port 22 and so does the actual connection:
downstream@localhost:~$ ip route get 172.234.232.12 ipproto tcp dport 22
172.234.232.12 via 172.234.224.1 dev eth0 src 172.234.224.188 uid 1000
cache
downstream@localhost:~$ nc -zvw2 172.234.232.12 22
Connection to 172.234.232.12 22 port [tcp/ssh] succeeded!
A route exists on port 2022 as well:
downstream@localhost:~$ ip route get 172.234.232.12 ipproto tcp dport 2022
172.234.232.12 via 172.234.224.1 dev eth0 src 172.234.224.188 uid 1000
cache
But when I ask to actually connect, the route is not there:
downstream@localhost:~$ nc -zvw2 172.234.232.12 2022
nc: connect to 172.234.232.12 port 2022 (tcp) failed: No route to host
linux1 answer
Accepted answer · original discussion
May 28
"No route to host" can also be the result of receiving an ICMP 'Destination Unreachable' – it is not exclusively local.
For example, it can be caused by a network firewall returning ICMP 'Destination Unreachable: Administratively Prohibited' when trying to connect to a blocked port. (And receiving the equivalent ICMPv6 message would even cause Linux to report "Permission denied".)
Use tcpdump -n icmp to see what is responding.
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