Wednesday 2 April 2014

Centos iptables causing 'No route to host' message

This had me going for a while...

Two machines on the same subnet, client machine pings server machine fine, I can ssh from client to server, but when trying to connect to any other TCP service I get a 'No route to host' message!

I'm staring at the screen thinking "How can the TCP layer possibly have a bearing on routing at the IP layer below?.... that's bonkers". For a minute the long held belief that I had understood the core fundamentals of TCP/IP wavered. Thankfully I spotted a sentence on a blog stating that on some Linux distro's iptables erroneously reported 'No route to host' when dropping packets. Sure enough I checked my iptables rules and all ports were blocked except 22.... phew, sane again :-) 

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