ssh command hang

[Ryan Rawdon]

> On Jan 7, 2020, at 3:30 PM, Bejiita78 . <tkhemili78 at gmail.com> wrote:
> 
> has anyone ever noticed that locally a system may respond just fine, but
> running a command like port make install or top would cause the ssh session
> to hang indefinitely?

This is a common sign of a MTU mismatch on a network segment somewhere between your client and the server (large segments/packets/frames go into a black hole and nobody knows); or the path has a properly-configured reduced MTU, but the server is sending the traffic with the Don’t Fragment bit set (IP header); but the device in the path dropping it due to a smaller MTU is not successfully having Packet Too Big ICMP errors get back to the server.  

If you perform a packet capture on the server, you will likely see it retransmitting one or more segments over and over - but not see those arriving to the client.  

The approach to diagnosing the point of the issue being introduced (MTU mismatch, ICMP filtering, or the server not utilizing ICMP PTB responses properly) depends largely on the network topology between your client and server; and your ability to investigate or reproduce the symptoms in systems along that path.

There are plenty of other potential causes for this behavior, but this is the first one I would investigate if experiencing this issue.  Have there been any network changes near your client or server that might have meddled with MTU sizes or ICMP blocking?