I am experiencing a problem on the intranet of my institution. I am sitting in front of A and trying to connect to server B in another city.

My ssh sessions hang up quite often, especially when I have a lot of screen output or page up/down in $PAGER or change window in GNU screen. In ssh session, X11 forwarding is too slow to be used.

My vrdp sessions (with VBoxHeadless) also hang up a lot , usually when I drag a window around inside the remote guest OS.

I tried to use tcpdump to figure out why, and noticed that before the hang up, many packets with PSH flag from A is sent and after a while, many ACK packets from B all at once.

ping from A to B give a delay of 40ms, and traceroute gives 4 hops. wget gives the throughput to be on average ~50Mbps, but the speed is very unstable. All three routers along the way are with Cisco IOS 12.X (identified with nmap).

What seems to be the problem? How can I investigate more on such an issue? Any hints or ideas are appreciated.