Since newer versions of Ubuntu like 20, you will find there is no longer dynagen and that the dynamips provided is faulty and will segfault each time:
Cisco Router Simulation Platform (version 0.2.14-amd64/Linux stable)
Copyright (c) 2005-2011 Christophe Fillot.
Build date: Apr 3 2018 12:20:29
Local UUID: 3c1c0b7f-2fab-4fda-b40b-74841d1bcfe0
Instance ID set to 1.
netio_tap_create: unable to open TAP device tap1 (No such fi........
A big problem over ssh and especially sshfs is that your connection will often timeout and disconnect after inactivity.
To fix this you can modify the server but it may not be practical or you may not have access. Why not send keep alives fom your end (client side)?
Just edit /etc/ssh/ssh_config (not to be confused with sshd_config as that is the server side):
Find the line that says "Host *" and change it like this:........