SSH session hangs after user enters credentials
Article ID: CTX277639
Updated On:
Description
User is unable to ssh to a VPX from a device outside of the network where the netscaler resides. After authentication the putty session hangs with a blank screen. The ns.log shows a successful authentication event.
Resolution
To Fix this issue:
1. copy the sshd config file from etc "cp /etc/sshd_config /nsconfig/"
2. modify sshd_config file located in the nsconfig directory with the following: IPQoS=throughput (if throughput doesnt resolve your issue try IPQoS=reliability)
3. restart sshd or, reboot the netscaler.
Problem Cause
In OpenSSH version 8.1+ a DSCP value of AF21 is appended by default. This seems to break communication in some environments.
From OpenSSH manual:
* ssh(1)/sshd(8): the default IPQoS used by ssh/sshd has changed.
They will now use DSCP AF21 for interactive traffic and CS1 for
bulk. For a detailed rationale, please see the commit message:
https://cvsweb.openbsd.org/src/usr.bin/ssh/readconf.c#rev1.284
AF21 was selected as this is the highest priority within the low-latency
service class (and it is higher than what we have today). SSH is elastic
and time-sensitive data, where a user is waiting for a response via the
network in order to continue with a task at hand. As such, these flows
should be considered foreground traffic, with delays or drops to such
traffic directly impacting user-productivity.
