Line vty 0 4 missing from configuration

[ckk_indy]

Apologies in advance if this is in the wrong board.  I didn't see a better place to put it.

I have a Catalyst 9200 (IOS-XE Gibraltar 16.12) that periodically refuses all Telnet/SSH connections.  After a seemingly random amount of time I can sometimes connect again.  I did a packet capture and see that a TCP RST comes back from the switch after I send a SYN.  Console access has always worked and when I get in that way to try and troubleshoot this I see that "line vty 0 4" is missing completely from the configuration.  I have never seen this before,  I've attempted to manually enter the lines back in, but they don't show up in the config.  Could this be the problem, and how might I go about fixing it?  So far, I have tried:

Manually adding the line vty 0-4 lines back in.  The switch seems to accept the commands but then they don't show up under a show run.

Zeroizing and re-creating the rsa keys (various lengths)

Enabling telnet and http server just to see if something will connect.

Reverting back to SSHv1 from SSHv2

Using local credentials

Any help would be appreciated!

[MHM Cisco World]

Show line,

See if line still online.

To solve this issue use 

Tcp keepalive in sw, this make sw down line if other peer not reply to keepalive message.

[marce1000]

 - You may have a few options : 1) Save config to external device - factory reset (or equivalent action for  9200) , restore config , check if problems persists 2) Use/upgrade latest advisory release in combination with item one  (e.g.)  https://software.cisco.com/download/home/286320176/type/282046477/release/Amsterdam-17.3.4b , 3) Can be executed on items one or two  too  = have a cold power cycle , look for self-test errors during cold startup 4) Check the logs when  you try to put the vty's back in (show logging). Look for errors - if any

 M.

[balaji.bandi]

can you post below output :

#show run | in vty

#show run all | in vty

[ckk_indy]

Thanks for the reply.  I will try and get that for you the next time I can get into it (if I have to console in I will have to drive.  It's at another site).

[Georg Pauwen]

Hello,

also check if there are any hung TCP sessions, using the exec command:

show tcp tcb

and if there are any entries, clear these lines using the command:'

clear tcp tcb #