Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.os.linux.networking > #4674

Re: Delay when SSH'ing into some systems in my LAN

Show all headers | View raw

On 2020-07-21, S.K.R. de Jong <SKRdJ@nowhere.net> wrote:
> 	This started happening recently, with no apparent reason.
>
> 	I have systems A, B, C, D in my LAN. When I SSH from A into B the 
> connection gets established immediately. However when I do it from A to C 
> I get the following SSH traces in A:
>
> 	OpenSSH_7.4p1, OpenSSL 1.0.2u  20 Dec 2019
> 	debug1: Reading configuration data /home/xyz/.ssh/config
> 	debug1: Reading configuration data /etc/ssh/ssh_config
> 	debug2: resolving "C" port 22

Try to ssh into C using C's IP address rather than name. 
If that goes immediately
Try putting C's name into A's /etc/hosts
Since it seems to be A that is complaining, try putting C's name and
address into /etc/hosts on A. 
It seem's that it is the reverse dns that is problematic.
Note that in the above A,B,C,D could be names or they could be IP
addresses. It might help to actually give us the exact log lines, rather
than the edited ones.


>
> It hangs at that point for 20 seconds or so, but then the connection 
> succeeds. Once it is established, the performance of the session is as 
> expected. The same behavior is observed when I try to SSH from A into D.
>
> 	Taking the "resolving "C" port 22" as a clue, I thought that I 
> might be having DNS problems in A. That does not seem to be the case 
> though:
>
> 	$ dig C
>
> 	; <<>> DiG 9.11.19 <<>> mimir
> 	;; global options: +cmd
> 	;; Got answer:
> 	;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 63806
> 	;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, 
> ADDITIONAL: 1
>
> 	;; OPT PSEUDOSECTION:
> 	; EDNS: version: 0, flags:; udp: 4096
> 	;; QUESTION SECTION:
> 	;C.				IN	A
>
> 	;; ANSWER SECTION:
> 	C.			0	IN	A	192.168.0.9
>
> 	;; Query time: 0 msec
> 	;; SERVER: 192.168.0.7#53(192.168.0.7)
> 	;; WHEN: Tue Jul 21 09:07:02 MDT 2020
> 	;; MSG SIZE  rcvd: 50
>
> The resolution happens with no delay, but the SSH connection attempt to C 
> keeps taking 20 seconds, as above. And analogously for D.
>
> 	Now once I have SSH'd into C, I can SSH from C into D with no 
> delay. I can even SSH from C into A (or B, or D) with no delay 
> whatsoever. In general, if A is not involved as a client things seem to 
> be normal.
>
> 	So it would seem that the problem is in A alone, and not when 
> trying to SSH into every system - only some seem to be affected.
>
> 	Any suggestions on how to diagnose this? I can't see anything 
> relevant in the logs of the systems involved - the only thing present is 
> the delay I mentioned, in the circumstances that I described. In A I have 
> the following IPtables rules:
>
> 	Chain INPUT (policy ACCEPT)
> 	target     prot opt source               destination         
>
> 	Chain FORWARD (policy DROP)
> 	target     prot opt source               destination         
> 	ACCEPT     all  --  0.0.0.0/0            0.0.0.0/0            	
> state RELATED,ESTABLISHED
> 	ACCEPT     all  --  0.0.0.0/0            0.0.0.0/0           
>
> 	Chain OUTPUT (policy ACCEPT)
> 	target     prot opt source               destination         
>
> whereas in the other systems I have no IPtables rules. I stopped and 
> starting the network in A, to no avail. I guess that rebooting A might 
> solve the problem. Or not. Even if it does, I would not understand why.

Back to comp.os.linux.networking | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Delay when SSH'ing into some systems in my LAN "S.K.R. de Jong" <SKRdJ@nowhere.net> - 2020-07-21 15:27 +0000
  Re: Delay when SSH'ing into some systems in my LAN William Unruh <unruh@invalid.ca> - 2020-07-21 16:28 +0000
    Re: Delay when SSH'ing into some systems in my LAN "S.K.R. de Jong" <SKRdJ@nowhere.net> - 2020-07-21 18:29 +0000
      Re: Delay when SSH'ing into some systems in my LAN William Unruh <unruh@invalid.ca> - 2020-07-21 19:52 +0000
    Re: Delay when SSH'ing into some systems in my LAN "S.K.R. de Jong" <SKRdJ@nowhere.net> - 2020-07-21 19:33 +0000

csiph-web