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Groups > comp.os.linux.networking > #4673

Delay when SSH'ing into some systems in my LAN

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	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

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.

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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

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