Effect on ssh of altering target's assigned ip address

[Cameron Simpson]

On 23Apr2009 12:15, Dave Feustel <dfeustel at mindspring.com> wrote:
| Everything seems to be working wrt the switch now. The problem I am now
| trying to resolve is why the initial windows load via ssh of XMaple
| takes 1 minute 38 seconds. Every complete repaint of the XMaple window takes
| approximately the same amount of time. This makes using X11 to run
| Maple an agonizingly slow process - too slow to put up with.

We should probably discuss this on the other thread, but ...

| > | So does a change of IP address for an ssh target affect the way ssh works?
| > | > You might also try "arp" to see if the IP<->MAC mapping is correct.
| > 
| > "arp -an" is the fast incantion to test.
| -------------------
|  2/home/daf}arp -an
| ? (192.168.6.1) at 00:22:3f:db:f3:90 [ether] on eth0

This lets you examine what MAC addresses the local host thinks other
hosts have. If you have access to the other host you can check for
correctness (eg using ifconfig).

|  2/home/daf}ssh -l daf $C4a

I presume '$C4a' is a shell var of your containing a host or IP addr?

| The authenticity of host '192.168.6.32 (192.168.6.32)' can't be
| established.
| RSA key fingerprint is af:6e:39:4a:4f:15:0d:ed:c9:01:06:e5:11:60:66:1c.
| Are you sure you want to continue connecting (yes/no)? yes
| Warning: Permanently added '192.168.6.32' (RSA) to the list of known
| hosts.

Fine.

| Password: 
| Last login: Tue Apr 21 12:57:12 2009 from 192.168.3.1
| motd

Ssh aborts here?

|  2/home/daf}echo $C4a
| 192.168.6.32
|  2/home/daf}

Try an "arp -an" now. Should be an entry for 192.168.6.32.

| Note that the ssh session terminated immediately after the successful
| login. This has happened several times this afternoon and I have no
| idea why. 

My first idea is that more that one machine on your network is using the
IP address 192.168.6.32, or that or your local host. This will cause
trouble. The exact behaviour varies with the OS, but it will include
aborted TCP connections (as the wrong host gets a packet and rejects it
as not being for a current connection).

| > Ssh keeps a ~/.ssh/known_hosts file that logs host keys and IP addresses
| > and host names in order to detect when things change (i.e. to check if
| > an imposter has arrived).
| 
| I deleted the known_hosts file to get rid of the entries with obsolete
| ip addresses.

Ok.

| > We would need to see the output of "ssh -v .....", but you should fix
| > ping first. If ping doesn't work, ssh almost certainly won't, and for
| > reasons having nothing to do with ssh itself.
| 
| Ping works fine now. Ssh works. It's just way too slow running XMaple.

I would now start using the "ethtool" command to examine the ethernet
interfaces on your local host and on the remote one. If, for example,
one end is half duplex instead of full duplex you will see horrible
performance problems much like what you describe.

Do I recall you're using a gigabit switch? Are you using cat6 cables
throughout?

Cheers,
-- 
Cameron Simpson <cs at zip.com.au> DoD#743
http://www.cskk.ezoshosting.com/cs/

These aren't the droids you're looking for.