brian wrote:
>
> I have a bizarre problem that I hope someone may be able to give me a clue in
> the right direction to solve.
>
> Setup:
>
> Work:
> I have 3 Linux-MDK8.0 PC's on my desk at work. All connected to same
> switch. A,B,C all have public static IP's can all ping each other and ssh
> into each other.
>
> Home:
> I have a 4th MDK8.0 computer, "D", at home with a publc static IP over an
> ADSL connection.
>
> Symptom:
>
> A,B,C can all ping and ssh into D.
> When I go home, D can not ping A,B,or C.
>
> Bizarre:
> If I leave a ping running from home for about 1.5 hours, A,B,C start
> responding to my pings. If I close all ssh sessions and stop pinging for
> approx 1 hour, and then try to ping from D again, the pings fail.
> If I get one of A,B,C to respond from D, I can ssh into it from D, then ssh
> to another computer of A,B,C, and then it will start responding to pings as
> well.
>
> Details:
> PC "A" is a Dell machine i bought and put Win2k/Linux on.
> PC's "B" and "C" are machines I built myself and have identical hardware.
> As I always customize the install, they have slightly different software
> loaded. They are running only Linux.
> PC "D" I built myself and is different than the other computers. It is dual
> boot Win2k/Linux.
>
> Troubleshooting:
> I replaced the existing Hub when the problem started with a new switch.
> >From D, I can ping 2 different Windows 2000 computers connected to the same
> switch in my office.
> Port Sentry was initially disabling me so I removed it from all computers. I
> want the problem to go away before I start more on security.
> I cleared all /etc/hosts.allow /etc/hosts.deny entries.
> I can't find any logs that show my pings being blocked, but I admit not
> knowing everywhere to look.
> I formatted/reinstalled Linux on all 3 computers at work.
> I can telnet from home into an old Sparcstation at the switch at work and
> ping A,B,C from it.
> I've replaced all network cables at work with brand new ones. I know they
> work because I can access the internet from A,B,C.
> I've verified that A,B,C won't respond from an another external location
> besides my home.
>
> Help! I have to get these working. B,C will be web/email servers that won't
> be much good if I can't ping them from outside my office.
>
> Thanks to anyone who can help!
>
> -Brian
Sounds like you may have a [corporate] firewall between home & office. There
may be a problem with the firewall, or an intermittent alternate path around the
firewall.
Assuming the number of hops between [A,B,C] and D is less than 9, you can try
"ping -R"** from D and when the replies start coming in, see if the recorded
routing information is as expected... Also, compare the responses to see if you
are getting different routing on the individual pings.
** won't work through a LinkSys
Note... traceroute is not the same... it tries to discover a path from X to Y
by probing 1-hop deeper on each attempt; but may not discover all the alternate
paths which may exist, or find intermittent paths. "ping -R" records the path
(outbound interfaces) it really took as a packet "to" and the reply "from" which
may be different paths since routing is not guaranteed to be symmetrical.
HTH,
Pierre
