Is my switch definitely broken?

November 9, 2010 at 01:18:56
Specs: Windows XP
My network PCs all have manually set IP addresses in the right range to see each other. Suddenly this morning I'm getting strange behaviour like this:

a) It's not symmetrical - i.e. X can ping Y, but Y can't ping X.
b) It's not transitive - e.g. X and Y can both ping Z, but X cannot ping Y.

This is happening with seemingly random PCs.

I reduced the network to simply switch + PCs (with static IP addresses). No firewalls. I've tried changing cables and sockets, but it doesn't change anything.

My question is: Is the switch definitely broken or can this behaviour have another explanation? We are way out in the African bush and it is not easy to replace it, so I want to make sure!

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November 9, 2010 at 05:08:45
This is a tough one.

Typically, if a switch, or a port(s) on a switch fail then they stop working, period. I have an older Cisco 2900 XL 24 port sitting in my home office I grabbed from work. It has 5 bad ports that don't work. When I say "don't work" I mean, don't work at all. But all the rest do work properly so I can still get use out of it at home, but it's definitely never going to go back into production at work.

a) It's not symmetrical - i.e. X can ping Y, but Y can't ping X.

To be honest, this sounds more like a software firewall issue than anything else to me.

Try moving both to completely different ports on the switch. If the exact same behaviour continues, then it's not likely your switch but is more likely software related.

It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.

***William Henley***

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November 9, 2010 at 09:50:52
post an ipconfig /all from X and Y for review

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November 9, 2010 at 21:33:21
Thanks for the replies. They gave me confidence to go back and re-investigate the software settings and... doh! It seems that Windows XP has some events that re-activate its firewall without telling the user. I disabled the firewalls again and it works.

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November 10, 2010 at 06:04:28
consider reengaging the firewalls but configure them to allow file and print sharing.

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