Strange network problem! (Deja Vu for Spidey07 ;))

[Mucman]

We have an ethernet customer in our building. They are plugged in a Cisco 2924. They are one a seperate VLAN, and a 16 IP block. I get a
paniced call from them saying that their network is down. They couldn't ping their gateway but there was a link light showing (They had a DLink 8 port
switch). They said that they had tried to install a firewall and everyone went down after that. They said they had removed the firewall and set everything up back to the way it used to be. They still could not ping the gateway! I could ping their gateway from my machine.

They then connect a computer to the feed and it did not work. Suspescting the cable run, I hooked up my PC to their switchport and configured my
network settings like theirs. I could not reach the gateway anymore! I configured another switchport on the 2924 with the same settings and it started
working!

After working on this for 1.5 hours and go over there and inquire about what exactly happened. In his hand I saw a Linksys Router 🙂. It was not even
configured before he hooked it up to our feed! We have disabled proxy-arp, so that was not the problem. If I had cleared the MAC cache on the router would this have fixed it? (Instead of configuring a new switchport?) I would love to know why this killed the switchport.

Sorry Spidey07, but I did not stomp on their router because they are clients, not co-workers... and they are friends of mine.

 

[Mucman]

Up ya go

 

[spidey07]

did you take it out back and shoot it with a sig 45? 🙂

I'm a little on sure of your network setup, can you maybe provide some more details on the LAN and where a router comes into play and if that router is their one and only gateway?

Maybe something funny with VTP? Are you doing any trunking? Maybe clear the arp cache in the router. Default arp-cache is 4 hours.

 

[Mucman]

Nah, but I should have! I wish I knew it was a Linksys when the told us about the problem. When they phoned about the problem they told me they installed a firewall and it broke everything... they didn't mention that it was a router gosh darn it!

Unfortunately I am still learning about how our network works... I really need to fix my terminology but I can't pick up any Cisco books right now
because I can't put down the Wheel of Time series by Robert Jordan 🙂

The main net feed from the 7200 is connected to a 2948G. This is trunked to the 2924. This company has 1 switchport which goes to their office. The 7200
is their gateway. BTW, when this problem was happening I notice the 7200 was running at 30% when it normally is at 5%. Would doing a 'show running-config' bump it up?

Do you want the info on the trunk swithcports?

Here is their running config in the 7200

interface FastEthernet0/0.30
description UV Media
encapsulation dot1Q 30
ip address 66.51.175.1 255.255.255.224
no ip redirects
no ip unreachables
no ip proxy-arp
no ip mroute-cache
no cdp enable

Here is their swithport config on the 2924

interface FastEthernet0/1
description UV Media
switchport access vlan 30
no cdp enable

 

[Mucman]

Update! Is it possible that attaching that router could have blown that switchport? We tried hooking up another client to it with no such luck, moving
them to another switchport worked right away! The link light shows but now traffic flows (that is a cool rhyme 😉).

 

[ScottMac]

Perhaps there was a static electricity discharge. It's really hard to tell what could have caused it.

We've worked with some switches in the past that were pretty static sensitive.

I dunno...

FWIW

Scott

 

[Mucman]

Interesting, I just find it weird because a link light shows and it is able to auto-negotiate the connection properly... Are network cables really considered hot swappable?

 

[Tallgeese]

I've seen cases where lightning strikes travelled in such squirrelly ways, there was no rhyme or reason to what got damaged and what didn't.
We had a whole section of a hub (8 ports) where every other port was dead. All the others worked fine.

Static, a good spike (or brown), hits a path and who knows where it will go? Electricity has a mind of its own, and best to show it some HEALTHY respect

(this post mainly for the benefit of all those common sense-impaired individuals who keep asking about running copper data wiring exposed outside. AND doubly so for the misinformed doofuses who tell them there's no problem with doing it...:frown:

 

[Mucman]

TallGeese, I whole heartedly agree about running cat5 outside, but this was run indoors, and it happened when they plugged in the Linksys router! I guess electricity works in mysterious ways I guess.