Need networking help

We are having problems in our building - internet access on only two of our ten computers on the first floor.  No internet access for computers on the second floor.  Second floor computers can map to the network.  The computers on the first floor cannot map to the network.

I brought in our phone service provider to check the router leading out to the internet - he says everything is ok with the router.  

I have re-sent every switch in the building; re-started the network - no luck.  What else can I try?  We have cat5 wiring.

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JeanHoltonAuthor Commented:
The solution to this problem was that the IPSEC service had stopped.  Restarting the service resolved the problem.
John MeggersNetwork ArchitectCommented:
Lots of variables here.  How many VLANs?  If more than one, what's doing inter-VLAN routing?  What kind of routing -- static or dynamic?  Is the Internet gateway advertising a default route into the network?  Are there any ACLs in place that are blocking traffic?  All these things (and more) can impact network traffic.  Then there are other issues regarding name resolution, such as the lmhosts file, etc.

One question, when you say some computers can "map to the network" do you mean they can map drives to network servers?

My suggestion would be to start from one of the hosts that's not working and work your way towards the Internet at the IP layer.  What address is the host using for a default gateway?  Go to that gateway, see what he thinks his routing table has for an Internet route, that is all unknown destinations (meaning not explicitly listed in his routing table, typically showing up as  Make sure he has a route to where the servers are.  If it's true the Internet router is OK, then there's something going on behind the router that's affecting Internet traffic.

If you have some hosts that work and others that don't, clearly there's something different in how things are set up, but that could be on the host, or it could be in the network (e.g., access lists). You can also check MAC address tables to make sure switches in the network know where to send traffic at layer 2. Once you've established that all the direction signs are working properly at layer 2 and layer 3, you can address issues regarding protocols (NetBIOS) between devices, name resolution, etc.
JeanHoltonAuthor Commented:

The computers on the first floor cannot map drives to the network servers, which are located on the second floor.

Upon further examination, it looks like the internet and network connections are coming through one switch in the warehouse on the first floor.  We replaced the switch with one that we know works - did not resolve problem.

There are two computers on the first floor that can access the internet.  It looks like they are connected without going through the switch.  We would have to go up on a ladder to see.  We have a technician coming out today.
JeanHoltonAuthor Commented:
Reason for choosing own response - I had a technician come in and he came up with the solution.
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