Cisco 677 and packet collision on small LAN

[Geddeth]

Hi,

I have a problem and a question. The problem is that in my local network, I have a 677 router working an ADSL connection, and behind that a simple dual-speed hub, which connects the LAN to the router. When only one PC is connected to the hub, it generates a heck of a lot of packet collisions - on its own. I find it strange and baffling. Any thoughts?

My question, which may be connected to the problem above, pertains to port forwarding in the router. If I would like to run an FTP server on a certain machine on the network, do I forward all requests from port 20/21 to only this machine's local IP, or do I forward them to every PC? (That goes for any port, that I would like to forward, by the way.) If so, how do I do that in the CBOS, without having to explicitly name every IP address on the LAN? Is there an argument that I can use instead of the local IP that means "all local IP addresses on the network"? What would happen, if I had two FTP servers on my network, and I forwarded inbound FTP requests to them both?

Thanks for any help you can supply.

Best regards,
Geddeth,
Copenhagen, Denmark.

 

[macanudo]

first of all, when you say 'When only one PC is connected to the hub, it generates a heck of a lot of packet collisions - on its own', are you referring to a particular box, or it is just a way to say that one machine connected at a given time?

if it is the former there might be a problem in the nic or in the hub (or a combination between them); but if the problem continues with any other machine/nic, then the problem is obviously defined within the hub.

regarding the forwarding issue, you have to redirect the inbound requests to the internal ip address of the server. that works for any particular service.

you can't do that with the same two services (like 2 ftp server) running on different machines, since you can't tell which request is addressed to each of them.
what you certainly can do is running similar services on different ports, that's been working for ages and is not a big deal.

hope this may help.

cheers, gabriel.

 

[Geddeth]

Hi Gabriel,

thanks for your reply. Regarding the collision problem - at the time of writing, I thought it to be a problem with the network. Thus, a single box on the LAN would generate collisions. After further investigation, however, I have learned that it lies with a particular PC. When it is connected to the hub alone, I get collisions, but only if the router is also connected. I have tried resetting the router and removing unecessary NAT entries, but to no avail.

Thanks also for the answer on port forwarding; it was as I assumed. I figured out how to forward to any internal IP with the Cisco router - using IP 0.0.0.0 solves the issue.

But the problem still persists. Any further fault-finding steps you can suggest? The box causing the problem runs Windows ME and uses a standard RTL8139-based NIC.

Thanks,
Geddeth.