I recently installed a new 2820 router into a business and connected it to a newly provided adsl. I then setup a vpn to a single pc. All working ok.
The business now wants to cease their other adsl service, which supplies b/band via a 3com multiport switch/hub to seven ethernet sockets in the building, and instead have me connect the new b/band service, at present only used by the vpn, to the 3com system and then to all the pc's in the building including the vpn server pc.
I do not pretend to be an expert on networking but get by ok as per the vpn. However I would appreciate some help on a couple of points:
The 2820 is not in the same room as the 3com so to save having to relocate the adsl input socket can I keep the pc used by the vpn connected directly to the 2820 as it is now and send a feed from one of the other ports on the 2820 to the 3com via existing internal ethernet and then to the other pc's? There are a couple of other pc's in the main office. Can I connect them to one of the other ports on the 2820 via a netgear 4 port hub once again saving the need to run additional cat5? If the business decides to make use of all this to fileshare across the system(s) instead of just internet access as at present will that be possible with the layout I have described or would there be too many subsets?
Will I need to configure the pc's for static ip addresses?
Will be very grateful for any advice.

What you're saying sounds OK.

What does the 3Com switch/hub currently connect to to get to the internet? Presumably there is a modem somewhere and something (possibly combined with the modem) to give out DHCP and perform NAT/Routing.
Is the 3Com unit a simple switch/hub or is it a managed device? If it is not managed it should be fairly straightforward.

You should be able to connect a 3Com port to any LAN port on the 2820.

You can use the other 2820 LAN ports directly to other PC's or via a switch or hub (a switch is preferred to a hub) to other PC's.

You do not need to use static IP addresses. They do have some advantages but are more hassle to set up. If you only need a few, have a look at the Bind IP to MAC facility which means the DHCP server will always hand out the same IP to a particular PC.

File sharing with your setup should be fine. It is easiest if you make sure all the PC's are in the same Workgroup. If you do not do this it will be better to have static IP's or all IP's bound by MAC address to the DHCP server.

Thanks NJH for your advice.
I have a feeling that the 3Com switch is a managed device...I will not know for certain until I go back to the site tomorrow.

At present the 3Com receives its adsl input from a simple Belkin 4 port wireless router. Two of the 3com's outputs are connected direct to individual pc's and a third port feeds to a socket into which is plugged a Netgear 4 port hub and this has two outputs to two pc's. The only purpose up to date has been to supply all these pc's with b/band but as I said in my original post the business wants to be able to take advantage of a lan with b/band and file-sharing.

So if I connect one port of the Draytek to the 3com to supply it with a b/band feed and then the various outputs from the 3com should provide lan/adsl to the connected pc's and also if I connect one of the other 2820 ports via the Netgear to the other two pc's I should be able to give all the users file sharing across the lan and internet access? What problems might I face if the 3com is a managed device?

Many thanks once again for your help.

If the 3Com unit is a managed device, I cannot help you. I have no experience of them at all. Having said that, they are normally for high end use and therefore (very) expensive. I get the impression that your network is pretty basic so I would not be surprised if the 3Com was not managed.

Doing what you describe should be fine. When you remove the Belkin and cable in the Draytek, you will either need to re-boot each PC or do an "ippconfig /release" then "ipconfig /renew" from a command prompt on each PC.

Great news...all is now working ok. Help & advice much appreciated.