sharing cabling for 2 networks

I've supported a small firm for a number of years, running NT4.0 Server and
giving them internet connectivity through a shared DSL router. They've now
sublet some of their suite to another firm and this second firm wants to set
up their own network. They don't want to share anything, because of a legal
need to have everything separate. Thus no shared server with the original
firm, no shared printers, no shared internet connection. Can I set up a
second domain on the same system of network cables? Thus the tenant would be
NewDomain, the original firm OldDomain. Neither firm should be able to see
the others resources. Each would have their own (different) ISP. In fact,
NewDomain is purchasing a fractional T1 whereas OldDomain is staying with
their longtime DSL connection. Or am I smarter to do a physical separation
of the two networks, adding a second small switch for NewDomain. There will
be two servers. Are there other issues I need to address? Like a firewall.
OldDomain has a 3com hardware firewall operating but that won't do NewDomain
any good, will it, since they're open to the net via different ISPs.

Thanks for your suggestions.

 

No need to run any new wiring or even new patch panels but If I were you I'd
add in a new switch and separate the two networks. It's a very cheap
solution to what could turn into a very expensive network to manage other
wise.

Dump all company A's runs into switch A and all company B's runs into switch
B. Once done there is now worry about one network seeing the other.

Now if the current switch is managed then you may be able to do it right in
the switch and avoid buying new hardware.

If you choose to use the same network equipment just make sure both networks
are on different IP subnets.

 

I would just put a second switch in which is dedicated to the new tenant
(IMHO...see disclaimer below).

 

You do not need to run any more cabling, but make sure
that their equipment is not connected in any way to your
equipment. If you do this, it will be two seperate
networks. If they are connected, network aware viruses
could spread between the two companies, not to mention
power surges going through the network cables which I have
seen happen quite a few times.