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I'm running a small business network, and the previous net admin allowed all services via a firewall management router. My question is whether there are any services that I should be blocking internally on the network (meaning LAN to LAN)?

My fears are that of virus infections being replicated across the network or even if (knock on wood) a hacker gets into a single PC now potentially has access to all resources within the network.

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In this context exactly what do you mean by services? Also, I'm assuming you're talking about the local firewall on each machine, as the perimeter firewall is of no use in blocking internal traffic. – John Gardeniers Jun 14 '11 at 0:20
@JohnGardeniers actually I did mean the perimeter router as well, but now realize that you're correct. However, I do also mean on each station as well. – KronoS Jun 14 '11 at 0:56
And the services of which you speak? – John Gardeniers Jun 14 '11 at 1:01
Any services @John – KronoS Jun 14 '11 at 1:08

We use the default settings for the built-in firewall on each machine. If a given machine needs to share something out of the ordinary with others on the LAN the appropriate change is made to that machine's firewall.

This approach has been fine in regard to restricting access to things by other users on the network but to be perfectly honest I can't see that it has had any effect in the two instances where we've had a virus infection on the network. I imagine that's because the viruses in question take advantage of security holes in the OS, rather than via published services. Of course this may well be very different for other viruses.

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