2610 LAN configuration with devices on both internal and external IPs

Unanswered Question
Oct 27th, 2009

I am more than a bit rusty and reconfiguring a network due the arrival of a new SBS office server. The new office server (and clients) needs to connect to the Internet via our Cisco 2610 router. The server is say and the FastEthernet0 interface on the router is set to The 2600 has a Serial0 interface that is connected to a leased line with an external IP address. We also have our own class C IP range used for web, mail and dns servers.


OfficeServer (<----->FastEthernet0([2600 ROUTER1]Serial0(<---leased line--->ISP(Internet)

However, I also have a webserver etc in our office, with an external IP address from our range, that needs to, and can, see the Internet.

So, we also have, on the same router:

WebServer (<----->FastEthernet0([2600 ROUTER1]Serial0(<---leased line--->ISP(Internet)

interface FastEthernet0/0

ip address secondary

ip address

ip nat inside

speed auto



interface Serial0/0

description Connection to NTL

ip address

ip broadcast-address

ip access-group inboundfilter in

ip access-group outboundfilter2 out

ip nat outside

encapsulation ppp

no fair-queue

The FastEthernet0 interface has both an internet and external IP address mapped to it. Currently the office PCs use the external IP address as their gateway address and this works, however the new server is more secure and won't allow this.

There is NAT and access-lists running on the Cisco and each office PC has an internal IP address that is NATted to a dedicated external IP.

At the moment the webserver can see the Internet, but the office server cannot. Office PCs can see the Internet if they use the external IP address mapped to FastEthernet0/0 direct as their gateway address (although you get a message suggesting that this is not the way to go). So I am trying to resolve this whilst also trying to set it up better/properly.

What is the best way to do this (all assistance appreciated)?

Do I need to NAT the internal office server IP to an external IP address for it to see the internet?

Do I need to NAT the internal gateway address to an external IP address or will the router be able to route this anyhow?

Could it be DNS, so should I set the DNS server on the office server NIC to the ISPs DNS server, or to the Cisco

I have this problem too.
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