multiple public ip adresses

I have a block of 5 ip addresses ending in 17 18 19 20 21
I am using a router with dd-wrt after a cable modem
we are putting an ip phone system in the office and the phone guy is connecting the cable moden to the phone server bypassing my own router.
is there anyway i can forward public IP to an internal IP address so I can use my own network instead of having 2 sets of wires
yammineyammineAsked:
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n4th4nr1chCommented:
Yes. It's called NAT and virtually every router and firewall supports it. If he's rigging it that way then of course you will have it that way. But if he will rig it through your router it should work. The thing is for voip you will probably want QoS as well.
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n2fcCommented:
I presume your phone server will be using one of the five static ip addresses...

Therefore, you should hook the WAN side of your router, the phone server and the cable modem to a switch,

You can then connect the remainder of your computers to the LAN side of your router (or additional switches attached to the LAN side of the router).
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Fred MarshallPrincipalCommented:
I agree with n2fc.  Somehow you have to figure out how you are going to get access to your block of public IP addresses. Here is one example:

The cable modem will have a public IP address that is one of your 5 addresses.  Connect it to a switch.  Connect all the other *publicly-addressed* devices to that switch.  Manually configure those devices with the public address that you want.

But your real issue is the wires, right?  
I don't know what kind of server the telephone system is providing you.  With highly secure VPN devices I allow them to bypass my "normal" internet firewall/gateway and connect from the internet to the LAN.  If the device can be trusted to block all but certain traffic then that may work for you.  But the "inside" addresses of the phone system will have to be on your LAN.

Another notion:
Most switches, etc. don't care what the subnet addresses are.  This means you can run multiple subnets over the same copper.  In my case I have this kind of setup:
ISP connection <> "Internet switch" <> Firewall and VPN devices <> "LAN Switch" .....
And, for example, when I have guests who are mostly trusted but I don't want to put them on the normal LAN, I add an internet router up there where it says "Firewall and VPN Devices" and give them their own LAN subnet which uses the "LAN Switch" and all the same copper and switches in the building.
So, if it makes sense the telephone LAN could be on a different subnet and still connect via the "LAN Switch" and following copper.  Eventually of course the phones have to have their own cables but maybe no different than any device/computer, etc.
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andrew1812Commented:
Static NAT - 1 one 1 mapping should solve your purpose
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arnoldCommented:
You have to make sure your cable modem is not NATing but rather passing the public IPs to your dd-wrt.
You would then have to configure your dd-wrt router to use static ips, and then use the networking tab under the setup to handle the public IPs on the one hand and then in the nat/qos section deal with passing traffic from the public IP to the LAN ip using 1 to 1 nat or port base
i.e. request on Ip port x forward to lan IP port Y
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