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Static IP address on Cisco 752

I understand DHCP, that DHCP server hands out IP addresses.

What if router has static IP addresses (the way Cablevision does it with their Business class customers).

The Cisco 752 has five ports which are pre-configured and locked down with static ip addresses.  If I attach a laptop with a crossover cable and plug into the port, I should be able to get out to the internet if I configure the laptop NIC with the same static ip address that I'm plugged into.

How does this work?  What causes traffic to be forwarded from the NIC on the router to the NIC on the laptop.

If the NIC has the static address I would think traffic would stop there.  Is this just some kind of passthru?  How can I find out more info??
1 Solution
Don't use a cross over. Use a straight cable and configure your laptop with an IP address from the same range as that NIC on the router, and use that router's IP as the gateway. you should be able to get out to the net.
Of course, the router should be plugged into the ISP and you should be getting to the net from the router first for the above to work
Istvan KalmarCommented:
If the router use proxy arp is it working:


it means router answer all arp entry, and solve for your laptop the defaul gw....
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supportorangesAuthor Commented:
Thank you for your quick response.

What confuses me is this.

There are four ports on this router which are configured for static IP.  Each one of the ports comes preconfigured with a static IP.

I know I have to configure my laptop with the same static IP that I am plugged into.  It seems that both NICs (the one on the PC and the one on the router) will then have the same IP address.  Does this work because the static IP port on the router is just functioning as a passthru.

My fixed concept is that every machine on the internet needs a unique IP address.  I don't get this scenario.  Am I overcomplicating?
Preconfigured? Are you using that router's ports as a hub, or separate segments?
I don't think you want the IP addresses to be the same - you want them in the same subnet, right?
supportorangesAuthor Commented:
Separate segments.

Let me give you some background.

I am planning on the migration of a mail server from a different geographic location.

Before I physically move the server I want to make certain I totally understand how these static IPs are working.

Optimum Online for business offers their business customers a Cisco 752 router with 5 Static IP addresses.  each port on the 752 is binded to a Static IP address.  The Cisco gets Internet from a regular cable modem.  

Optimum Online may be doing something special because I am hearing rumors that it isn't "real" static IP, but a weird kind.  The Cisco gets attached to a modem.  I know from experience that I can plug a laptop into the modem and get a dynamic IP address (which is what the Cisco does).

The Cisco somehow spreads out the connection to five static IP addresses.  I am seeking to understand how all this works.
supportorangesAuthor Commented:
The IP is still dynamic, it's just assigned and provisioned to the mac id of the Cisco router/modem... The tech provisions the modem/router by logging into it thru telnet and telling it not to use it's own dhcp server, and locks the ports to their respective ip address so that a machine with the ip statically assigned can use the connection, when configured right...


The comment courtesy of the above forum.  Any comments before I close?  The narrative above explains to me how a machine configured with a static ip address can use a port configured with the static ip address.  Is this normal or unusual?
supportorangesAuthor Commented:
Thank you.  What's weird is that Optonline says it doesn't matter what physical port you plug into.  You will get the static IP you ask for.

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