Why mapping Static External IP to Static Internal IP?

[albert]

Maybe someone can give me some advice on a non-Jaguar issue.

I have an executive office space where the tenant manages all the computer infrastructure for the complex. I pay an additional fee for a static IP address. What they have done is assign me an Internal Static IP 192.xxx.xxx.xxx. They then mapped an External IP to it 75.zzz.zzz.zzz which enables me to access my router when outside the building. Inside the building I have to use 192.xxx.xxx.xxx. Why would they do this, should I complain? Isn’t mapping the external IP straight through more ideal allowing me to use it whether I am in the building or outside?

Another thing they did was link my MAC address to the IP, since they have told me any change in my MAC address will cause problems. What is the pro’s and con’s of this to me?

Let me know if you have any input.

[jason]

IP addresses are assigned geographically in what are called subnets. Each subnet is a specific group of IP addresses. Routers keep track of where these subnets are located and route packets (pieces of information) based on that information. So you can't just arbitrarily start using an IP address somewhere and expect it to work.

The 192.168.x.x block is reserved for non-public use. In other words, no traffic in the 192.168.x.x address space is ever supposed to hit the public Internet. Originally the 192.168.x.x block was set up for testing and experimenting, but with the rise of new technologies such as Network Address Translation (NAT), supply and demand issues with IP addresses, and just general security it has become common to set up internal networks in this address space. The networks don't have direct access to the public Internet, instead connect to a router that essentially serves as a proxy between the public network and the individual computer.

Since your office is already on the 192.168.x.x netblock they can't just assign a single external IP within it, so they have to sort of jump through a hoop to make it work.

Your MAC address is an address "hard coded" into your network card. The MAC is used in the physical network layer to determine which node is supposed to receive a particular packet. Your office is most likely using DHCP (Dynamic Host Control Protocol) to assign IPs--when a computer connects to the network a DHCP server assigns an available IP to it. In order to assure that a specific IP is always and only assigned to a specific computer it needs a unique identifier to identify the computer and the MAC address is it.

--Jason

[thecoalman]

Another thing they did was link my MAC address to the IP, since they have told me any change in my MAC address will cause problems. What is the pro’s and con’s of this to me?

No expert on the issue but that's standard practice for cable ISP's. It's how they determine if you're legitimate user. For example locally we have cable internet, you can go buy a modem and connect to the network through the same cable supplying your TV.

I believe they throw up a standard "self-installation" page. You won't get by that because they have no record of the MAC address for the modem. If you buy your own modem such as I have done you need to give them them the MAC address before it will work.

[JPC-NickO]

Hi Albert,

They've configured a Symmetric NAT for you.

The benefit to this is that you could have multiple devices attached to your internal switch which you could access from all of your internal devices without requiring a static IP for each device.

The other solution would be to assign multiple IP addresses to the computers with a Internet route-able (public) IP address.

The reason why they 'linked' the IP address to the MAC address is likely just for ease of configuration.