Most run of the mill, home and small office routers provide dynamic network address translation (NAT). This enables the person setting up the network to connect multiple computers to a single internet connection. This is great if you only have a single external ip address (the ip address your ISP provides for you). It makes no difference if the external ip address is provided dynamically via DCHP or if it is provided statically.
Let me explain the difference between dynamic and static IP addresses even though it has nothing to do with this topic.
Usually an internet service provided with charge a premium for static IP addresses. That is because there are a finite number of them available. Most home office and small office end users do not really need a static IP address but many times people think it is easier to work with for whatever reason. As a result some people pay the extra charge for the assurance that the IP address from their service provider will never change. It really makes no difference if the IP address were changing every minute, the router behind the cable modem would take care of it.
A dynamic IP address changes from time to time according to the parameters set up by the ISP in DHCP (Dynamic Host Control Protocol). In most cases this will work just fine. The reason it costs less is because the ISP can use DHCP to manage its finite pool of IP addresses automatically.
But whatever is happening on the ISP side of the router has no bearing on Static or Dynamic NAT.
In most cases, the small office home office world the off the shelf router automatically sets up a dynamic NAT network without even asking. This works great as long as there is a one to many relationship between the external IP and the internal IPs. For instance you have a small office with a single IP from a service provider and you have 5 computers you want to network together. There is a one to many relationship between the external IP and the internal IPs.
But what happens if you have multiple IP addresses statically assigned by your ISP. Most of the time this happens in a datacenter, or server farm environment. This is not normally the case for small office home office situations, but some ISPs do provide business accounts with 2 IPs. Anyway, when you have multiple external IP addresses being mapped to multiple internal addresses that is when you need a router that will support “static NAT”. Static NAT sets up the router to handle the many to many relationship between external and internal IP addresses.
Not all routers support this. CISCO routers do, but they are aimed at the datacenter/server farm environment.
If you have a network problem and want to consult with someone who knows what to do send me an email at This e-mail address is being protected from spambots. You need JavaScript enabled to view it . Also Available via skype, username: KWBTech.
