Routers and IP Address FAQ

1. What is a router?

The routers sold by Lucas Valley Cable for use in our broadband services are special purpose devices that actually combine a router, a hub or switch, DHCP, and a firewall (and sometimes additional features or equipment) into a single unit. So to answer the question "What is a Router?" actually requires answering several questions.

Hub

A hub is simply a device that allows several computers to communicate with each other in the same manner as they would if they were on a physical bus. Packets coming from any computer plugged into the hub are sent to all other computers connected to the hub. Since each computer is given a unique address by its manufacturer (called a Media Access Control, or MAC address), orderly information exchange becomes possible. To actually effect useful communications, such as file or printer sharing, a common "protocol" must be "bound" to each computer, and these protocols also require that computers be given names to identify them on the network. Examples of protocols used on local networks include NetBEUI for Windows systems and AppleTalk for Macintosh computers (although computers of both platforms can load either protocol).

Switch

A switch is a "smart" hub. While the hub is completely hardware, a switch watches traffic passing through it to determine which computer is on which port. It then inspects each packet coming in on any one port and sends it out only on the correct port. Since a switch sends and receives information only on the ports involved in a given transaction, other transactions can pass through other ports simultaneously. This slightly improves its performance over a hub by reducing the possibility of collisions. In home networks, the 100 Mbps speed of the network is so fast that one is unlikely to notice any actual difference between a switch and a hub.

Router

When a network of computers wishes to have access to the Internet, an additional protocol needs to be "bound" to each computer requiring Internet access. The protocol used on the Internet it called TCP/IP, and the routers we sell are limited to that protocol. Unlike the protocols used for file and printer sharing, TCP/IP adds an Internet Protocol (IP) address to every packet. The purpose of the router is to examine every packet on a network and route it to the correct place. Because they can examine IP addresses, rather than just MAC addresses, routers are more powerful than switches. If one computer is communicating with another computer, the router ignores those packets whether they are TCP/IP or not. But TCP/IP packets that are involved with Internet traffic are passed through to the cable modem connection.

Network Address Translation (NAT)

Merely having a router does little in a home network, but equipping a router with NAT does a great deal because it solves an essential problem: every computer exchanging information on the Internet needs to do so with a separate IP address, but there is only one IP address per customer. IP addresses are a limited resource, so Lucas Valley Cable requires that each customer be assigned only one. NAT therefore becomes necessary when two or more computers share a single cable modem. When a router operates in NAT mode, it presents its own MAC address to the Internet rather than that of any of the computers in the home network. "Private" IP addresses are used on the home network to each computer and the router re-addresses every packet passing through the cable modem to the LVC system as needed in order to give each computer the illusion that it has a dedicated Internet connection.

NAT assumes that all connections are initiated by a computer on the local network. Packets coming from the Internet that are not part of an existing connection are dropped because the router does not know which computer might be listening for them. Most routers allow you to designate a computer to receive such traffic by setting up a "DMZ." Use DMZ with great care, however, as it bypasses a key defense against attacks of various kinds from unknown Internet parties.

Dynamic Host Configuration Protocol (DHCP)

When you use your computer to make an Internet connection, an IP address is assigned to that computer by a separate protocol called DHCP. In a dial-up connection, the ISP has a DHCP server and your computer acts as a DHCP client, requesting and receiving a "lease" to an IP address for a given period of time. Exactly the same function takes place when a computer is connected to a cable modem on the LVC system: the computer requests an IP address as a DHCP client and our DHCP server assigns one from the available pool that we have rented from our Internet supplier. When a router is inserted into this mix, it has to act as a DHCP client as well to obtain a lease to the single IP address that it will use to provide Internet connectivity to the entire home network. But it also must act as a DHCP server to provide private IP addresses to each computer on the network. The actual IP addresses on your network can usually be customized in your router's DHCP server setup screen.

You can also set up a network by specifying each computer's IP address manually, but you also need to specify a default gateway, a subnet mask, and the addresses of at least one DNS server. You should never have a combination of automatic and manual addresses unless you know what you are doing, because the router's DHCP might put two computer's on one IP on after a restart since it may not 'know" the IP's of computer that are configured manually.

Firewall

Having a network of home computers with access to the Internet also means having the computers themselves accessible to any other computer on the Internet. Unfortunately, not all computers are benign--some are operated by people intent damaging others, sometimes to steal information and sometimes as electronic vandals intent on doing damage for the mere fun of it. When computers are placed in a network for the purpose of gaining Internet access, good protection is obtained by simply turning off all networking features on all of those computers (file sharing, printer sharing, and "Microsoft Client.") But when the same computers have these features activated so that they can act as a local network, some measures need to be taken to protect against abusers. NAT provides a first line of defense, as any probing of your network will only "see" the router. Additional protective strategies are implemented in the router's firewall. Most experts these days recommend both a router and a software firewall.

2. Why do I need to buy a router if I have several computers?

The routers that are included in our product offerings contain several components that are fine tuned to solve the following problems:

They allow several computers to share one IP address (a requirement with which each of our customers has agreed by signing our Terms of Use agreement).
They prevent packets to and from computers in the home network from being passed on to the cable modem. You don't want those packets to go outside your network, and we don't want the congestion that they can cause on our system.
They keep "broadcast" packets from passing to the cable modem. Many LAN protocols generate frequent messages to enable other computers on the same network to be aware of their address.
They provide a firewall to protect your computer's information from unwanted and unauthorized access.

3. How can I find my IP address?

The answer to this question depends on whether you want the IP of your local computer or that of your router. Each computer's IP is different on a home network, but they all share the same router IP.

Router IP

You can get your IP by going to the Status page on your router, or you can use the whatismyip.com service. Router IP's for all plans above the Basic Plan are locked in so that we can provide an appropriate Quality of Service (QoS). If you change your router, make sure to let us know so we can make the necessary adjustments; otherwise your QoS will change and the quality of your service may suffer.

To get to your router's maintenance and configuration page, look up the Local IP (below) and take note of the default gateway IP (the default IP for most Linksys routers is 192.168.1.1). Enter that address into a web browser to log on.

Local Computer IP

Windows 9x: Click Start, then Run, then type winipcfg and OK. Select the TCP/IP protocol.

Windows XP, 2000 or NT: Click Start, then Run they type command. Enter ipconfig -all.

Macintosh with Open Transport: Open the TCP/IP control panel. Select "info."

Macintosh with MacTCP: Open the MacTCP control panel. Hold down the Option key and click the Ethernet icon.

4. How do I know a good IP address from a bad one?

If you are directly connected to your cable modem (or if a cable modem is integrated with your router), valid IP addresses are in the range 207.168.234.33 through 207.168.235.254.

When your computers are connected to a router, they are assigned IP addresses in the range extending from 192.168.0.0 to 192.168.255.255--a range of addresses reserved for use in local networks. Addresses in this range are not valid on the Internet and they will not cross router boundaries.

If you see an IP address outside of these ranges, it is not valid.

5. What about fixed IP addresses?

Customers with Internet plans above the Basic Plan level are entitled to a fixed IP address. These are associated with the MAC address of your router, which is therefore a part of our customer database accessible to you by logging on to the Support page.

Having a fixed IP address does not mean that DHCP is disabled. Rather, we configure our DHCP server to reserve an IP for the MAC address of your router. Therefore, if you ever replace your router, be sure to notify us. Few applications actually require that you maintain a constant IP, however your Quality of Service (QoS) depends on it. QoS sets the priority of your traffic in times of congestion, so it is important that you make sure that we have locked in the correct one. Changing a router causes the MAC address that our DHCP server sees, and that results in your getting the "wrong" IP address, resulting in a loss of QoS and the possibility of slower performance during times of high traffic.