Definitions:For the purposes of this document, bridge and router, when applied to the device supplied by the ISP, have the following meanings.
BridgeA bridge supports a single IP address and serves to translate (bridge) between one transmission medium and another, for example, between TV cable and Ethernet, between DSL and Ethernet, or between Ethernet and WiFi.
RouterThe term router is misused slightly here to mean a consumer product that requires a single IP address on its outside (wide area network, or WAN) port and supports multiple client devices, each with its own IP address, on its LAN ports. To support multiple “inside” IP addresses, a consumer router necessarily implements network address translation, or NAT. It generally also provides DHCP configuration of clients and DNS forwarding. It could optionally provide a bridge between media types. It might provide other services, such as NTP relaying.
Although I've misused the term router slightly, my use here is consistent with industry practice and shouldn't confuse anyone. Strictly speaking, a "router" connects different networks, i.e. networks where the network part of the IP addresses are different. A consumer-grade wireless device does that, but also provides the other services listed above.
IF the ISP device operates in bridge mode then set up the wireless device as a router ELSE // The ISP device is a router, so Set up the wireless device as a bridge
So, the key question becomes, "Did the ISP supply a bridge or a router?"
Is the ISP device a bridge or a router?
Data CollectionRecord any manufacturer information or model numbers on the physical device. Google is your friend.
Connect a device running Microsoft Windows to a port on the ISP device, open a command window, and issue the command ipconfig /all
Find the section of output labeled Ethernet adapter Local Area Connection and record the following:
IP address: ___________________________
Subnet mask: _________________________
Default gateway: ______________________
DHCP server: _________________________
DNS servers: ________________________
Testing and InferenceAssumption: a device such as a laptop that’s plugged directly into the ISP device “just works,” so it was configured using DHCP and there’s a DHCP server someplace in the ISP's infrastructure.
- If there are two ISP boxen, the one connected to the TV cable or DSL line is almost certainly a bridge and the “inner” one a router. Consider the pair together to be a router.
- If there’s only one Ethernet connector on the ISP box, it’s probably a bridge. If there are multiple connectors, it’s probably a router.
- If the IP address from the data collection step is not one of the following, it’s almost certainly a bridge:
172.16.x.x to 172.31.x.x
- If the default gateway and DHCP server are not the same IP address, it’s almost certainly a bridge.
Acid TestIf there are multiple Ethernet ports on the ISP box, connect two client devices to two of the ports. If both clients work and report different IP addresses within the ranges listed in step 3 above to ipconfig /all then the ISP device is a router with probability one. Otherwise, it’s almost certainly a bridge.
If there’s only a single port, establish a configuration like this:
If both clients work and report different IP addresses within the ranges listed in step 3 above to ipconfig /all then the ISP device is a router with probability one. Otherwise, it’s almost certainly a bridge.