How to determine whether the optical modem is in bridge or routing mode? Don’t rush to change, look at these three places first

Last month, I added a router to my cousin's house. The newly purchased TP-LINK XDR6088 couldn't connect to the Internet when I plugged it in. I selected PPPoE in the setup wizard and filled in the broadband account and password correctly, but it still reported 691. Later, when I checked her optical modem, I found that the bridge connection had not been changed at all. The optical modem itself was still dialing, and the router should not have filled in PPPoE at all.

This incident taught me a lesson: Before changing the router, first find out whether the optical modem is in bridge or routing mode. If you make a wrong judgment, the router settings will be filled in for nothing, and the network that can be used may be broken. Today I wrote down the three places where I made my judgment. They are all very easy to find. There is no need to disassemble the phone or call the 10,000 number.

First look at the WAN port of the router. You can tell who is dialing at a glance.

The first step is the simplest, go into the backend of the router and look at the WAN port. You can see both things in "Internet Settings" or "Running Status" for TP-LINK and "Common Settings → Internet Settings" for Xiaomi: Internet access method and WAN port IP.

If the Internet access method says PPPoE and the broadband account is filled in below, it means that this router is responsible for dialing, and the optical modem is basically in bridge mode. At this time, the WAN port IP is usually a public network address, such as 223.x, 116.x, etc., not starting with 192.168.

On the other hand, if the Internet access method is "Dynamic IP" or "DHCP" and the WAN port IP is an internal network segment such as 192.168.1.x, 192.168.2.x or 10.x, then the optical modem is still dialing and sending addresses by itself, which is routing mode. This is the situation at my cousin's house. The WAN port of the router is 192.168.1.2 , of course I can’t connect to PPPoE again.

There is a pitfall that needs to be discussed separately.: Even if some broadband is bridged, the operator may still provide an address starting with 100.64. This is a large intranet created by the operator, not a real public network IP. Don't think that the optical modem has not been successfully bridged when you see 100.64. To judge the mode, you must combine the following two methods. I really don’t trust the public IP, I wrote about it How to check whether Telecom Broadband has a public IP , you can check it again.

There are also prerequisites for this move: You need to be able to enter the backend of the router. If the router has not been configured yet and cannot be accessed, then just look at the tricks in the backend of optical modem below.

Check the WAN connection table in the backend of optical modem. The final decision is Route or Bridge.

The second trick is conclusive evidence. Connect the computer network cable to the Optical Mode, and enter the Optical Mode management address in the browser. Telecom Tianyi is usually 192.168.2.1 , China Unicom and China Mobile are common 192.168.1.1 , a normal account will do. After entering, look for "Network → Broadband Settings" or "WAN Connection", and one or more connections will be listed there.

Look at the mode or type of each connection. What says "Route" or "routing" is the optical modem dialing, which is the routing mode. ； What says "Bridge" or "bridge" means that the optical modem only acts as a bridge, and the dialing work is left to the router behind it. This string of characters is the final basis for my judgment, which is more accurate than guessing the WAN port of the router.

The path of the Huawei HS8145V5 in my hand is Network→Broadband Settings→Internet Connection. When you enter it, you can see the mode column of each row. ； The ZTE F7015T menu will be moved. Some versions are placed in "Network → WAN", but they are all found around the words "WAN connection" and "connection mode". Some optical modem will list INTERNET at the same time._R and INTERNET_There are two lines B, R is routing, and B is bridging. The B line was probably added by the installer later. Take a photo of the entire page before moving it. What does each column on this page mean? I am What are INTERNET, TR069, IPTV and OTHER in the backend of optical modem? I’ve already discussed it before, so I won’t repeat it here.

There is another reality: Ordinary accounts can only be viewed and cannot be modified on some optical modems, and the WAN connection table is not even displayed at all. Only super administrator accounts can see it. Don't panic if you can't see it. It's enough to judge by the combination of the first and third moves. You don't necessarily have to go for super management.

Plug the network cable directly into the optical modem and try it once. Whether you can access the Internet is the final judge.

The third trick is actual testing, which is the stupidest and most reliable. Find a laptop and plug the network cable directly into the LAN port of the optical modem, not the IPTV port. After plugging it in, see what address the computer network card gets.

If the optical modem is in routing mode, the computer will automatically get the address of 192.168.xx, and the browser can open a web page and access it directly, which means that the optical modem is responsible for dialing and sending the address. If the optical modem is in bridge mode, you will either not be able to get a usable address when you plug it in to your computer, or you won't be able to access the Internet even if you get the address. You have to manually create a PPPoE dial-up in Windows and fill in your broadband account and password to dial up. In Win11, select broadband PPPoE in "Settings → Network and Internet → Dial-up → Set up a new connection".

When the address cannot be obtained, Windows will send a self-configured address of 169.254.xx to the network card, and it will definitely not work when opening the web page. Seeing the beginning of 169.254, you can basically confirm that this optical modem is not sending an address, and the possibility of bridging is very high.

When I dialed manually, I tried it on my old laptop at home. After dialing, the network card directly obtained the public IP address. Then I entered the same account and password into the router, and the router dialed up smoothly. It is equivalent to checking the bridge path for the router first.

This trick can also easily verify a common phenomenon: After bridging, optical modem's own WiFi is often still on and the signal is full, but there is no network connection because the dial-up has been moved to the router. My cousin stared at ChinaNet that time and couldn't get online. In fact, it wasn't broken, it was me. Will the WiFi still have network connection after the optical modem is changed to bridge? The situation written in.

Three "look-alike" exceptions, don't be led astray

In most cases, the above three tricks can solve the problem, but I have stepped on three pitfalls and singled them out.

One is China Unicom half bridge. Some Unicom optical modems have changed the bridge connection without deleting the original routing connection, but added a bridge connection. As a result, the router dial-up and optical modem WiFi can also access the Internet at the same time. At this time, when you see that the optical modem WiFi has a network, you will mistakenly think that it is still in routing mode. In fact, the line on the router is already bridged. I'm here How to avoid overturning when China Unicom optical modem is changed to bridge connection? Said it in detail.

Second, in the optical modem routing mode, the router is set to PPPoE. The result is that the call cannot be dialed and the number is 691 or 678, which is the same as broadband arrears. First change the router to a dynamic IP, which usually works immediately. If you forget the broadband account itself, you have to retrieve the account first. I wrote How to check if I forget my broadband account password? , you can flip it.

The third is property or dedicated broadband. Colleague Lao Zhang's broadband is a static IP provided by the property management. The optical modem is in routing mode, but the router cannot fill in dynamic IP. You have to manually fill in the IP, mask, gateway, and DNS according to the list provided by the property management. In this case, although the WAN port IP is in the internal network segment, the Internet access method is written as a static IP. Don't use it like ordinary families.

There is also a rarer hybrid binding: Using the same optical modem on the INTERNET_R and INTERNET_Keep both B and the LAN port of the optical modem to which the router is connected, and the connection will be completely different. In this case, just looking at the WiFi or WAN port will make you confused. You have to check which optical modem port the router's WAN port cable is plugged into, and then go back to the WAN connection table to determine the binding relationship. Ordinary families don’t encounter it very often, so it’s enough to know that it happens.

Once you've made your judgment, you're in the correct position, and you can just change it accordingly.

I have made a list according to the four most common situations, and you will not go wrong by filling it out.

summed up in one sentence: First look at the WAN port of the router to make a rough guess, then enter the WAN connection table of the optical modem to see whether it is Route or Bridge. Finally, plug in the network cable and give it a try. After completing these three steps, you will almost never make a wrong judgment again. The light modem menus in some provinces are very deep, and I really can’t find the WAN connection table, so I just use the combination of the first move and the third move to judge, and it’s enough.