HELLO & WELCOME

[VoipIT]

I'm using my Huawei B628-245 on the Three network. My MTU needs to be set at 1440 but there is no option to change the Mobile Internet Connection MTU on my router? *Bleep*!!!
(To find out your ideal MTU setting, refer to this this post.)

After some searching on the internet I discovered that there is a way to find out the current MTU Setting the modem is using. Just copy and paste the following code into our web browsers developer console (Refer to step 3 of this post) while logged in to the device:

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getAjaxData('api/dialup/connection',
  function ( ret ) {
  console.log(JSON.stringify(ret))
})

This will return a JSON object which has various parameters for the modem including the MTU as shown below:

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{"type":"response",
  "response":{
    "RoamAutoConnectEnable":"0",
    "MaxIdelTime":"0",
    "ConnectMode":"0",
    "MTU":"1500",
    "auto_dial_switch":"1",
    "pdp_always_on":"0"
  }
}

As you can see from my result above, the default MTU value is set at 1500 on my device.

Unfortunately there is no way of changing the modems MTU setting through the routers GUI or your web browsers developer console. However, we can change the routers default MTU using node.js and Huawei Router API. Just follow the steps below:

1. Install node.js from here.
2. Go to this page and click on the green "Code" button and click on "Download Zip".
3. Locate the ZIP file and Unzip the file.
4. Using terminal/command line, navigate to the Huawei_router_api_master folder that you just unzipped.
5. Run this command:
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   npm install

6. Now run the following command:
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   npm run build:node

7. Using a text editor such as Notepad++, create a file in the Huawei_router_api_master folde called index.js and paste the following code inside it:
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   const router = require('./dist/index.cjs.js')
   
   router.config.setUrl('http://YOUR ROUTER IP');  // replace with your IP
   router.config.setUsername('admin');
   router.config.setPassword('YOUR WEB PASSWORD'); // replace with your web password
   
   var mtu = process.argv.slice(2)[0]
   
   console.log(mtu)
   
   if (!mtu) mtu = 1500
   
   async function checkConnection() {
     // Check if we are logged into the router already
     const loggedIn = await router.admin.isLoggedIn();
     if (!loggedIn) {
       // If we aren't, login
       await router.admin.login();
     }
     const stats = await router.dialup.getConnection();
   console.log('Current settings')
     console.log(stats);
     return stats
   }
   
   async function setOptions(options) {
     // Check if we are logged into the router already
     const loggedIn = await router.admin.isLoggedIn();
     if (!loggedIn) {
       // If we aren't, login
       await router.admin.login();
     }
   
     var APIoptions = {
       roamAutoConnectEnable: Number(options.RoamAutoConnectEnable),
       maxIdleTime: Number(options.MaxIdelTime),
       connectMode: Number(options.ConnectMode),
       mtu: Number(options.MTU),
       autoDialSwitch: Number(options.auto_dial_switch),
       pdpAlwaysOn: Number(options.pdp_always_on)
     }
   
     //console.log(APIoptions)
     const stats = await router.dialup.setConnection(APIoptions);
     console.log(stats);
   }
   
   main()
   
   async function main() {
   
     var config = await checkConnection();
     config.MTU = mtu
     await setOptions(config)
     await checkConnection();
   
   }
   

   (Replace YOUR ROUTER IP with the IP address of your router and YOUR WEB PASSWORD with your web GUI password.)
8. Finally run the script you created in step 7 to set the MTU with the following terminal command:
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   node index.js 1500

   (Replace 1500 with whatever MTU setting you want - Values below 1400 and above 1500 will throw an error.)
   The script will report the settings twice, once before setting the value and again once the MTU setting has been set so that you confirm it has worked.
9. Restart the router for the setting to take effect.

That's it! You have now successfully changed your routers default MTU from 1500 to whatever value you entered in step 8.

Note 1: Dropping my MTU down to 1440 has solved the occasional page loading problems I have been experiencing while testing out my installation.
NOTE 2: The MTU setting was added to the Three UK software version, I wonder whether this is something that they were expecting to cause problems?

[@UKVoIPForums]

A very informative post @VoipIT!

For anyone using a MAC you can use the following to work out your ideal MTU:

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ping -D -s xxxx www.bbc.co.uk

I got to the figure 1464, anything higher and things fragment, and I get timeouts. So, my ideal MTU is 1492!

The reason I use 1492 is because we need to take the headers into account which take up 28 bytes. Therefore, the MTU is the highest value that can be sent without fragmenting +28 - in my case 1492.