I was told to change the MTU setting of the Actiontec, so it will work with my Xbox. How do I change the MTU?

There are problems with doing this.
The MTU setting is not the cause. The default MTU setting for Actiontec routers is 1492 for PPPoE connections, and 1500 for DHCP as well as Static connections. To change the MTU setting, log into the Actiontec device and adjust the MTU settings as required. (But, the MTU setting is rarely ever the problem.)

The actual problem is that the ports used by the Xbox, are not open for incoming traffic. There are two ways this can be changed.

  1. Enable UPnP (Universal Plug and Play). Many of our routers and modems are delivered with UPnP disabled for security reasons. Make sure the Xbox is properly configured for networking. The Xbox should be configured as a DHCP client, with a proper HOST name and UPnP needs to be enabled.
  2. The other way is to open the ports needed by the Xbox, using the Port Forwarding or Applications Forwarding features of the Actiontec device.
  3. Use the DMZ hosting feature in the Actiontec device instead of Port Forwarding or Applications Forwarding. This will put the Xbox outside of any firewall controls of the Actiontec device and open ALL incoming ports to the Xbox.

Note: DMZ Hosting, Port Forwarding or Applications Forwarding can NOT be used at the same time for the same device. It may also make your network accessible to intrusion.

If the problem persists after using the above steps then the issue is MAY NOT be with the Actiontec device but will be either an Xbox Service or the Xbox console itself.

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8 comments
  • I have a Actiontec C1000A. I have studied the configuration screens while logged into the modem. I do not see a way to change the MTU. Can the user configure the MTU in this modem?

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  • Dave,
    The MTU settings should be adjustable by users. It is not recommended as the settings are preconfigured for best settings already. If you are having issues finding the setting you will need to contact CenturyLink support at 800-247-7285.

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  • Again, I have found no option in the Century Link (CL) C1000A modem to change the MTU setting. My guess is Actiontec or CL loads custom firmware into these modems. Have you actually seen one of these modems - a C1000A loaded with CL firmware? I think you are confusing others by saying the MTU setting should be adjustable. OK where do you make that change in the GUI? If you want to help - get one of these CL modems and try changing the MTU setting yourself. I am working with Cisco on some VPN problems and they are recommending I lower the MTU value.

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  • Dave,

    The MTU settings are in the advanced setting page under broadband settings. The reason we asked you to contact CenturyLink to change these setting is because these setting are configured to optimize your connection with the CenturyLink network. If you change them it may effect your internet connection but only CenturyLink can tell you that information and this is why we directed you to contact them.

    In my experience issues with MTU settings need to be the same as your ISP because if they are not you will start to have fragmented packets and that will cause you issues. I mean Cisco may know there equipment best but like I said the ISP set those settings for a reason. So before you change them I would speak with your ISP first.

    I would look more at your port forwarding settings for this issue. I would remove all rules under port forwarding and enter them under applications forwarding in the advanced setting page instead. Actiontec can help you with this but the CenturyLink tech has to call us on their tier 3 line and the tech has to stay on the call.

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  • I found the place to change the MTU in the Broadband settings for the C1000A. The MTU value is currently at 1492. Any setting I tried less than 1492 dropped the ISP (CL). A setting like MTU = 1500 also dropped the ISP or lost the internet connection. I have heard that the 1492 setting is so CL can support PPPoE. The problem found by Cisco is when their VPN client sends a packet to the C1000A router with DF set (don't fragment) and MTU 1500 - the router sends back an ICMP message Destination Unreachable per RFC1191. This makes sense since the next-hop has MTU 1492. This back and forth is not efficient and Cisco believes may cause their VPN connection to time out and drop. So, there is a reason why they recommended changing the MTU at the router. I am working on testing with a lower MTU setting on the network interface now.

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  • Dave,

    Unfortunately that is not something we can't answer, this is why we need the CenturyLink tech on the line during a call. Did you look at the port forwarding we talked about earlier or is there no port forwarding configured?

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  • I found the port forwarding setting in the C1000A. But I don't understand how this
    solves the MTU mismatch problem I am having between CL and the Cisco Anyconnect VPN client.

    I have not been able to get anyone from CL that is technical and could offer some help on this issue.

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  • Dave,

    We saw a similar issue with Xbox hence why the article above was created. Xbox kept telling its users to change the MTU setting on there modem to fix the issue they were having with not being able to play online. When in the end it was a port forwarding issue where the ports that the Xbox required were not open correctly in the firewall. Which is why I suggested you look at the port forwarding first before trying to change MTU settings that I was almost certain would disconnect you from your ISP. Did you look at the port forwarding did it fix your issue?

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