GNOME Bugzilla – Bug 572957
MTU configuration of PPPoE not effective, not setup by default
Last modified: 2014-01-12 18:12:58 UTC
Please describe the problem: I'm using network-manager 0.7~~svn20081018t105859-0ubuntu1 (not the final 0.7.0). I configured my PPPoE configuration using the DSL tab in network-manager. It works fine for me. However I'm also doing NAT on this computer, and I now realized that the clients behind my NAT cannot access all the websites. For instance, microsoft.com does not work. After some research, it appears that I must configure on these clients the MTU to be 1492 before they can access internet. I did not have this problem before, when I used pppoeconf to connect to my PPPoE provider, because that tool by default suggests to clamp the MSS at 1452 bytes. Note that it is the default with that tool. The tool asks you but by default it will do the clamping. I think that network-manager should also do the same since it solves some problems (they also mention that it helps with some routers, too). Even if it is not the default in network-manager, I attempted to configure it by hand. In the "Wired" tab of the DSL configuration, there is a text entry "MTU". I set it at 1492 and also 1452 but it does not appear to help the connection of my NAT client computers. Steps to reproduce: 1. set up network-manager with a PPPoE DSL connection 2. set up NAT/masquerading/Internet Connection Sharing on that computer 3. connect from a second computer to internet using this NAT Actual results: Most websites work but www.microsoft.com doesn't (this is very serious because I believe it means that windows computer on my LAN will not get windows updates). Expected results: All websites should work by default if possible, in any case I should be able to make it work by changing some setting somewhere. Does this happen every time? Yes. Other information:
Created attachment 129398 [details] the helpful configuration page of pppoeconf suggesting the clamping
OK I made it work using network-manager by running this extra line for NAT: --append FORWARD --protocol tcp --tcp-flags SYN,RST SYN --jump TCPMSS --clamp-mss-to-pmtu So I guess in way you could close the bug WONTFIX and say that this is better handled by the NAT software, even though pppoeconf actually does this itself.
This report is pretty old. I guess when you manually configure NAT, you should also manually configure TCPMSS. But it might be valid if NM configured NAT itself.
For reference I'm the author and if I remember correctly, I configured the NAT with network-manager (that was the point). At that time I dropped pppoeconf and moved to network-manager for the NAT, if I remember well. but anyway nowadays i have a router and can't test this anymore. I guess everybody has a router nowadays and basically nobody does NAT with network-manager (if it's even still possible).
Thanks for your comments. I'll leave it as obsolete just in case anyone is going to re-test this in a recent version of NetworkManager.
Hello. Can we reopen this? Problem persists in Ubuntu 12.04 ==== network-manager: Installed: 0.9.4.0-0ubuntu4.3 Candidate: 0.9.4.0-0ubuntu4.3 Version table: *** 0.9.4.0-0ubuntu4.3 0 500 http://ru.archive.ubuntu.com/ubuntu/ precise-updates/main amd64 Packages 100 /var/lib/dpkg/status 0.9.4.0-0ubuntu3 0 500 http://ru.archive.ubuntu.com/ubuntu/ precise/main amd64 Packages ==== (ubuntu ticket https://bugs.launchpad.net/ubuntu/+source/network-manager/+bug/387456 ) I have ADSL and use it in bridge mode. My ISP recommends setting MTU to 1480. And it works better with 1480. > I guess everybody has a router nowadays and basically nobody does NAT with I have a router, but I turned it off to bridge mode, because it just works better and can keep more connections. Also, I think problem not related to use of NAT.