wrong mtu value on dsl connection

[Yigit Güneli]

Binary package hint: network-manager

i am using pppoe connection for internet. however, i cant visit some sites and i cannot use pidgin for msn on 9.04 due to wrong mtu value for ppp0. network manager sets 1492 as mtu value for dsl connections. if i use pppoeconf instead of network manager to set my connection, it gives 1488 and everything works as expected. i am now manually setting mtu with ifconfig ppp0 mtu 1488 everytime a make a connection.

and also trying to set the mtu value for my dsl connection with the gui of network-manager does not work, and it gives 1492 all time.

this was not a problem with 8.10, and i am not the only person affected on my network.

network-manager:
  Installed: 0.7.1~rc4.1.cf199a964-0ubuntu2

[Alexander Sack (asac)]

could you verify if the problem is gone in the packages in the ~network-manager PPA (https://launchpad.net/~network-manager/+archive/ppa) ... be aware that 3g has some minor problems in that snapshot, so if you need 3g, downgrade after testing. the rest should work fine though.

[Alexander Sack (asac)]

upstream bug: http://bugzilla.gnome.org/show_bug.cgi?id=572957

[Mathieu Trudel-Lapierre (cyphermox)]

We'd like to figure out what's causing this bug for you, but we haven't heard back from you in a while. Could you please provide the requested information? Thanks!

[Sergey Chebotar (s-chebotar)]

Well, i'm on Lucid and this problem is still here. When i tried Natty, it looks the same but i'm not sure, i downgraded because of some not related bugs.
With pppoconf configured connection, my ifconfig looks like

ppp0 Link encap:Протокол PPP (Point-to-Point Protocol)
          inet addr:46.175.126.109 P-t-P:89.16.99.229 Mask:255.255.255.255
          UP POINTOPOINT RUNNING NOARP MULTICAST MTU:1480 Metric:1
          RX packets:1099 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1088 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:3
          RX bytes:683704 (683.7 KB) TX bytes:138476 (138.4 KB)
With network-manager configured connection all the same but MTU:1492. And it ignores 1480 settings in network-manager GUI.
I tried network-manager from the trunk ppa. All the same.

[Istarion-rus (istarion-rus)]

In 11.04 problem still here. I solved this problem as follows:

sudo nano /etc/NetworkManager/system-connections/DSL (name of my connection)
go to section [ppp] and see what mtu = 1492. After changing of this value all good.

P.S Changing of MTU in GUI affect mtu record in section [802-3-ethernet], and this record has no effect for me.

[Thomas Hood (jdthood)]

Expired upstream. If this is actually still a problem then please reopen.

[vsespb (vsespb)]

Yes, this actually still a problem in 12.04. Not sure why upstream closed this.

[Graham Inggs (ginggs)]

I am seeing this behaviour in 14.04. MTU set to 1392 in GUI, but ifconfig displays 1492.

[Graham Inggs (ginggs)]

Editing the file /etc/NetworkManager/system-connections/<name of DSL connection> and adding the section below seems to work around the issue:

[ppp]
mtu=1392
mru=1392