NM 0.7 doesn't automatically apply correct MTU setting

[Jonathan]

I just installed the Intrepid beta and I cannot load many websites that other computers on my home network have no trouble loading (including one computer running Hardy 8.04).

My router's (Netgear WGR614) MTU size is set to 1492. Websites load properly after manually applying an MTU size of 1492 bytes or lower:

       sudo /sbin/ifconfig eth0 mtu 1492
       sudo /sbin/ifconfig wlan0 mtu 1492

This is my first Ubuntu bug filing, so please let me know if I'm missing something.

[Rich (rincebrain)]

Are you explicitly sure that this is linked to Intrepid vs Hardy, and not external factors (e.g. your internet connection, someone else on your network)?

This sounds like behavior from being near the connection limit on a card.

What machine is this - what are the wired and wireless cards on the machine?

[Jonathan (jonathanmotes-gmail)]

It is a Dell 1420 Inspiron laptop.

From lspci:
Ethernet controller: Broadcom Corporation NetLink BCM5906M Fast Ethernet PCI Express (rev 02)
Intel Corporation PRO/Wireless 3945ABG [Golan] Network Connection (rev 02) - I replaced the Broadcom one with this one.

I suppose since my internet worked with Hardy then Intrepid should be able to make it work also. I currently have a desktop running 8.04 with no problem.
Desktop's hardware: Ethernet controller: Intel Corporation 82801BA/BAM/CA/CAM Ethernet Controller (rev 03), if that helps any.

[Jonathan (jonathanmotes-gmail)]

I found a solution! Turns out my original attempt at modifying the MTU size was flawed.

Running the line below completely solves the problem:

    sudo /sbin/ifconfig wlan0 mtu 1492

Now, how should the developers go about fixing this? Is simply lowering the MTU size a reasonable permanent solution?

[Jonathan (jonathanmotes-gmail)]

I found out that the MTU size on my router (Netgear WGR614) is set to 1492 bytes. If my network card uses anything higher than 1492, I have problems loading web pages.

I guess this means that network-manager is not detecting and/or applying the router's MTU setting.

What do I need to do in order to get this bug confirmed? One person who posted on my ubuntuforums thread had the same problem as me (and most likely the same hardware).

Should I close this bug and create a more specific one?

[tomten (fredrik-corneliusson)]

In 8.10 I got significantly slower maximum internet network connection speed (5mbps instead of 10mbps).
I found out that network manager used a automatic MTU value and it seemed to choose a lower MTU size than previous releases (about 500 in this my case). Is there any reason for it to use a lower MTU size than previous releases and Windows XP?
I changed MTU to 1500 and now I have the same speed as in Windows and previous Ubuntu releases.

To make matters worse there is a bug (Bug #278216) in network manager configuration that keeps it from saving the setting between reboots if you do also change something in the IPv4 Tab (reported as another bug) but that's a whole other story....

[eternalardor (eternalardor)]

I can confirm this. I have had this problem both at my University and at my home. At both places my connection worked perfect under XP and failed to work under ubuntu 8.10. As soon as I manually set the MTU value to 1492 (and then disabled and enabled the connection) everything worked fine.

[Brian Murray (brian-murray)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. Could you please add your '/etc/network/interfaces' file and your dhcp lease file from '/var/lib/dhcp3/dhclient.eth0.leases' without the MTU manually set? [N.B. eth0 will need to be the name of your interface.] Thanks in advance.

[eternalardor (eternalardor)]

Ok, I didn't have a '/var/lib/dhcp3/dhclient.eth0.leases' file but I did have a '/var/lib/dhcp3/dhclient.leases' file.

Other then that here they are.

[eternalardor (eternalardor)]

ok actually launchpad won't let me upload the '/var/lib/dhcp3/dhclient.leases' file because it says its empty and sure enough when I open it with a text editor it is empty as well.

[PasQty (pas-i)]

hey.
i was fighting with that to. so now i have:
in /etc/network/interfaces
[...]
# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
#auto eth0
#iface eth0 inet dhcp
# MTU 1496

and in /var/lib/dhcp3/dhclient.leases (in windowed NetworkManager i have manually set MTU 1500)
lease {
  interface "eth0";
  fixed-address 192.168.0.11;
  option subnet-mask 255.255.255.128;
  option routers 192.168.0.1;
  option dhcp-lease-time 86400;
  option dhcp-option-overload 3;
  option dhcp-message-type 5;
  option domain-name-servers 192.168.0.1;
  option dhcp-server-identifier 192.168.0.1;
  option interface-mtu 576;
  option broadcast-address 255.255.255.255;
  renew 1 2009/03/09 01:20:12;
  rebind 1 2009/03/09 01:20:12;
  expire 1 2009/03/09 01:20:12;
}
lease {
  interface "eth0";
  fixed-address 192.168.0.11;
  option subnet-mask 255.255.255.128;
  option routers 192.168.0.1;
  option dhcp-lease-time 86400;
  option dhcp-option-overload 3;
  option dhcp-message-type 5;
  option domain-name-servers 192.168.0.1;
  option dhcp-server-identifier 192.168.0.1;
  option interface-mtu 576;
  option broadcast-address 255.255.255.255;
  renew 1 2009/03/09 12:17:13;
  rebind 1 2009/03/09 22:20:17;
  expire 2 2009/03/10 01:20:17;
}

[PasQty (pas-i)]

sorry but for sure:
ifconfig eth0
eth0 Link encap:Ethernet HWaddr 00:11:d8:a2:a2:49
          inet addr:192.168.0.10 Bcast:192.168.0.127 Mask:255.255.255.128
          UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
          RX packets:40662 errors:0 dropped:0 overruns:0 frame:0
          TX packets:25541 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:55877425 (55.8 MB) TX bytes:7549665 (7.5 MB)
          Interrupt:21 Base address:0x2000
obviously when i change the MTU in NetworkManager to automatic ifconfig eth0 looks like that
eth0 Link encap:Ethernet HWaddr 00:11:d8:a2:a2:49
          inet addr:192.168.0.10 Bcast:192.168.0.127 Mask:255.255.255.128
          UP BROADCAST RUNNING MULTICAST MTU:576 Metric:1
          RX packets:40662 errors:0 dropped:0 overruns:0 frame:0
          TX packets:25541 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:55877425 (55.8 MB) TX bytes:7549665 (7.5 MB)

/var/lib/dhcp3/dhclient.leases and /etc/network/interfaces is identical like over.
          Interrupt:21 Base address:0x2000

[PasQty (pas-i)]

https://bugs.launchpad.net/bugs/92567 seems the same.

[Brian Murray (brian-murray)]

This bug is likely a duplicate of bug 274069 however its really hard to tell since there isn't sufficient information. PasQty - what version of Ubuntu are you running and what package version of dhcp3 do you have installed? You can check via 'apt-cache policy dchp3-client'.

[PasQty (pas-i)]

user@host:~$ apt-cache policy dhcp3-client
dhcp3-client:
  Zainstalowana: 3.1.1-1ubuntu2
  Kandydująca: 3.1.1-1ubuntu2
linux version:
Ubuntu 8.10 intrepid for am64

i made some work-around. when card LAN is already up then networkmanager call scripts from /etc/network/if-up.d
so, in dir /etc/network/if-up.d add file setmtu1500
in setmtu1500 is:
#!/bin/bash
# set MTU = 1500
ifconfig eth0 mtu 1500

[PasQty (pas-i)]

 uname -a
Linux pasi 2.6.27-14-generic #1 SMP Fri Mar 13 19:54:51 UTC 2009 x86_64 GNU/Linux

[Bryan Quigley (bryanquigley)]

A number of fixes have landed in network manager since this and I believe it is fixed in the current version. If not, please do reopen.