Comments on: How to Change MTU (Maximum Transmission Unit) of network interface in Ubuntu Linux

By: mark

mark — Thu, 15 Sep 2011 21:54:27 +0000

ok so im trying to get on xbox live and its telling me i need to change the mtu i have no idea how to do so can someone help me out with step by step directions
plz

By: Neel

Neel — Fri, 11 Mar 2011 04:32:14 +0000

Evolution mail, youtube-dl, PUBKEY and many more such tools aren’t working on my ubuntu 10.10, however my browser opens all the websites very normally. Can it be a problem with the MTU??
I ran the command sudo ifconfig -a on the terminal and the output is as follows:

eth0 Link encap:Ethernet HWaddr d8:d3:85:30:cf:33
inet addr:192.168.1.4 Bcast:192.168.1.255 Mask:255.255.255.0
inet6 addr: fe80::dad3:85ff:fe30:cf33/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:960 errors:0 dropped:0 overruns:0 frame:0
TX packets:783 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:1005736 (1.0 MB) TX bytes:90389 (90.3 KB)
Interrupt:45 Base address:0xc000

lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:4 errors:0 dropped:0 overruns:0 frame:0
TX packets:4 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:240 (240.0 B) TX bytes:240 (240.0 B)

pimreg Link encap:UNSPEC HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00
UP RUNNING NOARP MTU:1472 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)

wlan0 Link encap:Ethernet HWaddr 70:f1:a1:55:b3:d4
inet addr:192.168.1.2 Bcast:192.168.1.255 Mask:255.255.255.0
inet6 addr: fe80::72f1:a1ff:fe55:b3d4/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:6 errors:0 dropped:0 overruns:0 frame:0
TX packets:35 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:980 (980.0 B) TX bytes:6398 (6.3 KB)
Interrupt:17 Memory:f87e0000-f87e0100.

Please suggest appropriate changes.

By: jonny rocket

jonny rocket — Mon, 14 Feb 2011 18:00:07 +0000

BUT, what should it be set too?

By: jk

jk — Mon, 19 Jul 2010 03:56:28 +0000

To find out MTU you can do a ping to any destination, set the DF bit to 1 (Dont Fragment) and play around with the packet size until you find a limit that works.

To do this in ubuntu:
ping -Mdo -s 1500 8.8.8.8

-Mdo sets DF to 1
- s 1500 sets your buffer to 1500 bytes
- 8.8.8.8 is a destination IP

The above command should return that the packet cant be fragmented or the message is too long (or similar). You then reduce the size of the packet (eg. -s 1490) until you get a reply. Then increase and reduce the number until you find the exact MTU you should use.

By: Steve

Steve — Wed, 11 Feb 2009 23:28:02 +0000

I can’t get ‘mtu size’ to work for eth0 when it has a dynamic IP address. The manual for interfaces describes the ‘mtu size’ option for static IP addresses, as are used above. I’m running Ubuntu 8.04 LTS server.

Is this a bug ?

By: shirish

shirish — Sat, 17 Jan 2009 04:21:07 +0000

Hi all,
It seems tracepath does give what is suitable.

$ tracepath 74.126.24.86
1: Mugglewille-desktop.local (192.168.1.3) 0.355ms pmtu 1500
1: no reply
2: no reply
3: no reply
4: no reply
5: no reply
6: no reply
7: no reply
8: no reply
9: no reply
^C

So seems it is saying the best mtu is 1500

By: Arup Roy Chowdhury

Arup Roy Chowdhury — Fri, 14 Nov 2008 15:22:32 +0000

With Intrepid, the network manager has a tab for MTU setting and does it well, whoever thought about this, my hats off to him for incorporating this nifty feature.

By: Kyle Ragln

Kyle Ragln — Mon, 18 Aug 2008 16:31:27 +0000

The MTU becomes more important for people using Gigabit Ethernet. To get the best throughput (and if your switch supports it), it’s best to use “Jumbo” frames. Jumbo frames are enabled with an MTU of around 9000. Not all Gigabit Ethernet NICs support an MTU of 9000. As an example, my Realtek 8169 based card supports a maximum of 7200. Even at only 7200, transferring files between the computers on my LAN happens much faster than when using the default MTU of 1500. Of course, it’s best to check and see what the manufacturer suggests as the maximum supported MTU for the particular NIC you’re using.

By: Marco

Marco — Thu, 14 Aug 2008 21:49:56 +0000

Use the command tracepath to know the suitable MTU of your network

By: jj

jj — Thu, 14 Aug 2008 03:59:49 +0000

from what I found on http://www.debianadmin.org after Googling, settings for a static (not necessarily a dynamic [DHCP])address should be:

dialup 576
DSL 1492
cable modem 1500
fiber 4352

By: Peter

Peter — Wed, 13 Aug 2008 05:52:48 +0000

Well ok fine … that tells you how to change the MTU.

But what it does not tell you is how to find out whether you need to change your settings to 1300 or 1600 or whatever….. it cannot be simply trial and error. I hope.

1492 or 1500 seem to be the common defaults but there is never an explanation of what they could / should be …