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Thread: Help! New to Ubuntu, eth0 doing my nut!

  1. #21
    Join Date
    Aug 2008
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    Re: Help! New to Ubuntu, eth0 doing my nut!

    Oh yes. It means that packets smaller than 1500 bytes (what your MTU is set at) but larger than 1492 bytes just get lost in the network.

    type
    Code:
    ifconfig | grep MTU
    sudo ifconfig mtu 1492
    ifconfig | grep MTU
    And then try surfing...

    Also post output from
    Code:
    cat /etc/network/interfaces

  2. #22
    Join Date
    Jan 2010
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    19

    Re: Help! New to Ubuntu, eth0 doing my nut!

    ifconfig | grep MTU
    UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
    UP LOOPBACK RUNNING MTU:16436 Metric:

    sudo ifconfig mtu 1492
    SIOCSIFADDR: No such device
    mtu: ERROR while getting interface flags: No such device

    cat /etc/network/interfaces
    auto lo
    iface lo inet loopback

  3. #23
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    Aug 2008
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    Re: Help! New to Ubuntu, eth0 doing my nut!

    Hm. Try
    Code:
    sudo ifconfig eth0 mtu 1492
    ifconfig | grep MTU
    And then try surfing...

  4. #24
    Join Date
    Jan 2010
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    19

    Re: Help! New to Ubuntu, eth0 doing my nut!

    udo ifconfig eth0 mtu 1492
    [sudo] password for dan:
    dan@dan-desktop:~$ ifconfig | grep MTU
    UP BROADCAST RUNNING MULTICAST MTU:1492 Metric:1
    UP LOOPBACK RUNNING MTU:16436 Metric:1


    Yes! That worked. Fantastic.

    So.... is that a permanent fix? Or more tweaking required?

  5. #25
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    Aug 2008
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    Re: Help! New to Ubuntu, eth0 doing my nut!

    Can you now surf uninterruptedly?

    Apparently that's not a permanent fix. I haven't done this, but it looks like if you right-click the network icon on the panel and select Edit connections... then make sure you are on the wired tab and select Auto eth0 and click Edit ... you should have an MTU box which probably says 'automatic'. Type 1492 in that box.

  6. #26
    Join Date
    Jan 2010
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    19

    Re: Help! New to Ubuntu, eth0 doing my nut!

    Have done that. The profile in the network box is 'Wired Connection 1' - no sign of 'Auto Eth0' these days.

    Seem to be able to surf uninterruptedly. Hang on, will just reboot to check if the machine has now learned it's lesson or if it's just toying with me....

  7. #27
    Join Date
    Jan 2010
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    19

    Re: Help! New to Ubuntu, eth0 doing my nut!

    Yes! Fantastic! I can now get on with some work...

    Many many thanks people. I wouldn't have had the first clue how to start figuring that out.

    One more question - I usually switch the router off when we're not using computers, to save energy, cos I hate the thought of power stations rumbling away out there in the distance, pumping crap into the atmosphere just to power devices that aren't being used. I'm sure 10 years from now the whole idea of standby will seem like a weird anomaly. Anyway... my brother tells me that regularly switching off a router is a bad idea. Always seems to work fine, but what do you learned people think?

  8. #28
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    Aug 2008
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    Re: Help! New to Ubuntu, eth0 doing my nut!

    I leave my router and firewall on all the time ... partly because I never know when other members of the family might get up early and want to use the net.

    With most electronic devices, the power-off power-on cycle does reduce their lifetime a bit. But I don't know if that's a serious consideration: routers tend to be fried by lightning strikes or to mysteriously die 2 weeks after the warranty expires.

    More seriously, the power required to restart it could be more than the power consumed by being left on overnight. You could get a power consumption meter and test it. If it's less than 1W then it's fine. (Even TVs and DVD players in standby typically use more than this, although new guidelines require less.) My router uses about 4W.

  9. #29
    Join Date
    Jan 2006
    Location
    Not heaven... Iowa
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    Distro
    Ubuntu

    Re: Help! New to Ubuntu, eth0 doing my nut!

    =D> Congrats on winning (at least for now) a hard-fought battle. I'm gonna reference this thread for other likely MTU-villain analysis. In the meantime - if you think the villain is captured, and the problem fixed, this should help you mark the thread [SOLVED].
    Linux User #415691 Ubuntu User #8629
    Iowa Team (LoCo): [Wiki] [Launchpad]
    IRC channel: #ubuntu-us-ia on irc.freenode.net

  10. #30
    Join Date
    Jun 2006
    Location
    Rockville, MD
    Beans
    29
    Distro
    Ubuntu 12.10 Quantal Quetzal

    Re: Help! New to Ubuntu, eth0 doing my nut!

    I'm having, I think, the same problem. Unfortunately, I can't seem to figure out the magic number for my MTU.

    It defaults to 1500.
    Here's a couple outputs from my pings to my router:
    Code:
    ping 192.168.75.1 -c 1 -s 1480 -M do
    PING 192.168.75.1 (192.168.75.1) 1480(1508) bytes of data.
    From 192.168.75.51 icmp_seq=1 Frag needed and DF set (mtu = 1500)
    
    --- 192.168.75.1 ping statistics ---
    0 packets transmitted, 0 received, +1 errors
    Code:
    ping 192.168.75.1 -c 1 -s 1472 -M do
    PING 192.168.75.1 (192.168.75.1) 1472(1500) bytes of data.
    1480 bytes from 192.168.75.1: icmp_seq=1 ttl=127 time=0.948 ms
    
    --- 192.168.75.1 ping statistics ---
    1 packets transmitted, 1 received, 0% packet loss, time 0ms
    rtt min/avg/max/mdev = 0.948/0.948/0.948/0.000 ms
    1472 is the highest I can do it without an error.

    Strange thing about my problem. I've got my laptop working connected wirelessly, but my desktop is the one that isn't working, and it's using a wired connection to the same router.

    Both computers are running 10.04.

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