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What does this error mean: "user.err kernel: ipt_tcpmss_target: bad length (48 bytes)"

Discussion in 'Tomato Firmware' started by Cynsick, Jan 1, 2013.

  1. Cynsick

    Cynsick Addicted to LI Member

    So I got another first time error in my logs again. Anyone shed some light? I know about MTU and MSS, MTU is 1492, using DSL. What would cause the following, it hasn't happened again since. I tried an internet search and found some old thread someone thinking they were getting hacked, but it didn't seem like the person knew what they were talking about.

    Dec 30 11:01:46 unknown user.err kernel: ipt_tcpmss_target: bad length (56 bytes)
    Dec 30 11:01:49 unknown user.err kernel: ipt_tcpmss_target: bad length (1492 bytes)
    Dec 30 11:01:51 unknown user.err kernel: ipt_tcpmss_target: bad length (1492 bytes)
    Dec 30 11:01:55 unknown user.err kernel: ipt_tcpmss_target: bad length (1492 bytes)
    Dec 30 11:01:58 unknown user.err kernel: ipt_tcpmss_target: bad length (1492 bytes)
    Dec 30 12:00:01 unknown cron.info crond[5698]: crond: USER root pid 2403 cmd logger -p syslog.info -- -- MARK --
    Dec 30 12:00:01 unknown syslog.info root: -- MARK --
    Dec 30 12:27:06 unknown user.err kernel: ipt_tcpmss_target: bad length (48 bytes)
    Dec 30 12:27:17 unknown user.err kernel: ipt_tcpmss_target: bad length (48 bytes)
    Dec 30 12:27:33 unknown user.err kernel: ipt_tcpmss_target: bad length (48 bytes)
    Dec 30 12:27:38 unknown user.err kernel: ipt_tcpmss_target: bad length (48 bytes)
    Dec 30 12:27:41 unknown user.err kernel: ipt_tcpmss_target: bad length (48 bytes)
     
  2. koitsu

    koitsu Network Guru Member

    Search Google for the string "ipt_tcpmss_target: bad length" and you will find the answer. Be aware it is highly technical and requires great familiarity with TCP.
     
  3. Cynsick

    Cynsick Addicted to LI Member

    Yeah those links are the ones I had found when I searched, just didn't seem to tell me enough as to why it just happened.
     
  4. koitsu

    koitsu Network Guru Member

    The top hit explains why/when (like I said, it's highly technical), meaning what the condition is that triggers the message: http://lists.netfilter.org/pipermail/netfilter/2003-August/046096.html

    There are an almost infinite amount of reasons this could be happening, and troubleshooting them all would take a very large amount of time + require a very high amount of technical expertise located physically at the site of the router.
     

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