# Unsure of error message.

**URL:** <https://community.cambiumnetworks.com/t/unsure-of-error-message/46441>\
**Category:** ePMP\
**Created:** [July 15, 2016, 2:51pm UTC](https://community.cambiumnetworks.com/t/unsure-of-error-message/46441 "2016-07-15T14:51:28Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![LothianB](https://d10gw3vjmzyp8.cloudfront.net/letter_avatar_proxy/v4/letter/l/2bfe46/32.png) [@LothianB](https://community.cambiumnetworks.com/u/LothianB)\
**Post date:** [July 15, 2016, 2:51pm UTC](https://community.cambiumnetworks.com/t/unsure-of-error-message/46441/1 "2016-07-15T14:51:28Z")

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We have had a number of subscriber modules&nbsp;dissociating with an access point on firmware 2.6.2.1 RC4 and cant seem to see a reason as to why they are doing so. (epmp 1000s)

We have also noticed one of the subscriber modules&nbsp;reporting an error in the logs:

xt\_TCPMSS: bad length (1386 bytes)&nbsp;

xt\_TCPMSS: bad length (1386 bytes)&nbsp;

xt\_TCPMSS: bad length (1386 bytes)&nbsp;

xt\_TCPMSS: bad length (1386 bytes)&nbsp;

The subscriber modules have recently been replaced to F180's with firmware 2.6.2.1 RC4 as we had to do something to try and sort the customers and these are currently&nbsp;being monitored.

If any one knows any reason as to what this error message may be that would be helpful.

Thanks&nbsp;

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**Author:** ![Fedor](https://d10gw3vjmzyp8.cloudfront.net/user_avatar/community.cambiumnetworks.com/fedor/32/20305_2.png) [@Fedor](https://community.cambiumnetworks.com/u/Fedor)\
**Post date:** [July 18, 2016, 7:35am UTC](https://community.cambiumnetworks.com/t/unsure-of-error-message/46441/2 "2016-07-18T07:35:20Z")

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Hi LothianB,

Error message indicates that packet with bad MTU size is detected and cannot be handled.

Please check your MTU setting on SM and Devices which are interacting with it.

It is not related to SM's disassociation events.

Please enable and then check System log on AP and SM whether disassociation reasons was written.

Please find list of reasons in Knowledge Base:

[http://community.cambiumnetworks.com/t5/ePMP-Troubleshooting/Network-Entry-State-Definitions-and-Courses-of-Action/m-p/40712#U40712](https://community.cambiumnetworks.com/t/network-entry-state-definitions-and-courses-of-action/40551)

Thank you.

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**Author:** ![LothianB](https://d10gw3vjmzyp8.cloudfront.net/letter_avatar_proxy/v4/letter/l/2bfe46/32.png) [@LothianB](https://community.cambiumnetworks.com/u/LothianB)\
**Post date:** [July 18, 2016, 10:08am UTC](https://community.cambiumnetworks.com/t/unsure-of-error-message/46441/3 "2016-07-18T10:08:23Z")

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Thanks for the reply,

We've not changed any of the MTU setting on any of the units away from the default

LB

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<div class="post-metadata">

**Author:** ![Fedor](https://d10gw3vjmzyp8.cloudfront.net/user_avatar/community.cambiumnetworks.com/fedor/32/20305_2.png) [@Fedor](https://community.cambiumnetworks.com/u/Fedor)\
**Post date:** [July 18, 2016, 10:30am UTC](https://community.cambiumnetworks.com/t/unsure-of-error-message/46441/4 "2016-07-18T10:30:54Z")

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in that case it means that someone trying to send TCP traffic with not supported MTU size through SM.

Thank you.

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<div class="post-metadata">

**Author:** ![LothianB](https://d10gw3vjmzyp8.cloudfront.net/letter_avatar_proxy/v4/letter/l/2bfe46/32.png) [@LothianB](https://community.cambiumnetworks.com/u/LothianB)\
**Post date:** [July 18, 2016, 10:32am UTC](https://community.cambiumnetworks.com/t/unsure-of-error-message/46441/5 "2016-07-18T10:32:43Z")

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That's kind of what we thought. &nbsp;We'll watch this for a while longer...

Thanks