ipt_tcpmss_target: bad length

ipt_tcpmss_target: bad length

[Laurens van Alphen]

Hello all,

Today, I received this kernel log entry via e-mail:

Aug 17 14:19:17 filter0 kernel: ipt_tcpmss_target: bad length (472
bytes)

Using Google, I could not find a single useful meaning of this message.

Anyone?

Thanks in advance!

--
Laurens van Alphen
Keen on dots

Re: ipt_tcpmss_target: bad length

[Philip Craig]

Laurens van Alphen wrote:
> Today, I received this kernel log entry via e-mail:
> 
> Aug 17 14:19:17 filter0 kernel: ipt_tcpmss_target: bad length (472
> bytes)
> 
> Using Google, I could not find a single useful meaning of this message.

Here's the comment from the source code which explains it:

/* Since it passed flags test in tcp match, we know it is is
    not a fragment, and has data >= tcp header length.  SYN
    packets should not contain data: if they did, then we risk
    running over MTU, sending Frag Needed and breaking things
    badly. --RR */

In other words, SYN packets cannot have data, so the total length
of the packet must be the same as the tcp header length, otherwise
it is a bad length.

-- 
Philip Craig - philipc@snapgear.com - http://www.SnapGear.com
SnapGear - Custom Embedded Solutions and Security Appliances