Cisco Systems Pix & large ping packets

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Subject Author Date
Pix & large ping packets Christoph Gartmann 05-03-07
Posted by Christoph Gartmann on May 3, 2007, 9:58 am
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Hello,

the largest ping packet that is able to go through our PIX515 (software
version 7.2(2)) is 992 bytes. Larger packets are dropped. MTU size is 1500
and we have a statement "sysopt connection tcpmss 1460". What is necessary
to increase the possible packet size for a ping?

Regards,
   Christoph Gartmann

--
 Max-Planck-Institut fuer      Phone   : +49-761-5108-464   Fax: -452
 Immunbiologie
 Postfach 1169                 Internet: gartmann@immunbio dot mpg dot de
 D-79011  Freiburg, Germany
               http://www.immunbio.mpg.de/home/menue.html

Posted by Walter Roberson on May 3, 2007, 8:35 pm
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The 1000 byte icmp packet limitation was introduced in 6.3, which
offered no way to adjust the maximum.

Are you getting IDS 2151 (message 400024) generated, "Large ICMP" ?
The documentation for that indicates the limit is 1024 bytes including
IP headers.

You could -try- disabling inspect icmp, but I don't know if
that will work.

I've searched through the 7.2 command reference, but do not see
any adjustment method documented.

Posted by Christoph Gartmann on May 4, 2007, 3:20 am
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Roberson) writes:

Ah, I see.


I didn't look further into it. I simply realized the limit of 992 bytes.


It doesn't :-(

Regards,
   Christoph Gartmann

--
 Max-Planck-Institut fuer      Phone   : +49-761-5108-464   Fax: -452
 Immunbiologie
 Postfach 1169                 Internet: gartmann@immunbio dot mpg dot de
 D-79011  Freiburg, Germany
               http://www.immunbio.mpg.de/home/menue.html

Posted by Sam Wilson on May 4, 2007, 4:57 am
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 roberson@hushmail.com (Walter Roberson) wrote:


FWSM 3.1(3) seems to OK - my colleague has just verified that we can get
7.5K pings to a host through ours, though 9K doesn't work.  We don't
know if that's a feature of the host we're testing rather than the FWSM.

Sam

Posted by Christoph Gartmann on May 4, 2007, 9:32 am
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Now I found the following command:
   ip audit signature 2151 disable
This command is available in software version 7.x. Now the limit is at 1472
bytes. Now the question is where this one comes from ...

Regards,
   Christoph Gartmann

--
 Max-Planck-Institut fuer      Phone   : +49-761-5108-464   Fax: -452
 Immunbiologie
 Postfach 1169                 Internet: gartmann@immunbio dot mpg dot de
 D-79011  Freiburg, Germany
               http://www.immunbio.mpg.de/home/menue.html

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