DHCP option 26 (MTU)

[Carl Williams]

Hi All,


  I have set the DHCP Client to request option 26 and configured an ISC
DHCP server to respond with DHCP 26 with specified MTU.

  I used a MAC OS version 10.6.4 and added option 26 to the default list
for dhcp client to request in the file:
/System/Library/SystemConfiguration/IPConfiguration.bundle/Contents/Resourc
es/IPConfiguration.xml


   My MACBOOK Air (Lion) has no such file and I can't figure out how to do
it on the Lion OS.

   But on the MACOS 10.6.4 I can see from the wireshark files that option
26 with the MTU that I set in server is in fact
Being sent via DHCP OFFER and DHCP ACK.  But the interface that DHCP is
configured on - en0 - is not setting the MTU as specified according
To the DHCP response.


   I am wondering what OS have what behavior and handle this option.  This
is not so clear.

   I also want information on how to set this on Windows 7 or some version
of windows - the registry setup is complicated and I tried it
But no MTU request (option 26) is being made by the windows box despite me
setting up a registry key for option 26 for dhcp.  Perhaps I need
To trigger it some how or do some extra stuff there - not sure.

  But also any other information on dhcp option 26 on any os would be
useful.

Carl


On 11/2/11 7:32 AM, "Ralph Droms" <rdroms at cisco.com> wrote:

>I would be interested to hear if receiving DHCP option 26 has an effect
>on the interface MTU; i.e., are there any clients that actually process
>DHCP option 26 and make the appropriate change to the interface settings
>through the client OS.
>
>- Ralph
>
>On Nov 1, 2011, at 4:00 PM 11/1/11, Carl Williams wrote:
>
>> 
>> 
>> I wish to have my MACOS (Macbook Air) request the DHCP option 26 for
>>setting MTU.  How can I change the default MACOS (LION) dhcp options to
>>do this?
>> 
>> Also if you have same to add this option 26 to windows 7 as well?
>> 
>> Carl
>> 
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