[GTALUG] Rogers and MTU size

James Knott james.knott at rogers.com
Sun Jan 4 20:30:51 UTC 2015

On 01/04/2015 01:59 PM, Kevin Cozens wrote:
> On 15-01-04 12:55 PM, James Knott wrote:
>> One thing I noticed recently was that my firewall, running Linux, was
>> getting a MTU of 576 bytes, instead of the normal 1500 bytes.  This was
>> being set by the Rogers DHCP server (option 26).
> [snip]
>> I have advised Rogers of this and the person I was speaking to agreed it
>> should be 1500.  Let's see if they fix it.
> I am on Rogers and just checked my MTU setting after reading James'
> email. The ifconfig output reports an MTU of 1500. I didn't change any
> settings for DHCP. Rogers may have already fixed the problem.

I just tried some more testing with my notebook computer.  It uses the
KDE network manager and appears to ignore the DHCP MTU value.  However,
I can only ping with up to 1472 bytes when connected to the cable
modem.  I get the same when I tether to my smart phone (Rogers), but get
the full 1500 to a local computer on my network.  I do not use DHCP
option 26 on my DHCP server.  It also doesn't appear to be used when
tethered to my smart phone.

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