On Feb 25, 2012, at 8:09 PM, Bruce Dubbs wrote:
> Qrux wrote:
>
>>> if test -n "${MTU}"; then
>>> if [[ ${MTU} =~ ^[0-9]+$ ]] -a [[ $MTU -ge 68 ]] ; then
>>> ip link set dev ${IFACE} mtu $MTU
>>> else
>>> echo "Invalid MTU $MTU"
>>> fi
>>> fi
>>
>> Yeah, that looks good. Is 68 some absolute kernel minimum? Does
>> that consider stuff like SLIP, PPP, ATM, FDDI, IP-over-IEEE-1394,
>> etc?
>
> It's the IPv4 minimum. See RFC 791. All the others are quite a bit
> higher. A better practical minimum is probably 576.
>
> That's all theory stuff. I've never seen an actual need to change the
> default MTU, but I've played with it.
>
> http://en.wikipedia.org/wiki/Maximum_transmission_unit
Practically, I've had to change to a lower one for PPP connections, and higher
ones for better gigE throughput. Some people have modems; others have machines
in a data center.
I don't think it's about the applicability of the setting. MTU needs to be
allowed in the config file. As such, I don't think we should unnecessarily
restrict it, other than values which cannot possibly work (non-positive
integers).
Q
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