On 16/04/14 21:07, Keith Owens wrote:
> On 16/04/14 12:24, Toby Corkindale wrote:
>> Hi,
>> I posted last year about a problem I was having with Linux's PPPoE
>> functionality in regards to a specific modem. At the time I put it
>> down to a dodgy modem and moved on, but now I've hit it on another
>> modem, and twice seems more than coincidence.
>>
>> The problem is that path MTU detection seem to break when the "bad"
>> modems are involved. So the Linux box running pppoe is OK, because it
>> knows the interface has an mtu+mru of 1492, but masqueraded clients do
>> not.
>> You can work around the problem a bit, by having an iptables rule with
>> --clamp-mss-to-pmtu, but it's a kludge.. and importantly, only
>> required for two of these four modems. The other two work just fine
>> *with apparently identical configurations* (ie. LLC / bridged)
>>
>> Can anyone think of a reason for this?
>>
> Wild guess - segmentation offload. I have seen offload do really strange
> things with masqueraded packets and it is just possible that the bad
> modems support offload but the good modems do not. On the linux box, issue
>
> for interface in eth0
> do
> for option in tso ufo gso gro lro
> do
> ethtool $interface $option off
> done
> done
>
> Replace eth0 with all the physical network interface names (eth0 eth1 etc.).
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<idiot>
for interface in eth0
do
for option in tso ufo gso gro lro
do
ethtool -K $interface $option off
done
done
</idiot>
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