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.).