I'm asking again, for some reason, does this happen with every browser on every operating system? The reason I ask is that if it's OK on, *for example*, Chrome on Windows I would suggest it *most likely* has less to do with networking and more to do with something on the host layer. It would be very interesting if it does happen with other combinations, not so much if it's just one. On 16/03/13 18:08, James Harper wrote:
Packet loss? -- I can't tell for sure. There are definitely some packets being dropped as seen from SACK packets, but that's expected with inbound policing, and the missing packets are resent in a timely fashion.
I'd have to capture quite a lot of packets to see the problem though so I haven't been able to analyse it properly at this time.
I've been monitoring this a bit more and have noticed that the freeze's appear to coincide with the appearance of incorrect checksums on outbound packets on the ppp link, which in turn also appear to have SACK options attached.
Unless the router (buffalo running openwrt) has building in pppoe checksum offloading, I think I should never see packets with incorrect checksums, so I may be on to something.
I'm now simultaneously monitoring both the wlan (where my laptop is) and eth0.2 (pppoe packets go here) in the hope of seeing such a packet coming from my laptop and going out with the bad checksum, but nothing yet.
I'm vaguely suspicious that this is a heisenbug. The only time I've seen it is when I've caught it in the middle of a loop like: Here's an ack/sack packet with a bad checksum Hmmm... you didn't get it... here's the same ack/sack packet with a bad checksum
I've never seen the above situation develop while I've been monitoring it, only when I start monitoring when it's already developed.
OS is Openwrt AA 12.09-rc1 running 3.3.8 kernel.
The other alternative is that tcpdump is calculating checksums incorrectly and the actual checksums are fine and the bug is somewhere else.
James
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