I have this IPv6 issue with my ADSL. It's kinda bizarre and I'd be interested in whether anyone has any ideas or has seen anything similar themselves.
I don't get IPv6 packets smaller than 71 bytes (excluding the PPP header).
Small IPv4 packets? No problem. Sending small IPv6 packets? Also fine. Getting them back again? No go.
I first noticed the problem because I couldn't get to Google's IPv6 site. I ended up getting some quite useful help from various Google engineers, who were prepared to take my report seriously even though I'm just an end user these days. I've promised to get back to them with what the problem was when I find out. If.
My ADSL is provided by Enta, through a reseller. My parents also use them, but via a different reseller. My understanding is this shouldn't make a difference, as Enta are responsible for terminating the connection in both cases. On my parents' line IPv6 seems to work fine. They have a Linux box with a Conexant based PCI card. I have an AR7 router running OpenWRT. My first thought was that it might be some weird hardware issue, so I dug out my Speedtouch, hooked it up to my laptop and tried that. Still no small packets. I tried a different AR7 ADSL router. I downgraded to a 2.6.16.x kernel (which is what my parents are on). All gave the same results; anything over 70 bytes would get through fine, anything under wouldn't.
So I took my router to my parents'. I unplugged their kit and plugged the router in, with only my laptop attached. I left it configured with my username/password. And it worked. Small packets came though fine. To make absolutely certain I tried the same thing again at home. And it didn't work.
Now. Exactly the same kit at my end in both instances. Exactly the same ISP at the other end (who confirm all their end points are configured identically and even if they're not I'd have expected to get a duff one at my parent's once or twice and a working one at my end given the number of reconnections I've made over the period of trying this all out). That leaves BT as the variable (we're about 100 miles apart, so very different exchanges).
My questions to you, the reader:
- Does this line of logic seem reasonable? If not, what have I missed?
- Have you ever heard of anything similar? I know BT used to have an issue with IPv6 and PPPoE and corruption of the packet length field, but I'm using PPPoA (I've tried PPPoE as well and it wasn't any better).
- Is there an ATM packet sniffer for Linux, along the lines of Wireshark? If I could hook up the Speedtouch to my laptop and try a connection while sniffing the ATM packets I could see if there was any corruption or oddities happening at that level, which might provide a clue.
Update: will-h has pointed out it's 70 bytes excluding the PPP header, not including it.