Hi all,
Thought I'd share with you the solution to networking issues that were totally ruining my experience of the Vigor 120 PPPoA/PPPoE translation.
I connected my Vigor 120 to the wall and then used a DD-WRT flashed Buffalo router to handle DHCP, NAT, acting as the PPPoE client.
I found that whilst I could do most things, I was experiencing problems on my iPhone checking for updates on the App Store app, streaming YouTube videos or logging in to any of my Zynga games (e.g. Mafia Wars). Basically I could do none of these things, they all just timed out.
Through the process of elimination, I managed to rule out the DD-WRT, which left only the Vigor 120 as the culprit.
Needless to say at this point I was really cussing down DrayTek and wondering if I'd wasted my money.
One day I woke up, dusted off my Networking Geek hat, determined to fix this problem. And it paid off.
The problem, I discovered, revolves around MSS (Max Segment Size). Max segment size is basically the payload that the packet is capable of carrying after the tcp headers have been used. I reasoned that the PPPoE / PPPoA translation was shielding the router from correct MSS negotiation with the modem. As a result, where the PPPoE headers were munching another 8 bytes of space on the WAN side, some payloads from LAN clients going out to the internet were too big now to fit and were therefore timing out.
The solution then was simple: reduce the size of the available payload space for NAT traffic. I manually set the MTU (which I reasoned must be being clamped to the MSS by DD-WRT, and is something you can do in any PPPoE implementation e.g. in the Linux kernel), to 1412, leaving bags of room for headers in the rest of the usual c. 1500 byte packet.
This worked! Now everything can communicate from the LAN across the Vigor 120 and out to the WAN without any problems.
This was really doing my head in, so I thought I would share with the rest of you in case it stops someone else from going mental.
Owen Gerrard
http://twitter.com/ogerrard
