When we moved into the new house, we went to Telkom to get our ADSL connected. They insisted it would take several weeks and they had to have physical access to the property, even though the previous owners had only cancelled their account two weeks before we moved in. This caused us to storm out of the Telkom offices, vowing never to darken their doorsteps again and get iBurst instead. The sign-up process was efficient and I left the store 20 minutes later with their desktop modem and an antenna in case our reception wasn’t so good.
Installation was a breeze, and minutes later I was connected. However, the connection seemed erratic, with some sites loading faster than others and some strange freezing from time to time, even thought the iBurst speed tester reported really good speeds. I phoned support and they cleared it up for me: set the MTU to 1392 they said. No problem. Setting the MTU down made things work really well, but there was a slight snag. I had connected the iBurst device to our Time Capsule to access it wirelessly. Unfortunately, the Time Capsule is not capable of much in terms of routing. In router-speak, it is basically a bridge. The iBurst device is also a bridge, so the computer had to do the PPPoE dialing and the setting of the MTU. Things appeared fine until we tried to connect with our iPhones, which have no way of setting the MTU. So I fired up our little Netgear router and set it to do the PPPoE and the MTU, then chained the Time Capsule from that. Still no joy – turns out the Netgear WGR614 has a known issue with handling the MTU (we would later find out it wasn’t the Netgear’s fault as such, but read on).
For a long time (probably too long), we used the iBurst on our laptops, but had to use the data connections on our phones in our own house. Not good. When my father gave me a good price on his old iPad, with no 3G, it became really clear we had to do something. A friend at work suggested the MikroTik 750g as a really capable unit with lots of customisability. Some research showed that MikroTik has a huge community and that RouterOS surely had what I needed to get the problem sorted out.
Of course, with great power and flexibility comes great confusion to novice users, so it took me a couple of hours and several phone calls to friends to get the whole thing sorted out, but heres the lowdown:
My top tip is to do all the configuration up to step 3 before unplugging your working internet connection. The configuration can all be done with the box directly connected to a laptop and you don’t need to have it connected to the iBurst device during config.
Step 1: Update the firmware on the MikroTik – pretty simple, and allows much more to be done via the web interface. The web interface also has a copy of WinBox, which enables a vast array of configuration options.
Step 2: Configure PPPoE dialout. Go to PPP on the left hand menu in WinBox or Webfig, then do “Add new”/”PPPoE client” and configure the username and password. Also check the “Add default route” and “Use Peer DNS” options. You can set the MTU to 1392 here, but this is not all you need to do – keep reading. I recommend using the first ethernet connection for this, this is what they assume you’ll do anyway.
Step 3: Add a mangling rule to force lower MTU. Go to /IP/Firewall/Mangle – the PPPoE client setup should have added two rules to change the MSS. You’ll notice you can’t edit them, but copy the outgoing one and change the “New TCP MSS” to “clamp to pmtu”. Also make sure this new rule is above the old one in the rule table (you can drag them around to re-order them).
Step 4: Plug it in and check that everything works. You can use WinBox to check that the PPPoE is working and that the mangling rule for clamping is getting the traffic before the other one. That’s it. Hopefully this will save other people the hassle I had to go through.
Leave a Reply