DSL (iBurst) bonding options

So recently I started getting a lot of inquiries about ADSL line bonding and decided it was time to start investigating. Various options have presented itself, but very few true solutions.

The normal approach to the problem is to just use mutli-link ppp. Unfortunately none of the Telco’s that I’m interested in (Telkom / iBurst) supports multilink on their LNS/NAS infrastructure, so basically we’re stuck with multiple individual pppoe connections.

ULS has long been performing load balancing along with split routing (separation of local and international traffic) of up to four ADSL lines using Mikrotik, and an arbitrary (we’ve done up to 9) number of DSL lines on a Linux router and VLAN switch.

The requirement for actually running single flows at >10Mbps requires that the links be properly bonded. This gives us a few basic things we’ve got to work with:

* Individual PPPoE links from the premises to the telco.
* We will need to establish an IP-layer tunnel between the client-perimeter-equipment (CPE) and a point on the internet (LNS).

At this point we have a few potential hacks. There are various tunneling protocols, some are raw ethernet, others are more involved, like pptp which runs a ppp link over a GRE tunnel, or simply l2tp which encapsulates layer2 frames inside udp.

Not surprisingly, the Linux network stack separates out the tunneling from the ppp, so it just so happens that it’s possible to run multilink ppp on top of whatever layer2 tunneling is in use (ethernet/eoip, gre or l2tp – of which I’ve set up all three options today). Seeing that we can integrate this with radius the benefits are numerous.

The question really becomes what CPE equipment can we use to utilize this, without having to set up and maintain full-blown Linux systems. Ideally we want a relatively low power device, single device with multiple DSL ports, and preferably four ethernet ports, but a single one will do.

As it turns out, there exists a CPE that will suffice. CISCO produces a very comprehensive set of routers, and all of their routers have the software functionality, but only on their higher end (2900 series routers) is it possible to have 4 DSL ports by method of expansion slots. Sounds like the 1800 series routers should be able to get to 3 DSL ports, and a significant price reduction. Either way, for those in the loop, CISCO is expensive.

Mikrotik is another very popular mid-range router, but doesn’t have DSL functionality. Not a major issue, get a number of single-port DSL modems, they’re not overly expensive but now you are starting to get into a situation where you end up with a LOT of cabling and potential problems. The other problem is that Mikrotik only truely supports multilink ppp using pppoe, so we end up with an additional layer, first we need to establish a number of pppoe connections for the ADSL, then we need to create Ethernet-over-IP tunnels on top of which we can then create a multilinked pppoe connection. Ethernet-over-IP is a pain unless you have static IPs on both ends, fortunately the author of linux-eoip (http://code.google.com/p/linux-eoip/) assisted me today to at least improve the situation somewhat.

After a very long discussion and a lot of back and forth with Peplink today they too admitted they can’t help on this particular requirement. Although I must say their devices are (at least from the specifications) very impressive.

Billion apparently has some multi-port DSL modems, although I haven’t yet managed to get hold of one, nor could I make contact with their distributors in South Africa yet, or even get hold of a model number.

Then there is the Fishbone routers. Which is also hard to get information on.

Then the last, and probably the route ULS will go with, permitting we can get the required firmware running, is to re-flash the MT RB750 with the OpenWRT distro and to revert to using multilink ppp/l2tp. It’s really odd that Mikrotik is refusing to add multilink ppp/l2tp support to RouterOS. This will allow us to truely bond up to four ADSL lines, and with larger MT boards (eg, the RB1100 or RB1200) it may be possible to do even more.

Along with the bonding of the DSL lines there are a few other advantages for the solution.

We can now provide clients with static IPs on their ADSL links, same as Internet Solution’s business DSL. Other ISPs already have similar solutions, but most of the static-IP solutions are utilizing a single ADSL line. Be it a single static IP going to the router, on which port-forwarding can then be set up, or IP block, which we can then route to the client’s LAN, where he can assign the block as he sees fit.

Watch this space. Coming VERY soon.

One Response to “DSL (iBurst) bonding options”

  1. Moon says:

    Hello nice article but what will be the result in the end is there any hope
    to get Bonded DSL lines, now in these days many bonding adsl routers available cheap and expensive, I hope one day I will use adsl bonding by Linux .

    Thanks Keep IT up