Re: eql = tun + eth0
On Wed, Jan 16, 2002 at 08:58:32AM +0700, Oki DZ wrote:
> On Tue, 15 Jan 2002 crispin@iinet.net.au wrote:
> > Recently I gave eql a try to spread load across two links that I
> > controlled both ends of. I had lots of problems and I believe eql has
> > not been actively maintained in the kernel for a long time. The
> > enslaving of links works for outbound, but not for inbound traffic. I
> > was able to use the /proc/.../rp_filter set to 0 to allow the
> > backtraffic through, but it was in no way 'balanced'. >
>
> But my problem is how to split traffic to the Internet via two devices.
> The first one, eth0 is a wireless device, the second one tunl0 is a
> IP tunnel (which I have to set up yet) via a ppp0 device on another
> machine (the ppp0 connects to an ISP).
>
> The main idea is how to add more bandwidth to that eth0 using the modem,
> but I don't want to have a lot of editing on the firewall/NAT scripts
> (that are already on the machine which has the eth0).
The problem is that the eth0 and ppp0 (and thus tunl0) have different IP numbers and look to the routing infrastructure of the internet like two different computers. A packet leaving your site will have to choose one of them as its source IP. The return packets for that connection will have their dest IP set to that source IP and will be routed through the net accordingly to either your eth0 or ppp0. They wont be split between the two.
In TCP/IP we only have control of our outgoing traffic. Thus your connections will be set up via one or the other. Say your wireless device is 128k and your modem is 56k. With this sort of primative balancing you initiate a download. It comes down at 56k. It doesn't get any faster. Then you start another. It comes in at 128K with the first still going at 56K. You will *never* get a 184K download. Each connection is identified by its source and dest ip's and your IP's are different.
If you control both ends of the link then you can achieve the 184K, by re-bundling the connection on the other side. So then both links end in the same IP's on the same machine at the ISP.
There are other ways of doing this but your ISP has to co-operate. OSPF equal cost multipath is one way (but the links must be similar speed) and full BGP4 is another (but you'll need an ASN and its a crazy amount of work.)
Kind Regards
Crispin
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