-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1
Billy Crook wrote: | For a number of technical reasons, it is not possible to use two | residential internet connections to "accelerate" the path between the | same two computers. At least when using TCP, a persistent connection | has to originate from an IP address. Each of the dsl modems will be | provisioning unique IP addresses. Thus one connection can only | originate from one of the two dsl modems at a time and only use one | modem's worth of bandwidth.
Um...sort-of.
The above is true for the *RETURN* traffic, which will be routed based on IP address.
The problem, however, is with *OUTBOUND* traffic, due to the asymmetrical nature of the DSL connection. It would be perfectly acceptable to send half of the outbound packets via ISP #1, as usual, and the other half of the packets via ISP #2. The trick is, the source IP needs to be the same for *ALL* of the packets.
As long as at least one of your ISPs isn't doing egress filtering for spoofed source IPs, your traffic will get through, and you'll have twice the upload bandwidth (assuming the system you're talking to on the other end can easily handle the out-of-order packet arrival that will likely result).
Setting this up will require some crafty playing with iptables (assuming you're masquerading your internal machines) and the kernel routing tables, but it should be quite possible. Check into the 'ip' command (iproute2) and the lartc HOWTO to get started:
You may also find a pre-canned solution like shorewall easier to implement. Even if you don't go this way, the documentation might be helpful:
http://www.shorewall.net/MultiISP.html
NOTE: If you're willing to forgo the download bandwidth of your additional link, I believe you can use shorewall to combine the outbound bandwidth of multiple links by properly specifying the masquerade addresses used (ie: use the same public IP for all outbound traffic).
I assume there's some reason you can't just get a cable modem, or alternate DSL plan with more upload traffic? That would generally be the easiest solution, and likely cheaper than paying for two separate links.
- -- Charles Steinkuehler [email protected]