[ILUG] Load Balancing Over 2 Internet connections.

[Paul Jakma]

On Mon, 5 Sep 2005, Kiall Mac Innes wrote:

> Hi im running an IPCop server and have 2 different internet 
> connections that i need to load balance.. and if one goes down, 
> provide un-interupted connectivity. I dont mind switching from 
> IPCop if its going to make this easier.

> Does anybody have any ideas? so far i can only find info that shows 
> how to do it if both sides of the connection perform some sort of 
> setup (my 2 ISP's are unlikely to do this...)

Ah, then things get hacky:

Write a script to do regular 'quality of service' monitoring on each 
link, using, eg, 'ping' to probe each ISP's gateways, and maybe also 
a set of well-known and reliable remote sites (use the -I interface 
of ping)

If one ISP appears to be doing "badly", remove that ISP from your 
default route. If it recovers, add it back in.

NB: This only works for outbound connections. You'll run into ingress 
filtering at your ISPs if you expect this to work for hosting 
externally accessed services (eg www). For stuff like SMTP just list 
both IPs in DNS.

NB2: Outgoing connections will only work if they originate from the 
machine connected to both ISPs. Ie it won't work for machines behind 
a multihomed router without further hackery (eg NAT, or source 
routing).

regards,
-- 
Paul Jakma	paul at clubi.ie	paul at jakma.org	Key ID: 64A2FF6A
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