Re: [LARTC] 2 gateways out

Linux Advanced Routing and Traffic Control

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On Sun, Sep 23, 2001 at 03:04:52PM -0400, Largo Hellenz wrote:

> >This depends greatly on what's on the other side of the cable modems - are
> >there two separate ISPs?
> 
> yes. two different providers.

Ok. This rules out a lot of fancy tricks.

> so i would ping both of my two gateways via the cronscripts and, if the
> current
> default gateway is down, and the standby is up, then change default gateway?

With policy routing, you can have multiple default gateways.

> so policy routing dynamically routes based upon available paths on the fly?
> could anyone provide an example that just cuts traffic equally between the
> two?

Well, you could try something like this:

# ip route add default nexthop via 10.0.0.1 dev eth0 \
	nexthop via 10.0.0.202 dev eth1

Not sure if this is 'sticky'. This might just assign TCP sessions to a
single cablemodem, then again, it might not. I would vote against this. Your
users would also fall victim to the 'AOL Proxy Problem'. In the midst of
browsing a site, they continually appear from two different IP addresses,
which may upset loadbalancing tools.


> lets say someone was was browsing cars.com and it was 10 hops from one ISP
> but only 5 from the other.... can policy routing tell those packets to use
> the shorter path?  or is this something that routing daemons are for?
> or is there another way to solve this puzzle?

You could try tricks with squid, which has been known to have some kind of
support for this. Your best best is to have multiple route tables, and route
these tables differently.

This page appears to be relevant: 

              http://mlarchive.ima.com/linux-net/1999/3495.html

> do you mean droping these commands in an init script so they always come up
> at boot time? or something else?

These modules can be autoloaded by the kernel. Make sure that you have
modutils 2.4.x!

Regards,

bert

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