[LARTC] Redundant Internet connections [Updated]

["Seth J. Blank" <sblank@cms-forex.com>]

Sorry, I really wasn't paying attention when I wrote this (i.e. I've had 
no sleep).

I have the routing tables working properly for the internal network.

What I need to do is have the routing tables update the gateways when a 
line is down.

i.e.    intranet ----- firewall ----- router1 ----- internet
                 \-- router2 ----- internet
Currently, I have the gateway from the firewall being nexthops between 
router1 and router2. This works fine. But what I need to do is have the 
firewall check the links between router1/2 and the internet and switch 
gateways if a line is down.
What I want to do, but can't figure out how to, is send out a packet 
through router1 and see if it gets an arbitrary number of hops (probably 
3) out. If not, switch the default route to use the other gateway. This 
needs to be done for both gateways, and there also needs to be a route 
to restore the gateways when the line goes back up.

Any help would be greatly appreciated.

Thanks so much,
Seth J. Blank
Systems Operations
Capital Market Services, LLC

Seth J. Blank wrote:

> I have a firewall with two redundant internet connections coming in 
> (eth0 and eth1) and an intranet behind eth2.
>
> What I am trying to do is have data off of eth2 split evenly between 
> eth0 and eth1, and if one interface goes down, to fully utilize the 
> other.
>
> What I'm trying to do is have all data from eth0 be passed on to eth2 
> (unless it's stopped by the firewall), same with eth1, and all data 
> from eth2 be split evenly between eth0 and eth1.
>
> currently I have the following routes and rules to accomplish this:
>
> ip route add 10.0.0.0/8 via GATEWAY0 table 1 proto static
> ip route add 10.0.0.0/8 via GATEWAY1 table 2 proto static
>
> ip route add default table default scope global nexthop via GATEWAY0 
> dev eth0 weight 1 nexthop via GATEWAY1 dev eth1 weight 1
>
> ip rule add pref 1500 iif eth0 table 1
> ip rule add pref 1501 iif eth1 table 2
> ip rule add pref 100 iif eth2 table default
>
> This does NOT work properly.
> From localhost, everything works perfectly. I can bring up and down 
> interfaces and everything works properly and transparently.
> But, from the intranet, everything stops. With a different default route:
> ip route add default via GATEWAY0 dev eth0 table default
> everything is fine from both localhost and the intranet. Same with 
> GATEWAY1 eth1.
>
> Can anyone offer advice on how to resolve this problem?
> The only way I can think of so far is a remarkably simple but stupid 
> hack, where I just ping -I eth0 GATEWAY0 and ping -I eth1 GATEWAY1 
> every thirty seconds or so and switch default routes if an interface 
> is down. This obviously does not solve the problem, nor allow 
> bandwidth to be shared across both lines.
>
> Any help would be greatly appreciated.
>
> Seth J. Blank
> Systems Operations
> Capital Market Services, LLC
>
>
>
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