On Apr 20, 2011, at 11:25 AM, Lee Brown wrote:

> Hi,
> 
> I have a multi-ISP situation (working well) whereby I need to turn off one of 
> my ISP's once a cap has been reached.
> I can turn it off quite easily by replacing the default route in the main 
> table:
> default
>         nexthop via 10.1.5.3  dev eth1.5 weight 1
>         nexthop via XX.XXX.XX.33  dev eth1.9 weight 1
> 
> with
> default via 10.1.5.3 dev eth1.5
> 
> But if I try to reverse the process and replace the default route with the 
> 1st one, packets routed via the eth1.9 provider goes into a black hole (not 
> investigated where packets end up)

It's not the outgoing packets that are the issue, I'm betting, but rather that 
incoming packets suddenly become martians (you can confirm that by looking at 
your kernel log). Turn off routefilter on both of your interfaces and it should 
work better. Note, however, that if the ISP through which eth1.5 connects is 
doing egress filtering, then that ISP will drop traffic whose source is 
XX.XXX.XX.33.

> 
> Doing a shorewall restart takes several minutes, so I'd like to avoid that if 
> possible, but it always puts things the way they should be.

You must be using an ancient version of Shorewall with the shell-based rules 
compiler. If you upgrade to the current version, I'm betting that restart will 
be fast (and it will be seamless).

> 
> I'm thinking the direction I should be going in is either:
> 1. To insert/delete an iptables rule to mark the packets for the always-on 
> ISP when the variable ISP has expired (per the FAQ)
> 2. Generate 2 sets of rules for iptables using shorewall (one with multi-path 
> default route, one with single path) and swap one for the other.

I would try the routefilter thing first.

-Tom

Tom Eastep        \ When I die, I want to go like my Grandfather who
Shoreline,         \ died peacefully in his sleep. Not screaming like
Washington, USA     \ all of the passengers in his car
http://shorewall.net \________________________________________________


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