PF and NAT on 2 parallel inet connections

[Claudiu <dr_(_dot_)_clau_(_at_)_rdslink_(_dot_)_ro>]

Hello,

I have this situation: a gateway with 2 internet connections on 2 
different interfaces, from 2 different ISPs. There is no IP that can be 
routed by both ISPs.
What I want to to obtain is not exactly load balancing, but I want to 
use the first connection, and if it falls, the second should be used.
This should be done by means of NAT, for an entire network which is 
behind this gateway.

Can you give me some advice regarding this situation ?

I am thinking of a simple solution which is: checking if the connection 
is ok (by pinging maybe) if the connection is not ok, just load another 
set of rules.
But this way I will loose the power of securelevels, because afaik the 
rules cannot be changed while in a high securelevel.

Thank you in advance.

With respect,


--
Claudiu