I have put up two networks, but when testing one server does not take
the next metric

This is the situation

route gateway metric 1
route gateway metric 2

FIREWALL-1 --- the_internet

FIREWALL-2 --- the internet

Now if I add a rule in firewall-1
iptables -s -j REJECT
I cannot ping to the internet!
It just gives me: host unreachable

Why does it not takes the next route then?

This setup is for redundancy, if one connection with the firewall goes
down, we transfer all the traffic to the other one (Dynamic DNS).
But it seems that the servers don't switch to the other network if 1 is