Hi Guys I have 2 network cards on my debian server. How can I configure it so that my main network card (enp3s0) has 2 ip addresses, 10.0.0.10 and 10.0.0.254. and gateway 10.0.0.2 and dns 8.8.8.8. The second adapter (enp5s0) has ip addresses 192.168.0.254 up to 192.168.4.254 and should get internet through 10.0.0.2

my /etc/network/interface is as follows;
#Main
auto enp3s0
iface enp3s0 inet static
address 10.0.0.10/24
gateway 10.0.0.2
dns-nameservers 8.8.8.8

iface enp3s0 inet static
address 10.0.0.254/24
#Adapter2
auto enp5s0
iface enp5s0 inet static
address 192.168.0.254/24

iface enp5s0 inet static
address 192.168.1.254/24

iface enp5s0inet static
address 192.168.2.254/24

iface enp5s0 inet static
address 192.168.3.254/24

iface enp5s0 inet static
address 192.168.4.254/24

now if the main card is connected the 2nd is dead but i can connect to internet
and if both of them are connected and up no internet connection. how can i solve this?

That's not how gateways work.

A gateway/route is telling the host (not the adapter) how to reach certain non-local IP addresses. If you have two or more routes or gateways pointing to the same network (for instance, a default route pointing to the entire Internet), you've given your system no way to differentiate between the two options.

Practically, what happens is the host (your PC) will attempt to load balance between the two gateways, sending every other packet to a different gateway. The chances of this working is pretty slim, for many reasons.

So you see, when you say "the adapter should get Internet," that doesn't really make sense. The adapter/source IP address is selected after the host has consulted the routing table where the gateway(s) is/are defined.

If redundancy is your goal, adding a second default route with a higher metric could be the way to go.