Can you elaborate on your network topology and NAT?
Out bound traffic from 95.130.9.210 goes via 95.130.9.1 then 95.130.8.1 then out to the real world.
outbound: [ 95.130.9.210 ] --> [outbound gw 95.130.9.1 ] --> [2th hop 95.130.8.1 ] --> inet
In bound traffic comes via 95.130.8.11 then 9.130.8.120
inbound: [ 95.130.9.210 ] <-- [ 9.130.8.120 ] <-- [SNAT:95.130.8.11 ] <-- inet
It's NATted at 95.130.8.11 and all I see is this address connected to the system(ie all connections show as 95.130.8.11).
My /etc/network/interface - the DNS server is temporary for testing.
If I understood you correctly and they are simply replacing the source IP of all incoming packets I'd say this is broken network and ask them to fix it. (it will break more than just DNS resolution unless they are NATing only on specific protocols [udp] and ports [53]).
auto enp4s0 iface enp4s0 inet static address 95.130.9.210 netmask 255.255.255.255 network 95.130.9.210 broadcast 95.130.9.210 dns-nameservers 95.130.8.8 95.130.8.9 #Route statique vers la passerelle up ip route add 95.130.9.1 dev enp4s0 up ip route add default via 95.130.9.1
up ip addr add 95.130.12.251/24 dev enp4s0 up ip addr add 95.130.12.252/24 dev enp4s0