How to connect multiple USB modems?

Question

linux

Hello
There is a machine on debian, 2 usb modems are connected to it.
But the problem is that the second one causes a conflict of ip addresses.
How to solve this problem?
I tried to register in /etc/network/interfaces like this, but there is no reaction, it still assigns its own address

auto eth1
iface eth1 inet static
address 192.168.8.101
gateway 192.168.8.255
netmask 255.255.255.0

auto eth2
iface eth2 inet static
address 192.168.9.101
gateway 192.168.9.255
netmask 255.255.255.0

ifconfig

eth1      Link encap:Ethernet  HWaddr 00:1e:10:1f:00:00  
          inet addr:192.168.8.100  Bcast:192.168.8.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:251 errors:0 dropped:0 overruns:0 frame:0
          TX packets:112 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:92254 (90.0 KiB)  TX bytes:13675 (13.3 KiB)

eth2      Link encap:Ethernet  HWaddr 00:1e:10:1f:00:00  
          inet6 addr: fe80::b0b4:a7ba:fee8:b03/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:83 errors:0 dropped:0 overruns:0 frame:0
          TX packets:27 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:36038 (35.1 KiB)  TX bytes:4785 (4.6 KiB)

Answer 1

мак-адреса одинаковые, попробуйте сначала их поменять.

Answer 2

Попробуйте через udev задействовать GNU MAC Changer