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I have 2 adls links with 192.168.1.1 internal ip boths. ADSL1 allow internet web access to all internet domains, and ADSL2 allow web access only to domains of my country. At this moment, i have a Debian 11 server as non-transparent proxy-firewall to 192.168.0.1/24 network with one nic card connected to ADSL1, and i need connect the second ADSL and use it only for web request to my country domains accross the proxy service installed.

Note: it´s not possible for me change the internal´s ip address of adsl modems

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  • why should it not possible to change the ip of your own devices at all?
    – djdomi
    Dec 19, 2021 at 18:25
  • @djdomi the network provider install on my institution two adls lines very very long time ago, to make this kind of change its necesary a burocratic process
    – Francisco
    Dec 19, 2021 at 19:46
  • then contact one of both, or you have to use other routers in front of the device to separate them and use that wqy, but else the answer is correct imho
    – djdomi
    Dec 20, 2021 at 14:06
  • Questions on Server Fault must be about managing information technology systems in a business environment. In case this adsl lines are in a business environment i can and will contact or resolve the issue on the point of installation or escalate to the responsibility person. We have now an ofdtopic situation
    – djdomi
    Dec 20, 2021 at 14:08

3 Answers 3

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You cannot do this without changing the IP address.

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  • Ok, i will check with the network provider the ip configs
    – Francisco
    Dec 20, 2021 at 16:12
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What are you trying to accomplish with those two ISPs? Is it redundancy (fail-over) or it is for load-balance(active-active)? The truth is that you can do both, if fail-over, then it's all about one-liner script to brings up second interface if internet connection drops (ping fail for example) and you no need to worry about duplicate addresses. The load-balance will be a little bit more tricky because you should apply some algo to distribute sessions across both interfaces, but if you already solved that, then your solution will be, again, a simple one-liner which compare interface1 ip with interface2 ip and if they are from the same subnet(or gateway ip is equal) just do a dhcp renewal request to the isp of your choise.

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  • The idea is to route all outgoing traffic destined for domains in my country to the network interface connected to modem # 2, and the rest of the destinations on the internet to the network interface connected to modem # 1. The problem is: the 2 modems have the same internal ip address (192.168.1.1). I really do not think it can be called load balancing or failover to what I want to do; maybe it's load balancing.
    – Francisco
    Dec 22, 2021 at 23:46
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If you can ensure your dhcp_client IPs are different (but with same gateway address), you should be able to setup destination-policy routing via interface(not via ip). .. I think that can be also accomplished with pseudo network interfaces and network bridge interfaces binds. But firstly try to route via interface

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