How to redirect unknown users from one subnet to another ubuntu OS?

Question

FreeBSD

How to create a transition to the address 172.32.0.1 from one subnet 172.32.0.0? I have a manual on how to make this setting in freebsd, how to convert it to ubuntu 12?
1. In freebsd dhcp config:

subnet 172.32.0.0 netmask 255.255.240.0 {
default-lease-time 3600;
option domain-name "isp";
option subnet-mask 255.255.240.0;
option domain-name-servers 172.32.0.1;
option routers 172.32.0.1;
range 172.32.0.100 172.32.0.254;

2. In freebsd alias in /etc/rc.conf:

ifconfig_em0_alias0="inet 172.32.0.1 netmask 255.255.240.0"

3. In freebsd wrap itself, for this subnet in /etc/firewall.conf:

unknown users redirect
${FwCMD} add 5 fwd 127.0.0.1,80 ip from 172.32.0.0/20 to not me dst-port 80

How to do this in Ubuntu?

Answer 1

So this is completely different. According to your link, as I understand it, they are trying to build a captive portal. But for these purposes, there are ready-made solutions. pfsense for example

Answer 2

I'm sorry, maybe I didn't add something, you need to do it this way, when someone wants to open the vk.com website, it will be transferred to 172.32.0.1.