Let's say you have a /29 network on your DSL subscriber (dial) line: 212.218.10.64/29.

In that case you could use six ip adresses (65 to 70) as public addresses for machines or services behind your firewall.

According to this thread and this thread it is not possible. But it is possible - and i will show you how.

snippet.bash

  212.218.10.65,on,RED2
  212.218.10.66,on,RED3
  212.218.10.67,on,RED4
  212.218.10.68,on,RED5
  212.218.10.69,on,RED6
  212.218.10.70,on,RED7

/etc/rc.d/init.d/networking/red.up/02-aliases:

snippet.bash

  ip addr add 212.218.10.65/29 dev ppp0
  ip addr add 212.218.10.66/29 dev ppp0
  ip addr add 212.218.10.67/29 dev ppp0
  ip addr add 212.218.10.68/29 dev ppp0
  ip addr add 212.218.10.69/29 dev ppp0
  ip addr add 212.218.10.70/29 dev ppp0
  ip addr show ppp0

snippet.bash

  chmod 0755 /etc/rc.d/init.d/networking/red.up/02-aliases

READY.

• The new ip addresses will be automatically configured every time the firewall reconnects or reboots.
• You will see the addresses in the ipfire menu → network → aliases
• You can use the new addresses in the firewall config - they will appear as RED2 - RED7
• The warning “Aliases will not be active unless your RED interface is STATIC” can be safely ignored from now on

Have fun