Jails - IP Addresses

Each time a jail is started, FreeBSD's jail(8) utility will tell ifconfig to create a simple alias to your jail's designated ip address. However that only occurs on the FreeBSD host machine. In most situations, your local network is under the control of a local router. So to prevent ip address conflicts elsewhere you should reserve your jail's ip address on your local router too.

Reservation Strategies

1) Use High-IPs

Most router DHCP servers usually allocate ips in ascending order. So one strategy is simply give jails a high-enough ip addresses that they will not be likely to cause conflicts.

2) Alter the DHCP range

Optionally, you may also decide restrict your home router's DHCP allocation range. The requires going into your router's DHCP settings and changing the first / last IP address.

3) Static DHCP - Multi-IP

This option depends entirely on your router's capabilities. Unfortunately for most home routers it's not possible to assign multiple static IPs to the a single mac address. Normally only 1 IP can be assigned to each MAC address and no more. However if your specific router supports it, then by all means use this method.

4) Static DHCP - fake MAC address

If your router does not support method 3), you may still be able to use Static DHCP. Just create your "static DHCP" entries with FAKE mac addresses.