Deleting all network interface aliases

I recently needed to move bunch of aliased IPs from one FreeBSD server to another. Adding aliases to /etc/rc.conf and then running ./netstart while in /etc adds new multiplexed IPs to the system all right, but if you need to remove aliased IPs, running /etc/netstart won’t remove them even if the aliases have been removed from /etc/rc.conf. Perhaps there is some easy single command that culls the active alias IPs to those specified in /etc/rc.conf, but I’m not aware of it. The following command can be used to quickly delete all aliased IPs for a specific interface (here “em0″):

ifconfig | grep “0xffffffff” | awk ‘{ print $2 }’ | xargs -n 1 ifconfig em0 delete

For this to work, the netmasks of the aliases and the master IP for the inteface must differ. The netmasks of the aliases are usually set to 255.255.255.255 (hence “0xffffffff”) while the netmask of the master IP is usually something different, specific to your network, e.g. 255.255.255.128 (“0xffffff80″).

Once the above command has been run, /etc/netstart can then be executed to load the remaining or reconfigured aliases (if any) from /etc/rc.conf.

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