Will configuring CARP cause an outage?

[ttblum]

Hello,

I currently have a pfSense 2.0.1 router deployed and I would like to add a second router for hardware redundancy.  Will configuring CARP for this require taking my existing router offline?

Thanks,

Todd

[cmb]

You have to change your interface IPs to CARP IPs, which requires having the interface IP (your default gateway internally, and destination IP on WAN-side traffic) removed briefly. Generally that can be done quickly enough that it doesn't impact any hosts that are already online, or any inbound traffic as long as it's shorter than the period of the ARP cache, which it'll easily be. I've done it many times on production networks on the fly without dropping a packet, but you need to be careful to be ready to add the CARP IP immediately upon changing the interface IP or it's possible you'll create an outage until the CARP IP is added. I always have the CARP IP ready to save, change the interface IP, save the CARP IP. In that case it's just a matter of how quickly you can apply changes on one tab, and click Save and Apply on another.