I have case where i have 2 CSS's in active standby mode. We use a VIP for radius traffic ie. UDP 1813. When in normal operation, all is OK. The IP src of the packet from CSS to the GGSN (NAS) has the CSS VIP IP. After we failover to the other CSS, this new CSS stops un NATing. This means the the packet from CSS to the GGSN in the radius response has the src IP of the real radius server. The GGSN doesn't accept this as this ip is unexpected.
Why is CSS stopping doing NAT after a switchover. Software is 7.10.504.