I have a 3640 with IOS 12.4.8c, and I have set up Server Load Balance virtual servers with their corresponding real servers (not using NAT).
This works fine with this IOS release.
I have tried updating to: 12.4.10; 12..4.12 and 12.4.13 but with all of these newer releases SLB hangs, which means that TCP/UDP requests stop being forwarded to the real servers after an amount of time measured in hours.
When SLB hangs, a power cycle restores the service and the problem represents itself only after several hours of service (usually within36 hours).
It is quite hard to debug this problem because it takes so long for it to manifest, and when it does, given that this router is in a live environment, the router is immediately power-cycled and then downgraded at the first opportunity back to 12.4.8c that works without problems.
Is there a Cisco engineer who may have an idea of what could be wrong?