which IP does F5 LTM use as its Source IP address to perform healthcheck monitors .

It uses routing - ie it will follow it's self-IP/specific route/default route etc

Hi Pete, thanks for responding!

I understand the self IP and routing options in terms of interface, but I must be missing something... If I have two IP's on the same interface that is also used for the default route, which one would it choose [out of the box].

For clarity:

• 10.1.1.8 and 10.1.1.10 are both "traffic-group-local-only" addresses on the same BIG-IP
• Both are on VLAN1100 [called "DC1_LBNET"], Physical Interface 0.3
• Default route is via 10.1.1.1 [default gateway] on interface "DC1_LBNET"
• For any network that the BIG-IP is not directly connected to, and where the default route is used - which IP address will it use to source the Health Monitor / TACACS requests etc?

I ask because I have just rebooted two BIG-IP appliances that have this configuration, and the health monitors were using say 10.1.1.10, but after reboot switched to using 10.1.1.8. The latter IP was configured after the last reboot to be used for BIGIP DNS but this was the 1st time it has been rebooted since.

Am I missing something fundamental here?

Thanks, Don

I see what you mean Don, i've never come across that issue actually. My suggestion would be to do some testing to see which it uses and work it out.