Connection Rate Limit Mode - Per Source Address

Hi Deepsri , 

It works per source address subnet masks which you as admin sets the mask on the virtual server optins. 
This is a piece of info in bigip GUI : 
"
Connection Rate Limit Source Mask

Specifies an IP address mask, in bits, to be applied to the source address as part of the rate limiting. The default is 0, which is equivalent to using the entire address, 32 in IPv4, or 128 in IPv6.
"

It should give you stable results based on subnet mask that you set. 

Note that , Connection Limits have not allowness if the connections per source address subnet mask exceed the defined limits , so you have to properly set the mask value and the limit as well. 

Also , 

Have a look in the following article , you may hit in this BUG : https://my.f5.com/manage/s/article/K17082

I hope this helps you