SNAT Preserve-Strict not working with two different source addresses

Hi everybody. I have a BIG IP LTM 4000s 12.0 and the following issue.

 

I have an endpoint (EP) that needs to receive packets from a determined IPv6 address (IPXX) and source port (SrcPortYY), otherwise, it will not respond to it.

 

I have two servers (A and B) that send packets destined to this endpoint through a BIG IP. I configured a SNAT to translate to IPXX address when it receives either from A or B and also to Preserve-Strict the source port it receives.

 

When I send packets first from A to EP, the BIG-IP translates the source address correctly to IPXX, keeps the source port SrcPortYY and everything works fine. But when I start to send from B to EP and still sending from A, that translation fails and keep translating only the packets that it first received from A.

 

Any ideas? Thanks!

 

Example:

 

Start sending from A

 

A:SrcPortYY > EP:DstPort --> Original packet

 

IPXX:SrcPortYY > EP:DstPort --> Translated packet OK

 

A:SrcPortYY > EP:DstPort --> Original packet

 

IPXX:SrcPortYY > EP:DstPort --> Translated packet OK

 

Start sending from B and still sending from A

 

B:SrcPortYY > EP:DstPort --> Original packet and no translation

 

A:SrcPortYY > EP:DstPort --> Original packet IPXX:SrcPortYY > EP:DstPort --> Translated packet OK

 

B:SrcPortYY > EP:DstPort --> Original packet and no translation

 

A:SrcPortYY > EP:DstPort --> Original packet

 

IPXX:SrcPortYY > EP:DstPort --> Translated packet OK