Mar 27, 2026 - For details about updated CVE-2025-53521 (BIG-IP APM vulnerability), refer to K000156741.

Forum Discussion

OcasionalLB's avatar
OcasionalLB
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Mar 24, 2020

Why is Loose Close needed with nPath

Hello,   I had a case today where I was load balancing traffic to a web server with nPath (Direct server return). I encountered problems with certain API endpoints where, due to the code, there w...
application delivery
LTM
PeteWhite's avatar
PeteWhite
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Mar 24, 2020

Loose init is more normally the issue with nPath although they generally go together - loose close allows any fin packet to remove the flow. As to why it was the issue, I suggest you do some more investigation to see what was going wrong previously - it was probably related to the source port preservation rather than the loose close

OcasionalLB's avatar
OcasionalLB
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Mar 24, 2020

F5 manual says to enable Loose close when configuring nPath.

 

In my case, if I disable Loose close, it stops working. Looking at the tcpdump from the client and the server, I can see servers sending content back to the client, client is ACK-ing it, but the ACK is never passed from F5 to the server. This is why I suspect the F5 removes the connection from connection table, but I'm not sure why. As soon as I enable Loose close, it starts working.

 

Idle timeout was set to 300s and TCP close timeout to 5s.