Forum Discussion

Altostratus

Feb 10, 2026

Solved

TCP Profile with Verified Accept enabled and three-way TCP handshake

Hi, I'm trying to understand exactly how the Standard virtual server processes connections using the full proxy architecture works when Verified Accept is enable on the TCP profile. With Verified A...

BIG-IP

LTM

tcp profile

zamroni777
Feb 13, 2026
with verified accept: server side 3 way handshake completes before f5 replies SYN-ACK to client's SYN

JoseLabra

MVP

Feb 10, 2026

Hiii Diego, how r u?

With Verified Accept enabled, the BIG-IP completes the server-side three-way handshake before completing the client-side handshake. The client does not receive a SYN-ACK until the selected pool member has successfully responded to the SYN. This guarantees that the connection is only accepted if a backend server is actually reachable

diego2
Altostratus
Feb 11, 2026
Hi Jose, thank you for your reply.
The client does not receive a SYN-ACK until the selected pool member has successfully responded to the SYN, ok. But the ACK to the pool member that complete the three-way server-side handshake is sent before or after the SYN-ACK to the client ?
Is the SYN-ACK that the server sent to reply to the SYN of the Big IP the guarantee that the connection is accepted ?
If the server-side three-way handshake occurs before the client-side three-way handshake, what it means that :
Verified Accept enabled: CLIENT_ACCEPTED -> LB_SELECTED -> SERVER_CONNECTED -> HTTP_REQUEST -> HTTP_REQUEST_SEND

Thanks
- zamroni777
  MVP
  Feb 13, 2026
  with verified accept: server side 3 way handshake completes before f5 replies SYN-ACK to client's SYN
  - diego2
    Altostratus
    Feb 13, 2026
    Ok, thank you for you reply.
    So, could you help me understand exactly what that means
    CLIENT_ACCEPTED -> LB_SELECTED -> SERVER_CONNECTED -> HTTP_REQUEST -> HTTP_REQUEST_SEND
    
    Thanks