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

Forum Discussion

Frank_30530's avatar
Frank_30530
Icon for Altocumulus rankAltocumulus
Mar 28, 2017

Difference between Performance Layer 4 and IP Forwarding (L3) Virtual Server?

I noticed that when I create a Performance Layer 4 VS and do NOT attach a pool to that virtual, this VS behaves similar to an IP Forwarding (L3) VS... (i.e., it will just forward traffic based on th...
application delivery
big-ip
LTM
Soda_Cup_148395's avatar
Soda_Cup_148395
Icon for Nimbostratus rankNimbostratus
Mar 28, 2017

A layer 4 virtual server will allow you to apply and iRule that can perform actions at layer 4 events, like matching against destination port numbers.

 

Both servers will forward the initial SYN to its destination without waiting for the handshake to complete on the frontend. Using these profiles the f5 is effectively routing.

 

Frank_30530's avatar
Frank_30530
Icon for Altocumulus rankAltocumulus
Mar 28, 2017

Hi,

 

Thanks for pointing me to this article. I was looking for some more in-depth information. This article states:

 

Forwarding IP: A Forwarding (IP) virtual server forwards packets directly to the destination IP address specified in the client request. A Forwarding (IP) virtual server has no pool members to load balance.

 

and:

 

A Performance (Layer 4) virtual server has a FastL4 profile associated with it. A Performance (Layer 4) virtual server increases the speed at which the virtual server processes packets.

 

In my config example, both VS (L3 and L4) have no pool(members) attached. Also: a Forwarding IP VS also has a FastL4 profile attached (just like the L4, as the article states).

 

Hence, my question: what is the difference between the two definitions. Perhaps the answer is: in this case they are both identical, but then I wonder, why have two separate versions of the VS instead of just the Performance L4 type, which might behave as an IP Forwarding when you omit the pool?