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Frank_30530
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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 the route table of TMM):

L4: tmsh create ltm virtual vs_ipfwdL4 { destination 0.0.0.0:any }

L3: tmsh create ltm virtual vs_ipfwdL3 { destination 0.0.0.0:any ip-forward }

Is there any (subtle) difference in the behaviour (or inner workings) between the above two definitions?

-Frank

7 Replies

  • 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

      Thanks for the answer.

       

      I know that you can do a lot more with Performance L4 VS, and I found out that both VS seem to be effectively routing (L3) traffic on a packet-per-packet basis.

       

      However, are both L3 and L4 vS definitions indeed equal, or are there some 'hidden' (subtle) differences that I did not notice?...

       

    • Frank_30530's avatar
      Frank_30530
      Icon for Altocumulus rankAltocumulus

      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?

       

  • When you configure Forwarding (IP) VIP, you will be forwarding the traffic without doing any further enhancements to increase the traverse time.

     

    For layer 4 forwarding VIP, there is a profile called fast forward applied and it will enhance the packet speed using the layer 4 techniques (Packet Velocity Accelerator etc) which increases the performance.

     

    -Jinshu

     

  • you know why fowarding vs l2、forwarding vs l3、performance l4、standard vs was designed ?when you use more higher layer vs, it reduce your performance of device, l3 means you don't care what is in layer 3+ if it meets your needs。

     

    eg:i must use performance l4 ,since forwarding vs l3 don‘t fulfill my’s needs ,i want to add some irule or l4 load balance , of course .then my need have changed,i need ssl offload,i need rewrite url, why not upgrade to standward vs ? performance l4(no pool member) and forwarding vs l3's funcation may be the same ,i prefered forwarding vs l3