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F5 LTM – VS types

It took me a while to dig out on F5 web site the real difference between different VS types in LTM… so here are some self-explanatory diagrams for quick reference in future (just the main profiles here – omitting the exotics like DHCP Relay and SIP message routing):

  • Standard (TCP):f5-standard-tcp
    Main principle – TCP handshake on the client-side has to complete before TCP handshake on the server side get started.This is a classical “full proxy” from F5. Not “L7-aware” so not very useful for web servers…

  • Standard TCP + L7 profile (e.g. HTTP):f5-standard-tcp-plus-L7Main principle – TCP handshake on the server side won’t start until the client sends first L7 request.

    This is the most flexible and popular type for HTTP/HTTPS traffic allowing all features which BigIP is so loved for around the world! The sky is the limit for iRules on Standard VSs!

  • Performance L4f5-performance-L4main take aways:
    – uses PVA/ePVA hardware acceleration which means it may be noticeably quicker than standard VS
    – in iRules you cannot use events above L4

    here is a very good comment from F5’s director of architecture with regard to PVA acceleration:

    • No HTTP optimizations
    • No TCP optimizations for server offloading
    • SNAT/SNAT pools demote PVA acceleration setting level to Assisted
    • iRules limited to L4 events, such as CLIENT_ACCEPTED and SERVER_CONNECTED
    • No OneConnect
    • Limited persistence options:
      • Source address
      • Destination address
      • Universal
      • Hash (BIG-IP 9.x only)
    • No compression
    • No Virtual Server Authentication
    • No support for HTTP pipelining
  • Performance HTTP:with idle flow on the server side:
    f5-performance-httpwithout existing idle flow:

    This one is in essence a combination of some TCP optimizations, OneConnect and FastHTTP profiles. According to F5 it is meant to be used under “ideal” traffic conditions. In my view the limitations make it quite useless in real life:

    • SNAT must be used
    • No IPv6 support
    • No SSL offload
    • No compression
    • No caching
    • No PVA acceleration
    • No virtual server authentication
    • No state mirroring
    • No HTTP pipelining
    • No TCP optimizations
    • Limited iRules support L4 and are limited to a subset of HTTP header operations, and pool/pool member selection

Very good use scenario from my perspective would be a VS for a pool of web servers supplying “dumb” static content where you just need pure performance and no intelligence available with the standard VS and “normal” HTTP profiles.

  • Forwarding L2:f5-forwarding-L2
  • Forwarding IP (L3):f5-forwarding-IP
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