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Qasim's avatar
Qasim
Icon for Cirrostratus rankCirrostratus
Jul 12, 2019
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What LTM do to HTTP Header?

Hi,

 

I need to read up on LTMs as its a basic theory question but wondering if you can help me in the meanwhile:

my understanding is that LTM receives traffic on a particular VIP, replaces the header with the backend server name/IP and forwards it - am I correct?

 

if so, Anyway I can get LTM to keep the original header when forwarding to the pool members? its just that we have NGINX as a backend that is configured for header based routing.

 

Thanks in advance.

  • Lee_Sutcliffe's avatar
    Lee_Sutcliffe
    Jul 12, 2019

    It's not something that can be turned on with a check box, you need to either:

    • Use and iRule (one above is not re-writing the Host)
    • Use a Local Traffic Policy
    • Use an HTTP profile to erase a header

     

    Are you sure F5 is rewriting the Host? Can you share you VS config?

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  • Lee_Sutcliffe's avatar
    Lee_Sutcliffe
    Icon for Nacreous rankNacreous
    Jul 12, 2019

    F5 will not re-write a Host header by default, you would need to configure it to do so.

    The default configuration would be

     

    Client ((Host header some.host.com) -> VIP -> Pool (Host header some.host.com)

     

    So in your example, NGINX could still do the header based routing

  • Qasim's avatar
    Qasim
    Icon for Cirrostratus rankCirrostratus
    Jul 12, 2019

    Thank Lee once again.

    if I was to enable the re-write, what would I need to do? is it like a checkbox somewhere? wondering if this has been enabled for a service I am t-shooting right now.

     the current IRULE only redirects so can't be the irule:

    when HTTP_REQUEST {

      switch -glob [HTTP::host] {

    uat-services-hccf.abc.co.uk { pool EXT_UAT_abc_443_POOL }

    thanks.

    • Lee_Sutcliffe's avatar
      Lee_Sutcliffe
      Icon for Nacreous rankNacreous
      Jul 12, 2019

      It's not something that can be turned on with a check box, you need to either:

      • Use and iRule (one above is not re-writing the Host)
      • Use a Local Traffic Policy
      • Use an HTTP profile to erase a header

       

      Are you sure F5 is rewriting the Host? Can you share you VS config?

      • Qasim's avatar
        Qasim
        Icon for Cirrostratus rankCirrostratus
        Jul 12, 2019

        I am not sure as I don;t have access to the logs but was just wondering whether that the case and if I can confirm it from the config.

         

        SO it won't replace the header even if offload SSL