Resolve a hostname by BIG-IP it's self, when to use "HTTP exlicit proxy"

Hi Guys.

I'm looking for a way to resolve the hostname by not using "DNS resolvers", when to use "HTTP explict proxy".

My goal is to resolve the name of the internal web server by BIG-IP it's self when bigip is as a proxy. Trying to modify /etc/hosts as a test and access to the virtual server, which is configured as Proxy, from my client but couldn't resolve the name as below.

/etc/hosts

     cat hosts
    
     THIS IS AN AUTO-GENERATED FILE - DO NOT EDIT!!!
    
     Use the tmsh shell utility to make changes to the system configuration.
     For more information, see tmsh -a help sys global-settings.
    .
    
    .

    172.18.20.80      www.sample.xyz
    `

The result of typing curl to access to my proxy virtual server.

    > curl -x 192.168.19.101:3235 -L http://www.sample.xyz
    DNS lookup failed

Does anyone have any ideas? Even though I could use irule, would it be a bit difficult?