yum update could not retrieve mirrorlist

Pepe asked:

Im trying to install a web service with centos 7 apache and sql server. For that purpose, Im using VMware, the installation of OS finish successfully but when I try to update centos it gives me this error:

#yum update
Could not retrieve mirrorlist http://mirrorlist.centos.org/?release=7&arch=x86_64&repo=os&infra=stock error was 14: HTTP Error 403 - Forbidden

The thing is, this is a remote machine (from the company Im working with) and Im almost sure they are using somekind of firewall/proxy. When I do:

#curl -v mirrorlist.centos.org
>get /?release=7 http/1.1
>user-agent: curl/7.29.0
>host: mirrorlist.centos.org
*http 1.0, assume close after body
<http/1.0 403 forbidden
<content-lenght: 479
<content-type: text/html
<server: mikrotik httpproxy
<proxy-connection: close

Is the network under a proxy? If it is how can I prove this in order to show my boss and start setting up the web service. I cant install nothing either.
Thank you, regards.
EDIT: I forgot to mention that I can browse to http://mirrorlist.centos.org/?release=7&arch=x86_64&repo=os&infra=stock on chrome without problems and see all urls in the host (windows 10).

My answer:

You’ve already proved that the server is behind a proxy, because the proxy that intercepted the request identifed itself as mikrotik httpproxy. What to do about it depends on what that Mikrotik device is, why you’re proxying to it at all, and what it’s meant to be doing.

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