cks4a://`` schemes in
    your ``proxy_url`` to ensure that DNS resolution is done from the remote
    server instead of client-side when connecting to a domain name.

SOCKS4 supports IPv4 and domain names with the SOCKS4A extension. SOCKS5
supports IPv4, IPv6, and domain names.

When connecting to a SOCKS4 proxy the ``username`` portion of the ``proxy_url``
will be sent as the ``userid`` section of the SOCKS request::

    proxy_url="socks4a://<userid>@proxy-host"

When connecting to a SOCKS5 proxy the ``username`` and ``password`` portion
of the ``proxy_url`` will be sent as the username/password to authenticate
with the proxy::

    proxy_url="socks5h://<username>:<password>@proxy-host"

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