Univention Corporate Server - Extended IP and network management documentation#
Advanced proxy configuration#
Cascading of proxies#
In some scenarios, cascading of proxy servers may be required. In such a setup, individual proxy servers access logically superordinate proxy servers when web sites are opened, which then fetch the requested data from the internet. This allows creation of a hierarchical structure of proxy servers and, for example, the operation of a central cache in a company’s headquarters that the proxy servers at the individual company sites can access.
The superordinate proxy server is referred to as a parent proxy. The parent
proxy can be specified via the Univention Configuration Registry variables
(IP address or hostname) and
squid/parent/port (port number).
Proxy requests from computers in the proxy server’s local network are answered
directly and not forwarded to the parent proxy. If additional networks should be
excluded from forwarding to the parent proxy, these can be specified via the
Univention Configuration Registry Variable
squid/parent/directnetworks. When doing so, the CIDR
notation must be used (e.g.
24); several networks should be
separated by blank spaces.
Operation as a transparent proxy#
It is possible to configure Squid as a transparent proxy. This can help avoid configuring the proxy server in all application programs. When using a transparent proxy, all unencrypted web queries are automatically rerouted through the proxy server.
This only works for unencrypted web traffic, not for
LDAP authentication on the proxy server must not be enabled.
The following configuration steps need to be made:
The proxy server must be configured as the default gateway on all clients.
The proxy server must be configured to use IP forwarding.
$ echo "net.ipv4.ip_forward = 1" >/etc/sysctl.d/ip_forward.conf $ sysctl --system
The Univention Configuration Registry Variable
squid/transparentproxymust be set to
yeson the proxy server. After that Univention Firewall and Squid need to be restarted:
$ systemctl restart univention-firewall squid
This enables packet filter rules which redirect all queries for the web ports to the proxy server.