Bluecoat: The Difference Between Proxies

The Difference Between Proxies

This article describes the terminology and basic differences between proxies.

Forward proxy

The proxy is on the same networks as the clients

If a proxy manages all outbound traffic to the web, it is a forward proxy!


Reverse proxy

The proxy is on the same network as the servers (inbound)

If a proxy sits in front of several web servers and uses round robin to balance the load, it is a reverse proxy!


Explicit Proxy

In an explicit proxy, the client is configured to communicate with a proxy.


Transparent Proxy

In a transparent proxy, the client attempts to communicate directly with a site and the request is intercepted.


Neither of these options is configured on the Proxy SG.


Proxy Configuration Notes – Explicit Proxy

  • Requires client config (ie proxy settings in browser)
  • Src:client Ip    DST: SG IP    >     Src:SG IP    DST:Server IP
  • Application must be proxiable
  • One way to deploy explicit proxy can be to use a PAC file.
  • Another method is Proxy Auto-discovery.
  • Recommended method is group policy.
  • Traffic must match a service policy


In explicit proxy, when a connection is made for a service that is not running on ProxySG, the connection is rejected.


Proxy Configuration Notes – Transparent Proxy

  • The SG intercepts the requests.
  • Option: reflect Client IP can make the SG spoof the client IP – it is rarely used but can reflect accurate sources on servers where required. This is a global option.
  • Transparent proxy can use WCCP to redirect traffic or a layer 4 switch can be used to rewrite the MAC. Last but not least, Load Balancers can be used.
  • A transparent proxy also does its own DNS lookup but can be turned off (Trust Destination IP).
  • If the proxy is in bridging mode or acting as a gateway, a service group does not need to be matched.
  • Routing modes requires IP forwarding enabled



The proxysg can also be used as a default gateway but is not recommended.


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