Streaming Media Supplement sa2150 and sa2250

9
Chapter 2 Media-IXT Deployment Scenarios
When the layer 4 switch provides transparency, there is a single connection from the client to Media-IXT. The
layer 4 switch’s MAC-level redirection does not break this connection.
Reverse proxy caching
In reverse proxy caching, Media-IXT acts on behalf of specific origin servers. Reverse proxy depends on the
interaction between:
• an origin server or group of origin servers
• the URLs of the content on the origin server
• a single Media-IXT, or a Media-IXT cluster
• the advertised name of the website
Here is what must happen:
• the Fully Qualified Domain Name portion of the URLs of the origin server’s content must contain the
advertised name of the website
• Media-IXT must answer to the advertised name of the website
In reverse proxy caching, because Media-IXT answers to the advertised name of the website, requests for
content on that origin server direct themselves to Media-IXT. There is no need to configure client browsers to
use the proxy cache. Nor do we need a layer 4 switch or WCCP2 router to intercept client requests and divert
them to the proxy cache.
In other words, neither explicit browser configuration nor a transparency device are needed. So a reverse proxy
cache is normally neither transparent nor explicit.
How do we insure that Media-IXT answers to the advertised name of the website? Of many possible ways to
do this, two approaches are described here.
Our examples:
• use Virtual IP Addressing, and
• assume that DNS resolves the advertised name of our website, www.somestreams.com, to a particular
IP address, 11.11.11.11.
One option is to configure Media-IXT to answer 11.11.11.11 as a Virtual IP Address (VIP).
Another is to configure a layer 4 switch with Network Address Translation (NAT) enabled, so that:
o the switch uses 11.11.11.11 as a Virtual IP Address, and
o the switch rewrites the destination IP address of packets sent to 11.11.11.11 with Media-IXT’s IP
address
These are among the techniques popular for reverse proxy deployments. See the HP Cache Server Appliance
Administrator Guide for more information about Virtual IP Addressing.
Reverse proxy caching and layer 4 switches in proxy mode
A layer 4 switch that uses NAT to rewrite IP addresses is in proxy mode (as opposed to providing transparency).
Often, a layer 4 switch in proxy mode performs load balancing between multiple Media-IXT reverse proxy
caches.
When the layer 4 switch is in proxy mode, there are two connections: one from the client to the switch, and
another from the switch to Media-IXT.
NOTE The descriptions of layer 4 switches in this manual make no pretense of being complete:
these switches’ capabilities are diverse, and evolving. This manual attempts to cover
only the aspects of layer 4 switches most relevant to proxy caching with Media-IXT.