24
Chapter 4
Transparent Proxy Caching
Layer 4 switches offer the following features, depending on the particular switch:
•
A Layer 4 switch that can sense downed hosts on the network and redirect traffic adds reliability.
•
If a single Layer 4 switch feeds several Traffic Servers, the switch handles load balancing among the
Traffic Server nodes. Different switches might use different load balancing methods, such as round-robin
or hashing. If a Traffic Server node becomes unavailable, the switch automatically redistributes the load.
When the node returns to service, some switches automatically return the node to its previous workload,
so that the node cache need not be repopulated; this feature is called cache affinity. HP recommends that
you do not enable Traffic Server virtual IP failover in this situation, because Layer 4 switch failover is
already in operation.
Using a WCCP-enabled router for transparency
Traffic Server supports WCCP 1.0 and WCCP 2.0.
A WCCP 1.0-enabled router can send all port 80 (HTTP) traffic to Traffic Server, as shown in Figure 4-2.
below. The Traffic Server ARM readdresses port 80 to Traffic Server’s proxy port (by default, port 8080).
Traffic Server processes the request as usual, retrieving the requested document from the cache if it is a hit and
sending the response back to the client. Along the way, the ARM readdresses the proxy port in the response
header to port 80 (undoing the readdressing it did on the way to Traffic Server). The user then sees the response
exactly as if it were sent directly from the origin server.
A WCCP 2.0-enabled router works in the same way as a WCCP 1.0-enabled router. In addition to port 80
(HTTP) traffic, WCCP 2.0 supports additional protocols including NNTP (port 119 traffic).
Figure 4-2. Using a Cisco IOS router to send port 80 traffic to several Traffic Servers
end users
Traffic Server 1
internet
Cisco IOS router
switch or hub
Traffic Server 2
Traffic Server 3
80
all
all
