Avaya P333R-LB Installation And Configuration Manual page 187

Web server.
3 The cache checks if it has the requested information. If it does, it replies to the
client. If the cache does not have the information, it retrieves the information
from the real Web server, and then replies to the client.
P333R-LB supports transparent caches. A transparent cache is capable of accepting
packets not destined to its IP. The cache usually uses NAT in its IP stack, so the
higher layers can process packets not destined to the cache IP.
The following steps illustrate an AR process:
1 The user issues an HTTP request with its IP address as the source address and
the Web server's IP address as the destination address.
2 P333R-LB routes the packet to the Web cache(s) (load balancing if needed), but
the packet still has the Web server's IP address as the destination IP address.
3 If the cache has the required page, the cache returns the page to the client with
the destination IP address of the client and the source IP address of the Web
server. If the cache does not have the required page, the cache returns the packet
to P333R-LB, and it is routed to the Web server.
4 On returning from the Web server, P333R-LB routes the packet to the cache. The
cache updates itself with the new page, and returns the packet to the client.
In the Cache Redirection packet flow, the following events need to be
indistinguishable on the IP level:
• Redirection of packets from the client to the cache.
• Routing of packets from the cache to the WAN.
To address this issue, P333R-LB uses different VLAN areas for the clients and the
cache. If a packet arrives to P333R-LB from the client's VLAN, it is redirected to the
cache, and if it arrives from the server's VLAN, it is routed to the WAN.
Avaya P333R-LB User's Guide
Chapter 14 Load Balancing in the P333R-LB
45