Figure 6-5 – Nortel Networks WEB OS 212777 User Manual
Page 123
Web OS 10.0 Application Guide
Chapter 6: Server Load Balancing
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123
212777-A, February 2002
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Some services require that a series of client requests go to the same real server so that ses-
sion-specific state data can be retained between connections. Services of this nature
include Web search results, multi-page forms that the user fills in, or custom Web-based
applications typically created using
cgi-bin
scripts. Connections for these types of ser-
vices must be configured as persistent (see
) or must use the
minmisses
or
hash
metrics (see
“Metrics for Real Server Groups” on page 131
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Clients and servers can be connected through the same switch port. Each port in use on the
switch can be configured to process client requests, server traffic, or both. You can enable
or disable processing on a port independently for each type of Layer 4 traffic.
o
Layer 4 client processing: Ports that are configured to process client request traffic
provide address translation from the virtual server IP to the real server IP address.
o
Layer 4 server processing: Ports that are configured to process server responses to cli-
ent requests provide address translation from the real server IP address to the virtual
server IP address. These ports require real servers to be connected to the Web switch
directly or through a hub, router, or another switch.
N
OTE
–
Switch ports configured for Layer 4 client/server processing can simultaneously pro-
vide Layer 2 switching and IP routing functions.
Consider the following network topology:
Figure 6-5 Example Network for Client/Server Port Configuration
In
, the switch load balances traffic to a Web server pool and to a Domain Name
System (DNS) server pool. The switch port connected to the Web server pool (port 2) is
asked to perform both server and client processing.
Some topologies require special configuration. For example, if clients were added to Switch B
as shown in
, these clients could not access the Web server pool using SLB services,
except through a proxy IP address that is configured on port 2 of the Alteon Web switch.
Web Switch
Router
DNS
Server
Pool
Web
Server
Pool
Internet
C
S
Client Processing
Server Processing
S
C
Clients on the Internet
initiate HTTP sessions which
are load balanced to Web servers
Web servers initiate DNS requests
which are load balanced
to DNS servers
S
C
A
B
1
2
3