Nortel Networks WEB OS 212777 - Manual (Page 317)

Web OS 10.0 Application Guide
Chapter 13: Firewall Load Balancing n 317
212777-A, February 2002
Basic FWLB Implementation
In this example, traffic is load balanced among the available firewalls.
Figure 13-3 Basic FWLB Process
1. The client requests data.
The external clients intend to connect to services at the publicly advertised IP address assigned
to a virtual server on the clean-side Web switch.
2. A redirection filter balances incoming requests among different IP addresses.
When the client request arrives at the dirty-side Web switch, a filter redirects it to a real server
group that consists of a number of different IP addresses. This redirection filter splits the traffic
into balanced streams: one for each IP address in the real server group. For FWLB, each IP
address in the real server group represents an IP Interface (IF) on a different subnet on the
clean-side Web switch.
3. Requests are routed to the firewalls.
On the dirty-side switch, one static route is needed for each traffic stream. For instance, the first
static route will lead to an IP interface on the clean-side Web switch using the first firewall as
the next hop. A second static route will lead to a second clean-side IP interface using the second
firewall as the next hop, and so on. By combining the redirection filter and static routes, traffic
is load balanced among all active firewalls.
All traffic between specific IP source/destination address pairs flows through the same fire-
wall, ensuring that sessions established by the firewalls persist for their duration.
N OTE – More than one stream can be routed though a particular firewall. You can weight the
load to favor one firewall by increasing the number of static routes that traverse it.
"Dirty" Side "Clean" Side
Internet
Firewalls
Servers
Web Switch
Client
Web Switch
3
4
5
8
7
6
1 2
9
10
1. Client sends a request
2. Redir filter selects upper or lower path
3. Static route directs request through
the selected firewall
4. Firewall forwards valid traffic
5. SLB selects an available server
6. Server responds
7. Redir filter selects reverse path
8. Static route directs response back
through the same firewall
9. Firewall forwards valid traffic
10. Client receives response