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ServerIron ADX Global Server Load Balancing Guide 85
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Affinity
1
Affinity
The GSLB affinity feature configures the GSLB ServerIron ADX to always prefer a specific site
ServerIron ADX for queries from clients whose addresses are within a given IP prefix. This feature is
useful in the following situations:
• When you want to use a primary site for all queries and use other sites only as backups.
• When you want to use a site located near clients within a private network for all queries from
the private network.
To configure affinity, you associate a site ServerIron ADX with an IP prefix. When the GSLB
ServerIron ADX receives a query from a client whose IP address is within the configured prefix, the
GSLB ServerIron ADX examines the DNS reply for a virtual IP address (VIP) configured on the
ServerIron ADX associated with the IP prefix that contains the client’s IP address.
Figure 5 shows an example of the affinity feature. In this example, the GSLB ServerIron ADX
contains the following affinity configuration:
• IP prefix: 192.0.0.0/8, site ServerIron ADX: 209.157.22.209 (slb1 in the sunnyvale site)
FIGURE 5 Example of the affinity feature
In Figure 5, the client’s IP address is within the configured affinity prefix, so the ServerIron ADX
checks the DNS reply for a VIP configured on the ServerIron ADX associated with the prefix:
1. The client’s local DNS
server sends a recursive
query for brocade.com.
DNS
DNS Client
192.108.1.100
2. The GSLB ServerIron forwards
the lookup request to the
authoritative DNS server.
4. The GSLB ServerIron checks for
an affinity configuration that has an
IP prefix that contains the client’s IP
address.
If one exists, and if the DNS reply
contains a VIP configured on the
ServerIron associated with the IP
prefix, the ServerIron checks the
health of the VIP.
If the VIP passes the health checks,
the ServerIron places the VIP at the
top of the list in the DNS reply.
DNS
3. The authoritative DNS server for
brocade.com answers the client’s
query by sending a list of IP
addresses for the sites that
correspond to the requested host.
SI
5. The client receives a reordered list
of IP addresses. The address at the
top of the list is a VIP on the
ServerIron associated with the IP
prefix that contains the client’s IP
address.
Authoritative DNS server
for domain brocade.com
209.157.23.46
GSLB ServerIron, proxy
for the authoritative DNS
server for brocade.com
209.157.23.87
Router
SI
SI
slb2: 209.157.22.210
slb1: 209.157.22.209
VIP: 209.157.22.69
GSLB Site 1
Sunnyvale
SI
SI
Router
slb2: 192.108.22.112
slb1: 192.108.22.111
GSLB Site 2
Atlanta