Brocade Communications Systems ServerIron ADX 12.4.00 Manual Manual page 17

4. The GSLB ServerIron assesses each
IP address in the DNS reply to
determine the optimal site for the client,
and moves the address for that site to
the top of the list.
2. The GSLB ServerIron, as proxy for the
authoritative DNS server, forwards the
lookup request from the client's local DNS
server to the authoritative DNS server.
Other DNS servers know the authoritatitve
DNS server by the virtual IP address
configured on the GSLB ServerIron,
instead of its real IP address.
1. The client's local DNS
server sends a recursive
query for brocade.com.
This example shows a ServerIron ADX configured as a DNS proxy. The ServerIron ADX is configured
as a DNS proxy for the DNS server that is authoritative for the domain brocade.com. To configure
the ServerIron ADX as a DNS proxy, you identify the DNS name and configure a virtual IP address
(VIP) for the DNS. Requests from clients or other DNS servers go to the VIP on the ServerIron ADX,
not directly to the DNS server. The ServerIron ADX then sends the requests to the DNS server,
transparently to the clients or other DNS servers.
NOTE
As an alternative to configuring the GSLB ServerIron ADX as a proxy, you can configure it to intercept
and either redirect or directly respond to DNS queries. Refer to
"Transparent DNS query intercept"
The client's local DNS server might cache DNS replies from the authoritative server. Normally,
these cached responses would prevent the global SLB from taking place, since the local DNS
server would respond directly to the client without sending a recursive query to the authoritative
DNS server. However, the GSLB ServerIron ADX, as a proxy for the authoritative DNS server,
automatically resets the Time-to-Live (TTL) parameter in each DNS record from the authoritative
server. By default, the GSLB ServerIron ADX sets the TTL to 10 seconds. As a result, other DNS
ServerIron ADX Global Server Load Balancing Guide
53-1002437-01
3. The authoritative DNS server for
brocade.com answers the client's query
(forwarded by the GSLB ServerIron) by
sending a list of IP addresses for the sites
that correspond to the requested host.
Authoritative DNS server
for domain brocade.com
209.157.23.46
DNS
GSLB ServerIron, proxy
for the authoritative DNS
server for brocade.com
209.157.23.87
SI
DNS
5. The client receives a reordered list
of IP addresses. Typical clients use
the first address in the list. Since the
ServerIron has optimized the list for
the client, the first address is the
best address.
on page 95.
Global Server Load Balancing overview
GSLB Site 1
Sunnyvale
slb1: 209.157.22.209
Router
slb2: 209.157.22.210
GSLB Site 2
Atlanta
slb1: 192.108.22.111
Router
slb2: 192.108.22.112
"DNS cache proxy"
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