Global Server Load Balancing overview | 1 |
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.
4. The GSLB ServerIron assesses each |
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| Authoritative DNS server | |||
IP address in the DNS reply to |
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| for domain brocade.com | |||
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determine the optimal site for the client, |
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| 209.157.23.46 | |||
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and moves the address for that site to |
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| DNS |
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the top of the list. |
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| GSLB ServerIron, proxy | |||
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| for the authoritative DNS | |
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| server for brocade.com | |
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| 209.157.23.87 | |||
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SI
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.
DNS
1. The client’s local DNS server sends a recursive query for brocade.com.
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.
GSLB Site 1
Sunnyvale
slb1: 209.157.22.209
SI
Router
SI
slb2: 209.157.22.210
GSLB Site 2
Atlanta
slb1: 192.108.22.111
SI
Router
SI
slb2: 192.108.22.112
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 “DNS cache proxy” on page 91 and “Transparent DNS query intercept” on page 95.
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
ServerIron ADX Global Server Load Balancing Guide | 5 |
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