Brocade Communications Systems 12.4.00 Manual De Usuario
ServerIron ADX Global Server Load Balancing Guide
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Global Server Load Balancing overview
1
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.
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
and either redirect or directly respond to DNS queries. Refer to
on page 91 and
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
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
1. The client’s local DNS
server sends a recursive
query for brocade.com.
server sends a recursive
query for brocade.com.
DNS
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.
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 server by the virtual IP address
configured on the GSLB ServerIron,
instead of its real IP address.
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.
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.
DNS
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.
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.
SI
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.
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.
Authoritative DNS server
for domain brocade.com
for domain brocade.com
209.157.23.46
GSLB ServerIron, proxy
for the authoritative DNS
server for brocade.com
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
GSLB Site 1
Sunnyvale
Sunnyvale
SI
SI
Router
slb2: 192.108.22.112
slb1: 192.108.22.111
GSLB Site 2
Atlanta
Atlanta