Brocade Virtual ADX Server Load Balancing Guide (Supporting ADX v03.1.00) User Manual
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Brocade Virtual ADX Server Load Balancing Guide
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Layer 7 health checks
4
DNS
The Brocade Virtual ADX performs one or both of the following types of DNS health checks:
•
Address-based – The Brocade Virtual ADX sends an address request for a specific domain
name. If the server successfully responds with the IP address for the domain name, the server
passes the health check.
•
Zone-based – The Brocade Virtual ADX sends a Start-of-Authority (SOA) request for a specific
zone name. If the server is authoritative for the zone and successfully responds to the SOA
request, the server passes the health check.
NOTE
If you configure both types of DNS health check for a server, the server must successfully respond
to both health checks to remain in the server rotation. You enable each type of DNS health check on
a global basis and configure them on an individual server basis.
•
If the server replies with the requested IP address or zone name, the Brocade Virtual ADX
considers the server port to be ACTIVE and marks it as such.
•
If the server does not reply with the requested IP address or zone name, the Brocade Virtual
ADX retries the health check up to the number of times configured (the default is two retries). If
the server still does not send the requested information, the Brocade Virtual ADX marks the
DNS port on the server FAILED and removes the server from the rotation for DNS services.
NOTE
By default, the health check is non-recursive. If the real server (DNS server) does not successfully
reply to the health check, then the DNS port fails the health check. You can enable the real server
to perform a recursive lookup for the IP address or zone requested by the health check. In this case,
if the real server does not have the requested address or zone, the server can pass the request on
to a DNS server with higher authority. Refer to
“Enabling recursive DNS health checks”
Performed:
•
Immediately following a successful Layer 4 UDP health check
•
At regular intervals, if keepalive is enabled for the port
Configuration
To perform a health check on a DNS port, use a configuration such as the following.
Example
Virtual ADX(config-port-dns)#show run | b 53
server port 53
udp keepalive 15 3
tcp keepalive disable
server real rs1 10.2.2.200
port dns
port dns keepalive
port dns addr_query "www.brocade.com"
server virtual-name-or-ip test 10.2.2.222
sticky-age 60
port dns