Brocade Virtual ADX Server Load Balancing Guide (Supporting ADX v03.1.00) - Manual (Page 180)

164 Brocade Virtual ADX Server Load Balancing Guide
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Layer 4 health checks
4
Server response threshold health check
The Brocade Virtual ADX distributes traffic among real servers based on a dynamic weight value
derived from the caculated response time of health check packets. Using the same calculated
response times, the Brocade Virtual ADX can perform Layer 4 and Layer 7 health checks.
The Brocade Virtual ADX calculate Layer 4 and Layer 7 response times and compares those with
the configured response threshold. If the calculated response time is greater than the configured
response threshold, the port is marked DOWN.
The Brocade Virtual ADX calculates Layer 4 and Layer 7 response times differently:
• Layer 4 response times (round trip times) measure the time between the sending of a SYN
packet and receiving a SYN ACK packet.
• Layer 7 response times measure the time between the L7 request and the first response
packet returned to the server. In the case of an LDAP server, this is the time between a bind
request and bind reply. For HTTP servers, this is the time between sending a GET or HEAD
request and the first packet received from server.
The calculated response time is compared to a user-configured response threshold. You can
configure a Layer 4 response threshold, a Layer 7 response threshold, or a combined Layer 4 and
Layer 7 response threshold.
To define the server response threshold, enter commands such as the following.
Virtual ADX(config)#server real r1 192.168.20.43
Virtual ADX(config-rs-r1)#port http response-threshold layer4 200
Virtual ADX(config-rs-r1)#port http response-threshold layer7 800
Syntax: [no] response-threshold {layer4 | layer7 | layer4&7} threshold-value
The layer4 keyword specifies a Layer 4 response threshold. The layer7 keyword specifies a Layer 7
response threshold. The layer4&7 keyword specifies combined Layer 4 and 7 response threshold.
The threshold-value variable is the server response threshold in microseconds. Enter an integer
from 1 to 50,000.
Debugging and testing
The show server real command displays health check counters for the port and all servers which
you can use when you test or debug response threshold health checks.
Syntax: show real server portnum | port-name