Chapter 10: Server Load Balancing (SLB) 165
Section 10-3
■ FTP: Opens and closes an FTP connection (TCP ports 20 and 21) to a real server.
■ SMTP: Opens and closes an SMTP connection (TCP port 25) to a real server.
■ DNS: Sends requests to and verifies the replies from a real DNS server.
Configuration
1. Define the probe:
(global) ip slb probe name {ping | http | wsp}
The probe is named name (text string up to 15 characters) and can be referenced by
other SLB server and firewall farm commands. IOS SLB allows these probe types:
ping (ICMP), http, or wsp (WAP port 9201). (Optional) Define the target address:
(probe) address [ip-address]
For a server farm, this command is not used. The ip-address used by the probe is
inherited from each real server in the server farm. With IOS SLB, addresses are not
inherited when the probe is used for a firewall farm. You must use this command to
define the address of a target firewall.
2. Set the probe behavior:
a. (Optional) Set the time between probes:
(probe) interval seconds
Probes are sent toward the target at intervals of seconds (IOS SLB: 1 to 65,535
seconds; default 1 second; CSM: 5 to 65,535 seconds; default 120 seconds).
b. (Optional) Define the criteria for a failure:
(probe) faildetect retry-count
With IOS SLB, a server or firewall is considered to have failed if retry-count (1
to 255; default 10) consecutive ping probes are unanswered. With a CSM, the
target has failed if retry-count (0 to 65,535; default 3) probes of any type are
unanswered.
3. (Optional; HTTP probe only) Define the HTTP probe operation:
a. (Optional) Set the port number:
(probe) port port-number
Usually, an HTTP probe uses port-number 80. If the port-number is unspeci-
fied, however, it is inherited from the virtual server. For a firewall probe, the
port-number must be given (1 to 65,535). The target device must answer an
HTTP request for the probe to work.
b. (Optional) Define the HTTP probe method:
(probe) request [method {get | post | head | name name}] [url path]
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