10-3: SLB Probes
- Probes can be used to test for server or firewall connectivity and proper operation.
Probes can be defined to simulate requests for these protocols:
- ICMP: Sends ICMP echo (ping) requests to a real server.
- HTTP: Sends HTTP requests to a real server, using TCP port 80.
- WSP: Requests and verifies the replies using Wireless Access Protocol (WAP), port 9201.
- Telnet: Opens and closes a Telnet connection (TCP port 23) to a real server.
- TCP: Establishes and resets TCP connections to a real server. This can be used to support any TCP port, including HTTPS or SSL, port 443.
- 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
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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.
Set the probe behavior:
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(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).
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(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.
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(Optional; HTTP probe only) Define the HTTP probe operation:
(Optional) Set the port number:
(probe) port port-number
Usually, an HTTP probe uses port-number 80. If the port-number is unspecified, 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.
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(Optional) Define the HTTP probe method:
(probe) request [method {get | post | head | name name}] [url path]The probe requests information from the server using the get (the default), post, head (request a header data type), or name (request the data named name) method. A URL can also be given, specifying the server path (text string URL; default /).
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(Optional) Specify the probe header information:
(probe) header field-name [field-value]
The probe header name is set to field-name (text string up to 15 characters), with a value of field-value. A colon is automatically inserted between the name and value. By default, the request contains these headers:
Accept: */* Connection: close User-Agent: cisco-slb-probe/1.0 Host: virtual-IP-address
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(Optional) Specify the HTTP authentication values:
(probe) credentials username [password]
If HTTP authentication is required, a username (text string, up to 15 characters) and a password (text string up to 15 characters) can be given for the probe.
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(Optional) Expect a specific status code to be returned:
(probe) expect [status status-code] [regex regular-expression]
A real server or a firewall is considered to have failed if it either does not respond to an HTTP probe or if it returns a status-code (100 to 599, default 200) other than the one specified. For firewalls, the status-code should be set to 401. For a CSM, the status code must be within the range min-number (default 0) and max-number (optional, default 999).
With IOS SLB, you can also expect a regular expression along with the status code. Use the regex keyword and specify a regular-expression (text string, no default). Only the first 2920 bytes of the probe reply are searched for a match.
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(Optional; WSP probe only) Define the target URL:
(probe) url [path]
A URL can also be given, specifying the server path (text string URL; default /).
Displaying Information About SLB Probes
To display helpful configuration and status information about SLB probes, enter the following command:
(exec) show ip slb probe [name probe_name] [detail]