Section 10-3. SLB Probes


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

1.

Define the probe:

IOS

 (global) ip slb probe name {ping | http | wsp} 

CSM

[View full width]

 (csm) probe probe-name {http | icmp | telnet | tcp  | ftp | smtp | dns} 


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). In addition, the CSM allows http, icmp (Ping), telnet, tcp (TCP connection), ftp, smtp, and dns.

2.

(Optional) Define the target address:

IOS

 (probe) address [ip-address] 

CSM

 (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. However, a CSM allows an address to be configured for a ping or DNS probe type.

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.

3.

Set the probe behavior:

a. (Optional) Set the time between probes:

IOS

 (probe) interval seconds 

CSM

 (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; CSM only) Set the time to wait for a non-TCP probe reply:

IOS

N/A

CSM

 (probe) receive receive-timeout 


The CSM waits receive-timeout (1 to 65,535 seconds; default 10 seconds) for data to be received in response to probes other than TCP.

c. (Optional; CSM only) Set the time to wait for a TCP probe connection:

IOS

N/A

CSM

 (probe) open open-timeout 


For HTTP, TCP, FTP, Telnet, and SMTP probes, the CSM waits open-timeout (1 to 65,535 seconds; default 10 seconds) for a TCP connection to be opened in response to the probe.

d. (Optional) Define the criteria for a failure:

IOS

 (probe) faildetect retry-count 

CSM

 (probe) retries 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.

e. (Optional; CSM only) Wait to retry a failed server:

IOS

N/A

CSM

 (probe) failed failed-interval 


When a CSM has determined that a server has failed, it waits failed-interval (5 to 65,535 seconds; default 300 seconds) before sending another probe.

4.

(Optional; HTTP probe only) Define the HTTP probe operation:

a. (Optional; IOS SLB only) Set the port number:

IOS

 (probe) port port-number 

CSM

N/A


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 be able to answer an HTTP request for the probe to work.

b. (Optional) Define the HTTP probe method:

IOS

[View full width]

 (probe) request [method {get | post | head | name  name}] [url path] 

CSM

 (probe) request [method {get | head}] [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 /).

c. (Optional) Specify the probe header information:

IOS

 (probe) header field-name [field-value] 

CSM

 (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 

d. (Optional) Specify the HTTP authentication values:

IOS

 (probe) credentials username [password] 

CSM

 (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.

e. (Optional) Expect a specific status code to be returned:

IOS

[View full width]

 (probe) expect [status status-code] [regex  regular-expression] 

CSM

 (probe) expect status min-number [max-number] 


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.

5.

(Optional; WSP probe only) Define the target URL:

IOS

 (probe) url [path] 

CSM

N/A


A URL can also be given, specifying the server path (text string URL; default /).

6.

(Optional; DNS probe only) Define the domain name:

IOS

N/A

CSM

 (probe) name domain-name 


A DNS probe requires a domain-name (text string) that can be resolved by a DNS server target.

Displaying Information About SLB Probes

Table 10-3 lists some switch commands that you can use to display helpful information about SLB probes.

Table 10-3. Commands to Display SLB Probe Information

Display Function

Switch OS

Command

Probe configuration and status

IOS

 (exec) show ip slb probe [name probe_name] [detail] 

CSM

[View full width]

 (exec) show module csm slot probe [http | icmp |  telnet | tcp | ftp | smtp | dns] [name probe_name]  [detail] 




Cisco Field Manual. Catalyst Switch Configuration
Cisco Field Manual. Catalyst Switch Configuration
ISBN: 1587050439
EAN: N/A
Year: 2001
Pages: 150

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