Application Content Verification

ACV Configured On a UDP Probe

UDP is a connectionless protocol. The UDP server must have a protocol capable of responding to a UDP ACV probe request, such as the UDP Echo protocol. In the case of the UDP Echo protocol, the response is an echo of the probe request sent to the server. In this case, the configured string of the expected reply from the server is the same as the configured request string.

ACV Configured On a TCP Probe

ACV works by sending a request to your application server and searching the response for a certain string. If it finds the string, the server is marked as Up. If the string is not found, the server is marked as Down.

For ACV verification of a TCP server application, you specify the following:

• A string that the router sends to the server. The string can be a simple HTTP command to get a specific HTML page, or it can be a command to execute a user-defined CGI script that tests the operation of the application.
• The reply that the application on each server sends back is used by the router to validate the content. In the case where a specific HTML page is retrieved, the reply can be a string that appears on the page, such as “OK”. If a CGI script is executed on the server, it should return a specific response (for example, “OK”) that the router can verify.

For example, if you sent the following string to your HTTP server, “HEAD / HTTP/1.1\\r\\nHost: www.extremenetworks.com\\r\\n\\r\\n”, you could expect to get a response of a string returned similar to the following:

HTTP/1.1 200 OK
Date: Tue, 9 Feb 2010 20:03:40 GMT
Server: Apache/2.0.40 (Red Hat Linux)
Last-Modified: Wed, 6 Jan 2010 13:56:03 GMT
ETag: “297bc-b52-65f942c0”
Accept-Ranges: bytes
Content-Length: 2898

You can search for a reply string of “200 OK”. This would result in a successful verification of the service.

Because ACV can search for a string in only the first 255 bytes of the response, in most HTTP cases the response will have to be in the packet's HTTP header (that is, you will not be able to search for a string contained in the web page itself).

Some protocols such as FTP or SMTP require users to issue a command to close the session after making the request. An ACV close string can be configured and sent by the Tracked Object Manager to the server to close the session.