Layer 3 health checks utilize ICMP based echo requests (pings) to test whether a Real Server can be reached over the network. A Layer 3 check is not Virtual Service specific, for example, when it fails, the corresponding Real Server will be removed from all Virtual Services that use it.

In contrast to the Layer 3 health checks, service based health checking for both the Layer 4 and Layer 7 health checks are Virtual Service based. When a Real Server fails such a check, it will be removed only from the corresponding Virtual Service – all other Virtual Services that use this Real Server are unaffected.

Type

Description

ICMP

The LoadMaster sends ICMP echo requests (pings) to the Real Servers. A Real Server fails this check when it does not respond with an ICMP echo response in the configured response time for the configured number of retries.

TCP

The LoadMaster attempts to open TCP-connection to the Real Server on the configured service port: it sends a TCP SYN packet to the server on the service port. The server passes the check if it responds with a TCP SYN ACK in the response time interval. In this case the LoadMaster closes the connection by sending a TCP RESET. If the server fails to respond within the configured response time for the configured number of times, it is assumed dead.

FTP

The LoadMaster opens a TCP connection to the Real Server on the Service port (port 21). If the server responds with a greeting message with status code 220, the LoadMaster sends a QUIT command to the server, closes the connection and marks it as active. If the server fails to respond within the configured response time for the configured number of times, or if it responds with a different status code, it is assumed dead.

TELNET

The LoadMaster opens a TCP connection to the Real Server on the Service port (port 23). If the server responds with a command string beginning with the char ‘0xff’, the LoadMaster closes the connection and marks the server as active. If the server fails to respond within the configured response time for the configured number of times, or if it responds with a different command string, it is assumed dead.

SMTP

The LoadMaster opens a TCP connection to the Real Server on the Service port (port 25). If the server responds with a greeting message with status code 220, the LoadMaster sends a QUIT command to the server, closes the connection and marks it as active. If the server fails to respond within the configured response time for the configured number of times, or if it responds with a different status code, it is assumed dead.

HTTP

The LoadMaster opens a TCP connection to the Real Server on the Service port (port 80). The LoadMaster sends a HTTP/1.0 HEAD request the server, requesting the page “/”. If the server sends a HTTP response with a status code of 2 (200-299, 301, 302, 401) the LoadMaster closes the connection and marks the server as active. If the server fails to respond within the configured response time for the configured number of times, or if it responds with a different status code, it is assumed dead. HTTP 1.0 and 1.1 support available. HTTP 1.1 allows you to check host header enabled web servers.

HTTPS

The LoadMaster opens an SSL connection to the Real Server on the Service port (port 443). The LoadMaster sends a HTTP/1.0 HEAD request the server, requesting the page “/”. If the server sends a HTTP response with a status code of 2 (200-299, 301, 302, 401) the LoadMaster closes the connection and marks the server as active. If the server fails to respond within the configured response time for the configured number of times or if it responds with a different status code, it is assumed dead. HTTP 1.0 and 1.1 support available. HTTP 1.1 allows you to check host header enabled web servers.

POP3

The LoadMaster opens a TCP connection to the Real Server on the Service port (port 110). If the server responds with a greeting message that starts with +OK, the LoadMaster sends a QUIT command to the server, closes the connection and marks it as active. If the server fails to respond within the configured response time for the configured number of times, or if it responds with a different status code, it is assumed dead.

NNTP

The LoadMaster opens a TCP connection to the Real Server on the Service port (port 119). If the server responds with a greeting message with status code 200 or 201, the LoadMaster sends a QUIT command to the server, closes the connection and marks it as active. If the server fails to respond within the configured response time for the configured number of times, or if it responds with a different status code, it is assumed dead.

IMAP

The LoadMaster opens a TCP connection to the Real Server on the Service port (port 143). If the server responds with a greeting message that starts with “+ OK” or “* OK”, the LoadMaster sends a LOGOUT command to the server, closes the connection and marks it as active. If the server fails to respond within the configured response time for the configured number of times, or if it responds with a different status code, it is assumed dead.

DNS

The Name Server (DNS) Protocol value is only available in the Real Server Check Method drop-down list when the Virtual Service Protocol is set to udp. The LoadMaster performs nslookups against an A record on the server over UDP port 53. If the server successfully responds to the DNS query, the LoadMaster marks it as active. If the server fails to respond within the configured response time for the configured number of times or if it responds unsuccessfully to the A record, it is assumed down.

RDP

The LoadMaster sends an RDP Routing Token to the Real Server.

The RDP health check supports Network Level Authentication.

Binary

Specify a hexadecimal string to send to the Real Server. Specify a hexadecimal string which will be searched for in the response sent back from the Real Server. If the LoadMaster finds the pattern in the response, the Real Server is considered up. Specify the number of bytes to search for the reply pattern within.

LDAP

Select an LDAP endpoint to use for the health check. The LDAP health check uses the LDAP credentials and protocol specified in the LDAP endpoint. The health check is run against the Real Server IP address and port. The LDAP health check comprises of a LoadMaster connecting to a Real Server and validating the specified user credentials. The health check is performed in two steps:

Step 1: Check if the Real Server specified port is up and available.

Step 2: Attempt to log in to the Real Server using the LDAP specified credentials.

If step 1 and step 2 are true, the health check passes. If step 1 or step 2 fails, the health check fails.

None

No health checking is performed.