Different Health Checking Methods

Layer 3 health checks utilize ICMP-based echo requests (pings) to test if 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 a 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 LoadMaster sends Source-of-Authority (SOA) request to the Real Server on the service port (port 53 UDP). If the server successfully responds to the SOA request, 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 SOA request, it is assumed dead.

RDP

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

The RDP health check supports Network Level Authentication.

None

No health checking is performed.

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david.zaring

Which interface performs the health check?

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Nurul Kaium

It will be the interface local to individual server. If you do not have an interface local to server, loadmaster will use the interface where default gateway is on.