UDP Health Monitor


This article covers the specific configuration for UDP health monitor type. Refer Overview of Health Monitors article for general monitor information, implementation, and other monitor types.

Send a UDP datagram to the server, then match the server’s response against the expected response data.

Configuring General Monitor

  • Send Interval — Frequency at which the health monitor initiates a server check in seconds.
  • Receive Timeout — Maximum amount of time before the server must return a valid response to the health monitor in seconds.
  • Successful Checks — Number of consecutive health checks that must succeed before Avi Vantage marks a down server as being back up.
  • Failed Checks — Number of consecutive health checks that must fail before Avi Vantage marks an up server as being down.

Note: Default System-UDP health monitor will detect failure only when ICMP unreachable is received. It will keep the server UP until it receives ICMP unreachable for the defined UDP port. Hence it does not detect the failure:

  • If the UDP health monitor request gets dropped or blackholed before reaching the server.
  • If ICMP unreachable response packets are being dropped.
  • If the backend UDP server does not send ICMP unreachable.

Configuring UDP Specific

  • Client Request Data — Specify an appropriate send string applicable for the server application.
  • Server Response Data — Specify the expected response from the server. Avi Vantage checks to see if the server response data is contained within the first 2KB of data returned from the server.
  • Health Monitor Port — Specify a port that should be used for the health check. When this setting is blank, the default port configured for the server will be used. When it is specified, clients may be directed to a different port than what is monitored.

Server Maintenance Mode

Custom server response can be used to mark a server as disabled. During this time, health checks will continue, and servers operate the same as if manually disabled, which means existing client flows are allow to continue, but new flows are sent to other available servers. Once a server stops responding with the maintenance string it will be brought online, being marked up or down as it normally would based on the server response data.

This feature allows an application owner to remove all connections from a server prior to taking the server offline without the requirement to log into Avi Vantage to first place the server in disabled state.

  • Maintenance Server Response Data — If the defined string is seen in the server response, place the server in maintenance mode.

Configuring NTP Health Checks

You can configure NTP health checks as follows:

1) Have a UDP health monitor with a request string and response string specified (this is the recommended option) as follows:

a) Request string — You can specify the request string as #000000000000000000000000000000000000000%NTPMON%.

b) Response string — You can specify the response string as NTPMON.

If you do not send any response, then the UDP health checks will fail with port-unreachable ICMP responses.