Overview of User Datagram Protocol Load Balancing on a NetScaler Appliance
Article ID: CTX110551
Updated On:
Description
This article contains information about the basic functionality of the User Datagram Protocol (UDP) load balancing in a NetScaler appliance.
Background
TCP is a connection-oriented and reliable protocol that uses sequence numbers to track the transmission and receipt of data. The mechanisms used for tracking data transfer ensure that data is successfully transmitted and received. However, UDP is a connectionless and unreliable protocol. Using this protocol, data is sent from one computer to another using an IP address and a port number, assuming that the data is received correctly.
Overview of UDP Load Balancing
The TCP protocol uses certain methods to establish a connection between devices and monitors the transmission and receipt of data. These methods include connection sequence numbering and receipt acknowledgment. These methods allow the NetScaler appliance to track TCP connections and load balance the requests to back end servers, optimally. The appliance creates a table that contains details of the connections and the back end servers to which the requests are sent.
However, the UDP protocol does not use connection sequence numbering. Therefore, it is difficult to confirm the successful transmission and receipt of data packets from one device to another. As a result, the only way a NetScaler appliance can track UDP connections is through the source and destination addresses and the port numbers. This method does not help in determining the connection to which the data packets belongs. This situation causes a problem in load balancing because the appliance cannot track details about the connection and the back end server to which the request is sent.
The following steps detail the solution to this problem:
-
On the first connection, forcibly load balance data transfer between a source address or port number, and a destination address or port number to a physical server.
-
Enforce a persistent connection to the same physical server for a defined duration.
This can be achieved by setting persistent timeout value under Load Balancing > Virtual Server > Method and Persistence.
For protocol type UDP the following persistence methods are available.
Examples of UDP-based traffic include Domain Name System (DNS) address lookups and Network Time Protocol (NTP), both of which exist for a very short time. Generally, UDP connections exist for a very short duration. Therefore, time-based load balancing does not create any issues.
Issue/Introduction
