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By default, the NetScaler has the ability to participate in Layer 3 routing i.e., learning and advertising routes using routing protocols such as Routing Information Protocol (RIP), Open Shortest Path First (OSPF) and Border Gateway Protocol (BGP). BGP is the de facto standard for routing IP traffic across the global Internet. It is a routing protocol designed to share IP network address groups, or prefixes, between multiple different organizations. Each of these organizations (usually an ISP or a large private network) classify their addressing space as an Autonomous System–a network, or group of networks, that has an addressing and routing structure unique from another organizations. BGP is a very complex and powerful routing protocol, which some characteristics that make it quite unique compared to other protocols like RIP or OSPF. All aspects of its configuration are done manually–there is no “auto-discovery” of neighboring routers. Connections to other BGP neighbors, once configured, use a TCP connection to exchange network prefixes. Because of the possibility of mistakenly sending or receiving route information that could bring down the routing tables for neighboring routers, or even the global Internet, there are many methods of screening and applying routing policies to updates sent or received from BGP peers.

A NetScaler can run BGP as a routing protocol to learn routes from other BGP routers, as well as advertise routes that the NetScaler knows about (networks downstream, vservers, and so on). Configuring NetScaler for BGP routing involves enabling dynamic routing, adding the BGP process to the routing engine, and configuring the BGP process with the essential BGP settings: peer router addresses and Autonomous System numbers, whether to redistribute routes from the kernel and/or defined static routes, and whether to learn routes from connected BGP peers. When a route is advertised, the BGP peers connected to the network, learns those routes. Frequent advertising of routes indicates that the peers are always kept aware of the routes in the network. If there are any errors that occur when a router advertises a route, then the availability of the router may alternate frwuently between up and down. Due to the instability of the router, the network topology is distorted which forces the routes to be withdrawn. If the instability continues, then the routes that are advertised will decrease and the routes that are withdrawn may subsequently go up resulting in high network latency. The Routing test helps administrators to keep a check on the number of routes that are advertised and the routes that are withdrawn over a period of time.

Using this test, administrators can figure out the routes that were advertised and the routes that were relearnt. In addition, this test will help administrators to identify the number of times the routes were withdrawn and the number of times the HA state of the routes was changed.

For this test to run and report metrics, the NetScaler device should be configured to create a Syslog file in a remote Syslog server, where the details of all interactions with the NetScaler appliance will be logged. To know how to configure the Syslog server where this Syslog file should be created, Click here.

Outputs of the test : One set of results for the NetScaler appliance being monitored

Measurement	Description	Measurement Unit	Interpretation
route_advertised	Indicates the number of routes advertised.	Number	A route advertisement is when a router, using a routing protocol such as RIP or EIGRP, sends information to another router indicating that a specific network is reachable, and what the next "hop" or IP address is to use to get to the final destination. A high value is desired for this measure. The detailed diagnosis of this measure if enabled lists the routes that were advertised.
route_withdrawn	Indicates the number of routes that were withdrawn.	Number	A route flap occurs when a router alternately advertises a destination network via one route then another, or when there’s an interface error on the router that alternates the availability of the router as up or down. When fluctuations are noticed repeatedly, the routing topology is distorted which in turn forces the router to withdraw the routes. Now, determining the next possible route will take longer than usual for the network thus leading to network latency or downtime. Therefore, the value of this measure should be kept at the least possible value. The detailed diagnosis of this measure if enabled, lists the routes that were withdrawn.
route_relearnt	Indicates the number of routes that were relearnt.	Number	The detailed diagnosis of this measure if enabled, lists the routes that were relearnt.
ha_state_changed	Indicates the number of times the HA state to the route was changed.	Number	The detailed diagnosis of this measure if enabled, lists the route for which the HA state changed.