Foundry Networks Switch and Router Installation And Configuration Manual page 985

Chapter 26
Route Health Injection
You can configure a Foundry Layer 3 Switch to check the health of the HTTP application and "inject" a host route
into the network to force a preferred route to an actively responding web host. The web host can be directly
attached to the Layer 3 Switch or can be attached through Layer 2 Switches. The web host can be a web server
or a Foundry ServerIron or third-party Server Load Balancing (SLB) device configured with a virtual IP address
(VIP) representing the HTTP application.
NOTE: This feature is supported on the Chassis Layer 3 Switches, the TurboIron/8 Layer 3 Switch, and the
NetIron Stackable Layer 3 Switch.
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The route health injection feature enables a router to advertise a host route to a globally-distributed web site.
Gateway routers that receive the host route along with other routes to the same web site in other locations can
choose the best route. Web clients attached to the gateway servers thus enjoy fast response time regardless of
their location, because their gateway routers use the best path to the web site. By advertising the host route
instead of a network route to the web site's IP address, the Foundry Layer 3 Switch ensures that gateway routers
receive a route to the IP address only if that IP address is available. The Foundry Layer 3 Switch uses a Layer-4
HTTP health check that you configure to determine whether the HTTP (web) service on the IP address is
available. The health check and how to configure it are described later in this section.
NOTE: This feature supports health checks only for TCP port 80 (HTTP).
Normally, an IP address should exist on only one host on the public Internet. However, the Foundry ServerIron
and some third-party SLBs allow the same IP address to exist on multiple machines using virtual IP addresses
(VIPs). A VIP is an IP address that you configure on a ServerIron or third-party SLB, then associate with "real"
servers attached to the ServerIron. These real servers are the web hosts that contain the web site requested by
clients. In a simple SLB configuration, a single ServerIron contains a VIP that maps to multiple real servers that
have identical contents. The VIP is the IP address associated with the web site on DNS servers. In a globally-
distributed SLB configuration, multiple ServerIrons or other SLBs in different networks throughout the Internet are
configured with same VIP and are attached to sets of real servers that contain the web site's content.
NOTE: Host-route support for globally-distributed SLB applies only to Foundry Layer 3 Switches. You can use
the feature regardless of whether the Layer 3 Switch is directly attached to a web server that contains the web site
or is attached to ServerIrons or third-party SLBs that load balance the IP address for the servers. Where this
feature description discusses the ServerIron, the description also applies to third-party SLB products with
comparable support for virtual IP addresses (VIPs).
1.This feature is also known as Global IP.
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