Foundry Networks Switch and Router Installation And Configuration Manual page 233

For details on UDP helper and its configuration, see "Configuring UDP Broadcast and IP Helper Parameters" on
page 15-70.
NOTE: UDP Helper is supported only on Foundry routers. To configure a Foundry Layer 2 Switch or a
ServerIron to help BootP/DHCP packets, use the DHCP Assist feature. See "Configuring DHCP Assist" on
page 15-79.
Layer 4 Switching Features
The following sections describe the Layer 4 switching features listed in Table 8.1 on page 8-2. Foundry devices
support the following Layer 4 features:
• Session switching, on the ServerIron and Layer 2 Switches upgraded with Transparent Cache Switching
(TCS) and Server Load Balancing (SLB) software
• Session filters
These features enable you to take advantage of performance and reliability features such as selectable Quality of
Service (QoS), described in "IronClad Quality of Service (QoS)" on page 11-1.
Session Switching
The ServerIron and Layer 2 Switches upgraded with SLB or TCS software support switching of Layer 4 sessions.
A session is a traffic flow consisting of source and destination IP addresses and UDP or TCP port numbers. UDP
and TCP port numbers generally are associated with specific IP applications. Thus, a session represents a
specific traffic flow and the application in use on that flow.
The TCS and SLB features enable the ServerIron or upgraded Layer 2 Switch to load balance Layer 4 traffic
among multiple servers and automatically redirect traffic to other servers if a server fails. TCS and SLB are
described in more detail later in this chapter.
TCP/UDP Access Policies
TCP/UDP access policies (sometimes called session filters) allow you to filter packets for specific Layer 4
sessions. For example, you can use session filters to prohibit specific users from using TCP port 80 (HTTP for
web traffic). All Foundry devices support TCP/UDP access policies. For syntax information, see "TCP/UDP
Access Policies" on page C-20.
Layer 4 Caching Features
The following sections describe the ServerIron's Layer 4 caching features listed in Table 8.1 on page 8-2. For
additional information, see the Foundry ServerIron Installation and Configuration Guide.
The caching features are standard on ServerIron switches. In addition, you can upgrade a FastIron Backbone
Switch or Stackable TurboIron Layer 2 Switch (not the TurboIron/8) with these caching features.
Transparent Cache Switching (TCS)
Transparent Cache Switching (TCS) allows a ServerIron to detect and switch web traffic to a local cache server
within the network. Foundry Layer 2 Switches with TCS support can provide transparent cache switching for up to
1,024 web cache servers.
TCS eliminates the need to individually configure caching mechanisms in users' web browsers. Instead, the
ServerIron or backbone Layer 2 Switch "transparently" performs the caching on behalf of the user.
TCS Policy Filters
When you configure TCS, all packets addressed to TCP port 80 (HTTP) are diverted to web cache servers by
default. If you want web traffic for some IP sub-nets or specific IP addresses to bypass the caches and go directly
December 2000
Software Overview
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