Group Policies

Advanced Switch Features

Figure 7-8. Advanced Switch Features Page

The problem of broadcast control is addressed in part by the use of two features, Automatic Broadcast Control (ABC) and Internet Group Management Protocol (IGMP).

Automatic Broadcast Control (ABC)

Automatic Broadcast Control (ABC) is a feature that controls broadcasts through IP/IPX Broadcast Reduction. IP/IPX Broadcast Reduction reduces the number of broadcasts propagated through the network.

Using ABC, the switch acts as a proxy server, replying to Address Resolution Protocol (ARP) requests, Nearest Server Query (NSQ) requests, and GetLocalTarget requests on behalf of the destination node. An ARP cache (learned address table) is created for each subnet allowing the switch to proxy reply with the resolved MAC address instead of forwarding the requests out all ports. This limits the broadcasts within the switching domain. The Service Advertising Protocol (SAP) table performs the same function in an IPX network. By using these tables, the switch can resolve addresses for any node in the network that it already knows about.

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