HP J3250M manual Configuration Device Features, Automatic Broadcast Control ABC

Managing Switches

Managing Switches

Configuration

VLANs make large networks more manageable. You can group users according to some shared characteristic, such as a common business function or a common protocol. A single switch may have several independent VLANs within it.

Note: VLANs must be created with the device console.

Configuration - Device Features

The Device Features page (only found on switches) lets you set some or all of these features:

■Automatic Broadcast Control (ABC)

■Multicast Filtering (IGMP)

■Spanning Tree

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.

Routing Information Protocol. The switch also intercepts Routing Information Protocol (RIP) and SAP broadcasts and forwards these only to ports where routers and servers have been detected. This also reduces the number of broadcasts on the network.

For example, if User A sends out a broadcast message to connect to its server, the request is sent out of all ports on the switch. When the server responds to User A, the switch intercepts the response and learns that the server is on that port. When User B sends a request to the same server, the switch already knows which port that server is on and sends that information to User B, just as if the server had responded to the request. User B’s request is not broadcast out any of the switch ports.

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