Cisco Systems RJ-45-to-AUX manual Broadcast and Unknown Server BUS, ATM Module Subinterfaces, 171

Broadcast and Unknown Server (BUS)

The BUS provides broadcasting support for an ELAN. The BUS distributes multicast data, sends or distributes unicast data, and connects the other LANE components. When the destination address of an Ethernet or Token Ring frame contains a local broadcast or a multicast address, the LEC forwards the traffic to the BUS, which forwards it to all the other LECs in the ELAN. At least one combined LES and BUS is required per ELAN. The BUS has the following functions:

∙Distributes multicast data

∙Sends or distributes unicast data

∙Interfaces to LEC and LES

The LES is the component responsible for resolving MAC addresses to ATM addresses, and the BUS is the component responsible for servicing multicast, Ethernet, and Token Ring broadcasts. The Cisco LANE implementation calls for the LES and the BUS to be configured in the same end−station.

ATM Module Subinterfaces

In order to configure ATM components on an ATM LANE module for the Catalyst 5000 or 6000 family of switches, you need to use subinterfaces. Depending on the level of traffic you expect on your network, you may want to place different LES/BUS components throughout the framework of your network. To configure a LES or BUS on the ATM module, you need to complete the following tasks:

1.Enter Interface Configuration mode.

2.Specify the subinterface for the ELAN.

3.Specify the type of link: Ethernet or Token Ring.

4.Enable the LES and BUS on the ELAN.

5.Repeat this process for each LES/BUS.

The BUS must be used to sequence and distribute broadcast data to all the LECs. However, sending a large volume of broadcast data to all the LECs can severely impact the overall performance of the network. For this reason, it may be necessary for the BUS to place restrictions on the LANE components to control the maximum throughput rate for each device. The BUS’s primary function is to provide broadcast management support for LANs. The BUS must supply the following services:

∙Distribute unicast and multicast data to all the LECs in the network

∙Connect interfaces to the ELAN

Distribution of unicast and multicast data includes the transmission of data to the LECs in the network. Whenever possible, the LEC will establish a direct connection to another LEC. If this isn’t possible, then data the BUS receives is broadcast to each LEC on the ELAN. This option can be enabled and disabled, and you should carefully consider whether you need this option, because it can eat up costly bandwidth.

Note When interfacing to ELANs, the BUS establishes a bi−directional connection that allows forwarding of multicast and unicast frames with unknown destinations.

LEC Queries

LECs send queries for configuration information to receive the LES address. The LECS then assigns the correct LES address for each LEC. The LES also has the ability to establish a connection with the LECS.

A reply to a query can be as simple as providing a single LES address or it can provide more information, such as:

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