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152 Chapter 4: Bridges/Switches and LAN Design
Figure 4-10
Broadcast Domains
General definitions for collision domain and broadcast domain are as follows:
A collision domain is a set of interface cards (NICs) for which a frame sent by one NIC
could result in a collision with a frame sent by any other NIC in the collision domain.
A broadcast domain is a set of NICs for which a broadcast frame sent by one NIC will be
received by all other NICs in the broadcast domain.
Layer 3 addressing is affected whenever a router is added to a network. For example, if only
bridges and switches had existed in the network in Figure 4-10, and if the router was later
added, Layer 3 IP and IPX addresses would have changed. To use the terminology in Chapter
3, two separate address groupings (for example, IP subnets) would be used for IP--one for the
devices to the left of the router and another for devices to the right of the router. A definition of
Layer 3 address groupings on LANs will help you understand VLANs better:
NOTE
All devices in the same broadcast domain (Layer 2) will be in the same Layer 3 address
grouping--in other words, the same IP subnet or same IPX network.
The internal processing on the switch can decrease latency for frames. Transparent bridges use
store-and-forward processing, meaning that the entire frame is received before the first bit of
ch04.fm Page 152 Monday, March 20, 2000 5:02 PM