Networking Concepts Review - CCIE Routing and Switching Exam Certification Guide - page 35

Bridges Control Collision Domains Figure 2-6

Bridges

Collision Domains

Broadcast Domain

Switches use fast integrated circuits that reduce the latency common to regular bridges.
Switches are the evolution of bridges. Some switches have the capability to run in cut-through
mode where the switch does not wait for the entire frame to enter its buffer; instead, it begins
to forward the frame as soon as it finishes reading the destination MAC address. Cut-through
operation increases the probability that error frames are propagated on the network because the
frame is forwarded before the entire frame is buffered and checked for errors. Because of these
problems, most switches today perform store-and-forward operations as bridges do. Switches
are exactly the same as bridges with respect to collision domain and broadcast domain
characteristics. Each port on a switch is a separate collision domain. All ports in a switch are in
the same broadcast domain.

Various types of bridges exist, including transparent, translational, source-route, and so on.
These bridging types are covered in Chapter 4.

Routers and Layer-3 Switches
Routers operate in the network layer of the OSI model. They make forwarding decisions based
on network layer addresses (e.g., an IP address). Figure 2-7 shows that routers define both colli-
sion (bandwidth) and broadcast domains. Each router interface is a separate broadcast domain
that is defined by a separate sub-network. Routers are protocol aware, which means that they are
capable of forwarding packets of routable protocols such as IP, IPX, DECnet, and AppleTalk.

Figure 2-7

Routers Define Collision and Broadcast Domains

Routers

Collision and broadcast
domains