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Chapter 1

The Campus Network

Broadcasts and Multicasts

Remember that all protocols have broadcasts built in as a feature, but some
protocols can really cause problems if not configured correctly. Some proto-
cols that, by default, can cause problems if not correctly implemented are
Internet Protocol (IP), Address Resolution Protocol (ARP), Network Basic
Input Output System (NetBIOS), Internetworking Packet eXchange (IPX),
Service Advertising Protocol (SAP), and Routing Information Protocol
(RIP). However, remember that there are features built into the Cisco router
Internetworking Operating System (IOS) that, if correctly designed and
implemented, can alleviate these problems. Packet filtering, queuing, and
choosing the correct routing protocols are some examples of how Cisco
routers can eliminate some broadcast problems.

Multicast traffic can also cause problems if not configured correctly. Multi-

casts are broadcasts that are destined for a specific or defined group of users.
If you have large multicast groups or a bandwidth-intensive application like
Cisco's IPTV application, multicast traffic can consume most of the network
bandwidth and resources.

To solve broadcast issues, create network segmentation with bridges,

routers, and switches. However, understand that you'll move the bottleneck
to the routers, which break up the broadcast domains. Routers process each
packet that is transmitted on the network, which can cause the bottleneck if
an enormous amount of traffic is generated.

Virtual LANs (VLANs) are a solution as well, but VLANs are just broad-

cast domains with boundaries created by routers. A VLAN is a group of
devices on different network segments defined as a broadcast domain by the
network administrator. The benefit of VLANs is that physical location is no
longer a factor for determining the port into which you would plug a device
into the network. You can plug a device into any switch port, and the net-
work administrator gives that port a VLAN assignment. Remember that
routers or layer 3 switches must be used for different VLANs to communicate.

The 80/20 Rule

The traditional campus network placed users and groups in the same phys-
ical location. If a new salesperson was hired, they had to sit in the same
physical location as the other sales personal and be connected to the

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