Objective Area #4: Technology

Under this final heading you'll find these topics listed:

• Describe network communications using layered models.
• Describe the Spanning Tree process.
• Compare and contrast key characteristics of LAN environments.
• Evaluate the characteristics of routing protocols.
• Evaluate TCP/IP communication process and its associated protocols.
• Describe the components of network devices.
• Evaluate rules for packet control.
• Evaluate key characteristics of WANs.

Spanning tree protocol (STP) is enabled by default on all Cisco switches. Along with STA (Spanning Tree Algorithm), it avoids switched network loops. STP allows exchange of bridge protocol data units (BPDUs) by the switches to choose a Root bridge (switch, in this case) and determine where the network loops are present. Then the STA requires switches responsible for creating loops place their redundant port or ports in a blocked state preventing network loops. There are five port states possible: blocking, listening, learning, forwarding and disabled.

Tip: The listening state is where the port determines whether or not it should participate in the forwarding of frames. The learning state is when the port learns MAC addresses that are added to the forwarding database.

Remember, routers divide networks into different broadcast domains for controlling client and server network broadcast traffic. Switches and bridges create or divide collision domains.

HDLC is the default Cisco router serial interface encapsulation type and is only understood by other Cisco routers using Cisco's HDLC.

Tip: ISDN supports a faster call setup than traditional analog modems.

PPP is an authentication method; using chap is preferred since the password is never sent across the wire. The configuration command is username username password password, where username is the hostname of the peer router. Note: passwords must be identical at both ends and the hostname and password are case sensitive.