22 Chapter 1: Ethernet Basics
Foundation Summary
This section lists additional details and facts to round out the coverage of the topics in this chapter.
Unlike most of the Cisco Press Exam Certification Guides, this “Foundation Summary” does not
repeat information presented in the “Foundation Topics” section of the chapter. Please take the
time to read and study the details in the “Foundation Topics” section of the chapter, as well as
review items noted with a Key Topic icon.
Table 1-8 lists the different types of Ethernet and some distinguishing characteristics of each type.
Table 1-8 Ethernet Standards
Switches forward frames when necessary, and do not forward when there is no need to do so, thus
reducing overhead. To accomplish this, switches perform three actions:
■ Learn MAC addresses by examining the source MAC address of each received frame
■ Decide when to forward a frame or when to filter (not forward) a frame, based on the
destination MAC address
■ Create a loop-free environment with other bridges by using the Spanning Tree Protocol
Type of Ethernet General Description
10BASE5 Commonly called “thick-net”; uses coaxial cabling
10BASE2 Commonly called “thin-net”; uses coaxial cabling
10BASE-T First type of Ethernet to use twisted-pair cabling
DIX Ethernet Version 2 Layer 1 and Layer 2 specifications for original Ethernet, from Digital/Intel/
Xerox; typically called DIX V2
IEEE 802.3 Called MAC due to the name of the IEEE committee (Media Access
Control); original Layer 1 and 2 specifications, standardized using DIX V2 as
a basis
IEEE 802.2 Called LLC due to the name of the IEEE committee (Logical Link Control);
Layer 2 specification for header common to multiple IEEE LAN
specifications
IEEE 802.3u IEEE standard for Fast Ethernet (100 Mbps) over copper and optical cabling;
typically called FastE
IEEE 802.3z Gigabit Ethernet over optical cabling; typically called GigE
IEEE 802.3ab Gigabit Ethernet over copper cabling
Foundation Summary 23
The internal processing algorithms used by switches vary among models and vendors; regardless,
the internal processing can be categorized as one of the methods listed in Table 1-9.
Table 1-10 lists some of the most popular Cisco IOS commands related to the topics in this chapter.
Table 1-9 Switch Internal Processing
Switching Method Description
Store-and-forward The switch fully receives all bits in the frame (store) before forwarding the
frame (forward). This allows the switch to check the FCS before forwarding
the frame, thus ensuring that errored frames are not forwarded.
Cut-through The switch performs the address table lookup as soon as the Destination
Address field in the header is received. The first bits in the frame can be sent
out the outbound port before the final bits in the incoming frame are received.
This does not allow the switch to discard frames that fail the FCS check, but
the forwarding action is faster, resulting in lower latency.
Fragment-free This performs like cut-through switching, but the switch waits for 64 bytes to
be received before forwarding the first bytes of the outgoing frame. According
to Ethernet specifications, collisions should be detected during the first 64
bytes of the frame, so frames that are in error because of a collision will not be
forwarded.
Table 1-10 Catalyst IOS Commands for Catalyst Switch Configuration
Command Description
interface vlan 1 Global command; moves user to interface configuration mode for a
VLAN interface
interface fastethernet 0/x Puts user in interface configuration mode for that interface
duplex {auto | full | half} Used in interface configuration mode; sets duplex mode for the
interface
speed {10 | 100 | 1000 | auto |
nonegotiate}
Used in interface configuration mode; sets speed for the interface
show mac address-table [agingtime
| count | dynamic | static]
[address hw-addr] [interface
interface-id] [vlan vlan-id]
Displays the MAC address table; the security option displays
information about the restricted or static settings
show interface fastethernet 0/x Displays interface status for a physical 10/100 interface
show interface vlan 1 Displays IP address configuration for VLAN
24 Chapter 1: Ethernet Basics
Table 1-11 outlines the types of UTP cabling.
Table 1-12 lists the pertinent details of the Ethernet standards and the related cabling.
Table 1-11 UTP Cabling Reference
UTP
Category
Max Speed
Rating Description
1 — Used for telephones, and not for data
2 4 Mbps Originally intended to support Token Ring over UTP
3 10 Mbps Can be used for telephones as well; popular option for Ethernet in
years past, if Cat 3 cabling for phones was already in place
4 16 Mbps Intended for the fast Token Ring speed option
5 1 Gbps Very popular for cabling to the desktop
5e 1 Gbps Added mainly for the support of copper cabling for Gigabit Ethernet
6 1 Gbps+ Intended as a replacement for Cat 5e, with capabilities to support
multigigabit speeds
Table 1-12 Ethernet Types and Cabling Standards
Standard Cabling
Maximum Single Cable
Length
10BASE5 Thick coaxial 500 m
10BASE2 Thin coaxial 185 m
10BASE-T UTP Cat 3, 4, 5, 5e, 6 100 m
100BASE-FX Two strands, multimode 400 m
100BASE-T UTP Cat 3, 4, 5, 5e, 6, 2 pair 100 m
100BASE-T4 UTP Cat 3, 4, 5, 5e, 6, 4 pair 100 m
100BASE-TX UTP Cat 3, 4, 5, 5e, 6, or STP, 2 pair 100 m
1000BASE-LX Long-wavelength laser, MM or SM fiber 10 km (SM)
3 km (MM)
1000BASE-SX Short-wavelength laser, MM fiber 220 m with 62.5-micron fiber;
550 m with 50-micron fiber
1000BASE-ZX Extended wavelength, SM fiber 100 km
1000BASE-CS STP, 2 pair 25 m
1000BASE-T UTP Cat 5, 5e, 6, 4 pair 100 m
Memory Builders 25
Memory Builders
The CCIE Routing and Switching written exam, like all Cisco CCIE written exams, covers a fairly
broad set of topics. This section provides some basic tools to help you exercise your memory about
some of the broader topics covered in this chapter.
Fill in Key Tables from Memory
Appendix E, “Key Tables for CCIE Study,” on the CD in the back of this book contains empty sets
of some of the key summary tables in each chapter. Print Appendix E, refer to this chapter’s tables
in it, and fill in the tables from memory. Refer to Appendix F, “Solutions for Key Tables for CCIE
Study,” on the CD to check your answers.
Definitions
Next, take a few moments to write down the definitions for the following terms:
Auto-negotiation, half duplex, full duplex, cross-over cable, straight-through cable,
unicast address, multicast address, broadcast address, loopback circuitry, I/G bit, U/L bit,
CSMA/CD
Refer to the glossary to check your answers.
Further Reading
For a good reference for more information on the actual FLPs used by auto-negotiation, refer to
the Fast Ethernet web page of the University of New Hampshire Research Computing Center’s
InterOperability Laboratory, at http://www.iol.unh.edu/services/testing/fe/training/.