Ccent Icnd1 100-105 (Last Updated 2/21/17)

Front 1

TCP/IP Model

Back 1

Application
Transport
Internet
Data Link/Physical

Front 2

TCP/IP Link Protocols

Back 2

Ethernet, PPP, T1

Front 3

TCP/IP Internet Protocols

Back 3

IP

Front 4

TCP/IP Transport Protocols

Back 4

TCP, UDP

Front 5

TCP/IP Application Protocols

Back 5

HTTP, POP3, SMTP

Front 6

TCP/IP Application Layer

Back 6

Provides services to the application software running on a computer, it does not define the application itself, but it defines services that applications need.

Front 7

Adjacent-layer interaction

Back 7

On a single computer, one layer provides a service to a higher layer, and it requires the lower layer to perform the needed function.

Front 8

Same-layer interaction

Back 8

Two computers use a protocol to communicate with the same layer on another computer.

Front 9

TCP/IP Encapsulation process

Back 9

1. Create and encapsulate the "application" data with any required application layer headers
2. Encapsulate the data supplied by the "application" layer inside a "transport" layer header. TCP and UDP headers is typically used.
3. Encapsulate the data supplied by the "transport" layer inside a "network" layer ip header. Ip defines the address that's unique to each computer
4. Encapsulate the data supplied by the "network" layer inside a "data link" layer header and trailer.
5. Transmit the bits. The physical layer encodes a signal onto the medium to transmit the frame.

Front 10

What do you call the header for TCP/IP Transport Layer

Back 10

Segment

Front 11

What's the header for TCP/IP Network Layer

Back 11

Packet

Front 12

Header for TCP/IP Link Layer

Back 12

Frame

Front 13

OSI application, presentation, session protocols

Back 13

Telnet, HTTP, FTP, SMTP, POP3, VoIP, SNMP

Front 14

OSI Transport protocols

Back 14

TCP, UDP

Front 15

OSI Network protocols

Back 15

IP

Front 16

OSI Data link protocols

Back 16

Ethernet, HDLC

Front 17

OSI Physical protocols

Back 17

RJ-45, Ethernet

Front 18

PDU

Back 18

Used by the OSI model, it represents the bits that include the headers and trailers for that layer, as well as the encapsulated data. "Protocol Data Unit"

Front 19

What is crosstalk

Back 19

EMI between wire pairs in the same cable

Front 20

IEEE

Back 20

Ether net standards, the all include the number 802.3

Front 21

10BASE-T

Back 21

Ethernet, 10Mbps

Front 22

100BASE-T

Back 22

Fast Ethernet, 100Mbps

Front 23

1000BASE-LX

Back 23

Gigabit Ethernet, 1000Mbps. Fiber

Front 24

1000BASE-T

Back 24

Gigabit Ethernet, 1000Mbps, Copper

Front 25

10GBASE-T

Back 25

10 Gig Ethernet, 10 Gbps

Front 26

Crossover Cable

Back 26

The endpoints transmit on different pin pairs. 1 and 3 are switched and 2 and 6. Same type of device (Switch to switch, router to router, switch to hub, router to PC)

Front 27

Straight-through cable

Back 27

The endpoints transmit on the same pin pair. Different type of device (switch to router, switch to PC, switch to server, switch to hub)

Front 28

OUI

Back 28

Organizationally unique identifier. Given to MAC address by the manufacturer, on the first 24 bits.

Front 29

Unicast address

Back 29

One to one device on the LAN

Front 30

Multicast address

Back 30

One to many devices on the LAN

Front 31

Broadcast address

Back 31

One to all devices on the LAN

Front 32

FCS

Back 32

Frame Check Sequence, a field in many DATA LINK TRAILERS used as part of the error-detection process. TCP.

Front 33

Steps of data being sent over Ethernet LAN

Back 33

1. PC 1 builds and sends the original Ethernet frame, using its own MAC address a the source address and PC2's MAC address as the destination address.
2. Switch SW1 receives and forwards the Ethernet frame out its G0/1 interface to SW2.
3. Switch SW2 receives and forwards the Ethernet frame out its F0/2 interface to PC2
4. PC2 receives the frame, recognizes the destination MAC address as its own, and processes the frame.

Front 34

Hubs are considered a device in which layer?

Back 34

Layer 1

Front 35

CSMA/CD

Back 35

Carrier sense multiple access with collision detection, half-duplex. Listens to see if Ethernet is not busy, then sends the frame, if collision occurs it sends a jamming signal to let the nodes know a collision happened, then they choose a random time to wait before trying to send the frame again.

Front 36

WANs and LANs are part of which OSI Layer(s)

Back 36

Layers 1 and 2

Front 37

DTE

Back 37

Data Terminal equipment, its a cable used between a router and an external CSU/DSU

Front 38

CSU/DSU

Back 38

Channel service unit/data service unit, an internal card that acts like a NIC sending and receiving data

Front 39

DCE

Back 39

Data Communication equipment, has a female connector, normally provides the function of clocking, the transmit and receive wires are swapped similar to what a crossover cable looks like.

Front 40

Two popular data-link layer protocols

Back 40

HDLC and PPP

Front 41

HDLC

Back 41

High-Level Data Link Control, does not have a "type" field. When sent by a router, it only goes to the other end of the link., data link layer protocol

Front 42

Steps of Routers De-encapsulating and Re-encapsulating IP Packets

Back 42

1. PC1 encapsulates the IP packet in an Ethernet frame that has the destination MAC address of R1.
2. R1 de-encapsulates the IP packet from the Ethernet frame, encapsulates the packet into an HDLC frame using an HDLC header and trailer, and forwards the HDLC frame to Router R2 next.
3. R2 de-encapsulates the IP packet from the HDLC frame, encapsulates the packet into an Ethernet frame that has the destination MAC address of PC3 and forwards the Ethernet frame to PC2.

Front 43

EoMPLS

Back 43

Ethernet over Multiprotocol Label Switching. It works as a PPP connection between two customer devices and it behaves as if a fiber Ethernet link existed between the two devices. This is a technology that can be used withing the SP'S cloud.

Front 44

WAN technologies

Back 44

DSL (uses analog lines) and Cable (uses cable TV cable)

Front 45

PSTN

Back 45

Public Switched Telephone Network, its a switch that supports the ability to set up voice calls, take them down, and forward them.

Front 46

DSLAM

Back 46

DSL access multiplexer. It splits the voice from the connection to the internet.

Front 47

Asymmetric speed

Back 47

Supported by DSL and Cable. Transmission from ISP downstream is faster than upstream.

Front 48

DSL

Back 48

Digital Subscriber Line, uses phone analog lines.

Front 49

Routing steps when sending packets

Back 49

If it doesn't see the ip address on its LAN, it sends the IP packet to its DEFAULT ROUTER, the router then looks at its ROUTING TABLE and checks looks at its GROUPINGS also called IP NETWORKS AND IP SUBNETS. It compares the DESTINATION IP to the entries on its ROUTING TABLE. Then that router sends it via EoMPLS to its next destination. When it reaches the other ROUTER, it then uses the DATA LINK LAYER and adds the appropriate HEADER and TRAILER to the packet before sending it via the PHYSICAL layer.

Front 50

ARP

Back 50

Address Resolution Protocol. It dynamically learns the data-link address or MAC of an IP host connected to a LAN. Its how a router determines which data-link address to use.

Front 51

IP Subnet/IP Network

Back 51

Groups of IP addresses together in the same network.

Front 52

DDN

Back 52

Dotted-Decimal notation. Ip addresses consisting of a 32-bit number. Binary format

Front 53

TCP/IP Internetwork key points

Back 53

1. All IP addresses in the same group must not be separated from each other by a router.
2. IP addresses separated from each other by a router must be in a different group.

Front 54

Class A range

Back 54

1-126, unicast, 126 networks

Front 55

Class B range

Back 55

128-191, unicast, 16,384 networks

Front 56

Class C range

Back 56

192-223, unicast, 2 million plus networks

Front 57

Class D range

Back 57

224-239, multicast

Front 58

Class E range

Back 58

240-255, reserved

Front 59

What is subnetting?

Back 59

A flexible way for anyone to take a single Class A, B, or C IP network and subdivide it into even smaller groups of consecutive IP addresses.

Front 60

Steps of IPv4 host routing

Back 60

1. If the destination IP address is in the same IP subnet as I am, send the packet directly to that destination host.
2. Otherwise, send the packet to my default gateway

Front 61

Summary of Router Forwarding Logic

Back 61

1. Use the data-link FCS field to ensure that the frame had no errors; if errors occurred discard the frame.
2. Assuming that the frame was not discarded at Step1, discard the old header and trailer, leaving the IP packet.
3. Compare the IP packets destination IP address to the routing table, and find the route that best matches the destination address.
4. Encapsulate the IP packet inside a new data-link header and trailer, appropriate for the outgoing interface, and forward the frame.

Front 62

DNS

Back 62

Domain Name System, is how a PC finds the IP address used by the listed hostname. It starts by sending a request for the IP address, the server replies back with the address and then the PC sends the IP packet to the destination address.

Front 63

OSI Layer 4 and functions

Back 63

Transport Layer, error recovery and flow control

Front 64

TCP Functions

Back 64

Error recovery, flow control using windowing, connection establishment and termination, and ordered data transfer and data segmentation. Requires three-way handshake

Front 65

UDP Functions

Back 65

Multiplexing, uses NFS to perform recovery with application layer code

Front 66

What is multiplexing?

Back 66

The process of how a computer thinks when receiving data. It relies on a process called socket which consists of an IP address, transport protocol and a port number

Front 67

SNMP

Back 67

Simple Network Management Protocol, application layer protocol used specifically for network device management

Front 68

TFTP

Back 68

Trivial File Transfer Protocol, is a basic file transfer to move files from a router or switch.

Front 69

SMTP

Back 69

Simple Mail Transfer Protocol

Front 70

FTP Data and Control Port and Protocol

Back 70

20, 21, TCP

Front 71

SSH Data and Control Port and Protocol

Back 71

22, TCP

Front 72

Telnet Data and Control Port and Protocol

Back 72

23, TCP

Front 73

SMTP Data and Control Port and Protocol

Back 73

25, TCP

Front 74

DNS Data and Control Port and Protocol

Back 74

53, UDP

Front 75

DHCP Server and Client Data and Control Port and Protocol

Back 75

67, 68 UDP

Front 76

TFTP Data and Control Port and Protocol

Back 76

69, UDP

Front 77

HTTP Data and Control Port and Protocol

Back 77

80, TCP

Front 78

POP3 Data and Control Port and Protocol

Back 78

110, TCP

Front 79

SNMP Data and Control Port and Protocol

Back 79

161, UDP

Front 80

URI

Back 80

Uniform Resource Identifier, the information you enter in the web address which contains the protocol, server name, and webpage. HTTPS://WWW.CISCO.COM/TRAINING

Front 81

CLI

Back 81

Command Line Interface, text line interface where you enter a command and it sends it to the switch which tells the device what to do and also replies back messages of what action was taken..

Front 82

Different ways to access the CLI

Back 82

console port, Telnet, and SSH (encrypted)

Front 83

Default terminal emulator software settings

Back 83

9600 bits/second
No hardware flow control
8-bit ASCII
No parity bits
1 stop bit

Front 84

User Executive Mode

Back 84

Also called "User mode" allows you to execute a command but a message displays on what the command did on the switch. Shows up in the CLI as hostname>

Front 85

Enable Mode

Back 85

Also called "Privilidged Mode." Shows up in CLI as hostname# ; you can also run the "reload" command in this mode

Front 86

How many commands does CISCO store in its CLI buffer by default

Back 86

10

Front 87

hostname(config)#

Back 87

Global configuration

Front 88

hostname(config-line)#

Back 88

Line configuration, EX. line console 0, line vty 0 15

Front 89

hostname(config-if)#

Back 89

Interface mode

Front 90

hostname(vlan)#

Back 90

Vlan configuration

Front 91

RAM or DRAM

Back 91

stores active running configuration

Front 92

Flash Memory

Back 92

Stores CISCO IOS and configuration files

Front 93

ROM

Back 93

Stores bootstrap program that loads when switch is turned on.

Front 94

NVRAM

Back 94

Stores the startup configuration

Front 95

Commands for erasing startup config

Back 95

write erase
erase startup-config
erase nvram

Front 96

Steps to forward a frame on a switch

Back 96

1. Check the destination MAC address
2. Check the source MAC address
3. Creates L2 loop-free environment with other switches by using STP
4. If the destination MAC is not known the switch floods the frame out of all ports except the one it came in on.

Front 97

STP

Back 97

Spanning Tree Protocol, allows a switch to dynamically work around loops in a network topology. The switches exchange BPDU's messages with other switches to detect looks and then remove the loops by blocking switch interfaces.

Front 98

Cisco Catalyst switch default setting out of the box

Back 98

1. Interfaces are enabled by default

2. All interfaces are assigned to VLAN 1

3. 10/100 and 10/100/1000 int use autonegotiation by default

4. The MAC learning, forwarding, flooding logic all works by default.

5. STP is enabled by default

Front 99

Show mac address-table

Back 99

CLI command that lists all known MAC addresses in the MAC table

Front 100

Show mac address-table dynamic

Back 100

shows all the dynamically learned MAC addresses

Front 101

show interfaces status

Back 101

CLI commands, shows the status of the interfaces.

Front 102

show interfaces f0/1 counters

Back 102

CLI command lists statistics about incoming and outgoing frames on the interfaces

Front 103

show mac address-table dynamic interface

Back 103

Front 104

show mac address-table aging-time

Back 104

Switches remove entries that have not been used for a defined number of seconds, 300 seconds is default in most switches

Front 105

clear mac address-table dynamic

Back 105

Empties the MAC table of all dynamic entries

Front 106

CLI steps to configure console password

Back 106

line console 0

login

password hope

Front 107

CLI steps to configure telnet password

Back 107

line vty 0 15

login

password love

Front 108

CLI steps to configure secret password

Back 108

enable secret password

Front 109

CLI steps to configure local username and password

Back 109

line console 0

login local

username wendell secret odom

line vty 0 15

login local

username chris secret brown

Front 110

AAA

Back 110

Authorization, Accounting, Authentication.

Front 111

AAA Server

Back 111

A server that holds security information and provides services related to user login, usually used for login into cisco switches

Front 112

CLI steps to configure SSH on a switch

Back 112

Front 113

Transport input all

Transport input telnet ssh

Transport input none

Transport input telnet

Transport input ssh

Back 113

Supports telnet and ssh

Supports telnet and ssh

Supports neither

Supports only telnet

Supports only ssh

Front 114

Show ip ssh

Back 114

Verifies that the SSH server is enabled and view the version and configuration data

Front 115

Show ssh

Back 115

Lists information about the clients currently connected via ssh

Front 116

CLI steps for configuring IPv4 address on cisco switch

Back 116

SW1#config t

SW1 (config)#interface vlan 1

SW1 (config-if)ip address 192.168.1.200 255.255.255.0

SW1 (config-if)no shudown

SW1 (config-if)exit

SW1 (config)ip default-gateway 192.168.1.1

Front 117

CLI steps for a switch to learn its IP address via DHCP

Back 117

SW1#config t

SW1 (config)#interface vlan 1

SW1 (config-if)#ip address dhcp

SW1 (config-if)#no shutdown

Front 118

show running-config

Back 118

list the currently used configuration

Front 119

show dhcp lease

Back 119

Lists any information the switch acquires as a DHCP client. This includes IP address, subnet mask, and default gateway information

Front 120

show crypto key mypubkey rsa

Back 120

Lists the public and shared key created for use with SSH usin the crypto key generate rsa global configuration command

Front 121

terminal history size x

Back 121

Changes the length of the history buffer for the current user only, only for the current login to the switch

Front 122

show history

Back 122

Lists the commands in the current history buffer

Front 123

logging synchronous

Back 123

Console or vty mode. Tells IOS to send log messages to the user at natural break points between commands rather than in the middle of a line of output

Front 124

[no] logging console

Back 124

Global commands that disables or enables the display of log messages to the console

Front 125

exec-timeout minutes [seconds]

Back 125

Console or vty mode. Sets the inactivity timeout, so that after the defined period of no action, IOS closes the current user login session.

Front 126

speed {10|100|1000|auto}

Back 126

interface mode. Manually sets the speed to the listed speed or, with the auto setting, automatically negotiates the speed.

Front 127

duplex {auto|full|half}

Back 127

Interface mode. Manually sets the duplex to half or full, or to autonegotiate the duplex setting

Front 128

description text

Back 128

Interface mode. Lists any information text that the engineer wants to track for the interface, such as the expected device on the other end of the cable

Front 129

no duplex

no speed

no description

Back 129

Reverts to the default settings for each interface subcommand of speed auto, duplex auto, and the absence of a description command.

Front 130

Whats a switch speed and duplex default setting from the box

Back 130

autonegotiation

Front 131

IEEE autonegotiation

Back 131

user the slowest supported speed (often 10Mbps) and if speed is 10 or 100 use half duplex, otherwise use full duplex

Front 132

Cisco autonegotiation

Back 132

sense the speed without autonegotiation, but if it fails, default to IEEE standards. If speed is 10 or 100 use half duplex, otherwise use full duplex

Front 133

Hubs and autonegotiation

Back 133

They use the IEEE rules for choosing default settings and it also uses CSMA/CD algorithing to avoid collisions

Front 134

Port security

Back 134

A Cisco switch feature in which the switch watches Ethernet frames that come in an interface (a port) tracks the source MAC addresses of all such frames, and takes a security action if the number of different such MAC addresses is exceeded.

Front 135

Configuring port security

Back 135

1. Make the switch interface either a static access or trunk interface using the switchport mode access or the switchport mode trunk interface subcommands, respectively

2. Enable port security using the switchport port-security interface subcommand.

3. (Optional) Override the default maximum number of allowed MAC addresses associated with the interface (1) by using the switchport port-security maximum number interface subcommand.

4. (Optional) Override the default action to take upon a security violation (shutdown) using the switchport port-security violation {protect|restrict|shutdown} interface subcommand.

5. (Optional) Predefine any allowed source MAC addresses for this interface using the switchport port-security mac-address mac-address command. Use the command multiple times to define more than one MAC address.

6. (Optional) Tell the switch to "sticky learn" dynamically learned MAC addresses with the switchport port-security mac-address sticky interface subcommand

Front 136

Switchport port-security violation protect

Back 136

Discards offending traffic.

Front 137

Switchport port-security violation restrict

Back 137

Discards offending traffic, sends log and SNMP messages, Increments the violation counter for each violating incoming frame.

Front 138

Switchport port-security violation shutdown

Back 138

Discards offending traffic, sends log and SNMP messages, Increments the violation counter for each violating incoming frame, and disables the interface by putting it in an err-disabled state, discarding all traffic.

Front 139

show mac address-table secure [interface type number]

Back 139

Lists MAC addresses defined or learned on ports configured with port security

Front 140

show port-security interface type number

Back 140

Lists an interface's port security configuration settings and security operational status

Front 141

show port-security

Back 141

Lists one line per interface that summarizes the port security settings for any interface on which it is enabled.

Front 142

CSMA/CD

Back 142

Carrier sense multiple access with collision detection. A media access mechanism in which devices ready to transmit data first check the channel for a carrier. If no carrier is sensed for a specific period of time, a device can transmit. If two devices transmit at once, a collision occurs and is detected by all colliding devices. This collision subsequently delays retransmissions from those devices for some random length of time.

Front 143

What kind of topology to hubs have

Back 143

Star topology

Front 144

What are transparent bridges or bridges

Back 144

They sit in between hubs and divide network into multiple collision domains

Front 145

Key things about collision domains

Back 145

1. LAN switches and bridges place each separate interface into a separate collision domain

2. Routers place each LAN interface into a separate collision domain

3. LAN hubs do not place each interface into a separate collision domain

4. A modern LAN, with all LAN switches and routers, with full duplex on each link would not have collisions at all. But you should look at each Ethernet link as a separate collision domain in case of troubleshooting

Front 146

Key points about broadcast domains

Back 146

1. VLANs are broadcast domains

2. Routers, because they do not forward LAN broadcasts, create separate broadcast domains off their separate Ethernet interfaces.

Front 147

Campus LAN

Back 147

LAN created to support devices in a building or in multiple building in somewhat close proximity to one another

Front 148

Two-tier campus design

Back 148

Provides a place to connect end-user devices, and connects all access switches to the distribution switches. Also known as "collapsed core"

Front 149

Access switches

Back 149

Connect directly to end users, providing user device access to the LAN

Front 150

Distribution switches

Back 150

Provide a path through which the access switches can forward traffic to each other

Front 151

Star topology

Back 151

Design where one device connects to several others

Front 152

Full mesh topology

Back 152

All the links connect to each other

Front 153

Partial mesh topology

Back 153

Some links connect to others and some do not

Front 154

Hybrid topology

Back 154

A design that combines topology design concepts into a larger more complex design

Front 155

Three-Tier design

Back 155

Access layer provides connection for end-user devices, distribution layer provides an aggregation point for access switches, providing connectivity to the rest of the devices on the LAN, forwarding frames between switches, but not connecting directly to end-user devices. Core layer aggregates distribution switches in very large campus LANs, providing very high forwarding rates for the larger volume traffic

Front 156

802.3i

Back 156

10BASE-T, Ethernet, 10 Mbps, UTP, 100m

Front 157

802.3u

Back 157

100BASE-T, Fast Ethernet, 100 Mbps, UTP, 100m

Front 158

802.3z

Back 158

1000BASE-X, Gigabit Ethernet, 1000 Mbps (1 Gbps), Fiber

Front 159

802.3ab

Back 159

1000BASE-T, Gigabit Ethernet, 1000 Mbps, UTP, 100m

Front 160

802.3ae

Back 160

10GBASE-X, 10 GigE, 10 Gbps, Fiber

Front 161

802.3an

Back 161

10GBASE-T, 10 GigE, 10 Gbps, UTP

Front 162

802.3ba

Back 162

40GBASE-X, 40 GigE, 40 Gbps, Fiber

Front 163

802.3ba

Back 163

100GBASE-X, 100 GigE, 100 Gbps, Fiber

Front 164

1000BASE-SX

Back 164

Multimode fiber, 550m

Front 165

1000BASE-LX

Back 165

Multimode fiber or singlemode fiber, 550m

Front 166

WLAN

Back 166

Wireless LAN controller, it controls and manages all AP functions

Front 167

LWAP

Back 167

Lightweight AP, forwards data between the wired and wireless LAN, and specifically forwarding data through the WLC using a protocol like CAPWAP

Front 168

Benefits of VLAN's

Back 168

1. Reduce CPU overhead on each device by reducing the number of devices that receive each broadcast frame

2. Reduce security risk by reducing the number of hosts that receive copies of frames that the switches flood

3. To improve security for hosts that send sensitive data by keeping those hosts on a separate VLAN

4.Create more flexible designs that group users by department, or by groups that work together

5. To solve problems more quickly, because the failure domain for many problems is the same set of devices as those in the same broadcast domain

6. To reduce the workload for the STP by limiting a VLAN to a single access switch.

Front 169

VLAN trunking

Back 169

A Cisco proprietary messaging protocol used between cisco switches to communicate configuration information about the existence of VLAs, including the VLAN ID and VLAN name

Front 170

VLAN tagging and VLAN ID

Back 170

The sending switch adds another header to the frame before sending it over the trunk. This extra trunking header includes a VLAN ID field so that the sending switch can associate the frame with a particular VLAN ID, and the receiving switch can then know in what VLAN each frame belongs.

Front 171

ISL

Back 171

Inter-Switch Link is a cisco-proprietary protocol that maintains VLAN information as traffic flows between switches and routers.

Front 172

802.1Q

Back 172

The IEEE standardized protocol for VLAN trunking. It also uses the native VLAN which is usually VLAN 1, whenever a frame is sent and receive that does not have the 802.1Q header, it is assumed that the frame is for the native VLAN. Both switches must have the same native VLAN.

Front 173

Key things about VLAN's

Back 173

1. In a LAN, the devices in the VLAN need to be in the same subnet unless some devices are supposed to be in a different VLAN, then in that case they need to be in a different subnet.

2. Layer 2 switches can't route between VLAN's but layer 3 switches can.

3. Routers can route between VLAN's either by being connected with one cable to each switch or by using the method "router-on-a-stick" which makes one connection to the router a trunk connection

Front 174

Configuring steps for setting up VLAN trunking on a cisco switch via the CLI

Back 174

Front 175

show vlan brief

Back 175

Shows vlan, status, and configured to what vlan, it also shows names of vlan's, does not include operational trunks

Front 176

Switchport mode access

Back 176

Interface mode. Always act as an access (nontrunk) port

Front 177

Switchport mode trunk

Back 177

Interface mode. Always act as a trunk port

Front 178

Switchport mode dynamic desirable

Back 178

Interface mode. Initiates negotiation messages and responds to negotiation messages to dynamically choose whether to start using trunking

Front 179

Switchport mode dynamic auto

Back 179

Interface mode. Passively waits to receive trunk negotiation messages, at which point the switch will respond and negotiate whether to use trunking

Front 180

Data VLAN

Back 180

Same idea and configuration as the access VLAN on an access port, but defined as the VLAN on that link for forwarding the traffic for the device connected to the phone on the desk.

Front 181

Voice VLAN

Back 181

The VLAN defined on the link for forwarding the phone's traffic. Traffic in this VLAN is typically tagged with an 802.1Q header.

Front 182

Key things about IP telephony ports on switches

Back 182

1. Configure these ports like a normal access port to begin: Configure it as a static access port and assign it an access VLAN

2. Add one more command to define the voice VLAN switchport voice vlan 1

3. Look for the mention of the voice VLAN ID, but no other new facts, in the output of the show interfaces type number switchport command

4. Look for both the voice and data (access) VLAN IDs in the output of the show interfaces type number trunk command.

5. Do not expect to see the port listed in the list of operational trunks as listed by the show interfaces trunk command.

Front 183

vtp mode {server|client|transparent|off}

Back 183

Gloval config command that defines the VTP mode

Front 184

switchport access vlan vlan-id

Back 184

Interface subcommand that statically configures the interface into that one VLAN

Front 185

switchport trunk encapsulation {dot1q|isl|negotiate}

Back 185

Interface subcommand that defines which type of trunking to use, assuming that trunking is configured or negotiated

Front 186

switchport nonegotiate

Back 186

Interface subcommand that disables the negotiation of VLAN trunking

Front 187

show vtp status

Back 187

Lists VTP configuration and status information.

Front 188

Troubleshooting steps

Back 188

1. Problem isolation and documentation

2. Resolve or escalate

3. Verify or monitor

Front 189

What to look for when troubleshooting

Back 189

1. Examine interface status and statistics (show interfaces and show interfaces description)

2. Analyze where switches will forward frames (checking the MAC address and destination)

3. Analyze port security

4. Analyze VLANs and VLAN trunking

Front 190

what does up|down|notconnect mean in a switch interface status

Back 190

Not expected on LAN switch physical interfaces

Front 191

what does a down|down|err-disabled mean in a switch interface status

Back 191

Por security has disabled the interface

Front 192

Runts

Back 192

Frames that did not meet the minimum frame size requirement, can be caused by collisions

Front 193

Giants

Back 193

Frames that exceed the maximum frame size requirement

Front 194

Input Errors

Back 194

A total of many counters, including runts, giants, no buffer, CRC, frame, overrun, and ignored counts.

Front 195

CRC

Back 195

Received frames that did not pass the FCS math; can be caused by collisions.

Front 196

Frame

Back 196

Received frames that have an illegal format, for example, ending with a partial byte; can be caused by collisions.

Front 197

Packets Output

Back 197

Total number of packets (frames) forwarded out the interface

Front 198

Output Errors

Back 198

Total number of packets (frames) that the switch port tried to transmit, but for which some problem occurred. f

Front 199

Collisions

Back 199

Counter of all collisions that occur when the interface is transmitting a frame

Front 200

Late Collisions

Back 200

The subset of all collisions that happen after the 64th byte of the frame has been transmitted

Front 201

Steps to analyze the forwarding path

Back 201

1. Process functions on the incoming interface, if its in up/up state then apply port security, if the port is an access port, determine the interface VLAN, if the port is trunk, determine the frame's tagged VLAN

2. Make a forwarding decision, look at the frames destination MAC in the MAC address table, but only for the entires in the VLAN identified in step 1. If the destination MAC is... found (unicast) forward the frame out the only interface listed in the matched address table entry. Not found (unicast), flood the frame out all other access ports except incoming port in the same VLAN. Broadcast, flood the frame, with the same rules as the previous step.

Front 202

Three basic features that port security uses to determine which frames to filter.

Back 202

1. Limit which specific MAC addresses can send and receive frames on a switch interface, discarding frames to/from other MAC addresses

2. Limit the number of MAC addresses using the interface, discarding frames to/from MAC addresses learned after the maximum limit is reached.

3. A combination of the previous two points.

Front 203

Steps to analyze port security operation on an interface

Back 203

1. Identify all interfaces on which port security is enabled (show running-config or show port-security.)

2. Determine whether a security violation is currently occurring based in part on the violation mode of the interface's port security configuration. shutdown/restrict/protect

3. Compare the port security configuration to the diagram and to the Last Source Address field in the ouput of the show port-security interface command.

Front 204

Router (config-if)# switchport port-security violation shutdown

Back 204

The interface will be in an err-disabled state, and the port security port status will be secure-down

Front 205

Router (config-if)# switchport port-security violation restrict

Back 205

The interface will be in a connected state, the port security port status will be secure-up, but the show port-security interface command will show an incrementing violations counter

Front 206

Router (config-if)# switchport port-security violation protect

Back 206

The interface will be in a connected state, and the show port-security interface command will not show an incrementing violations counter

Front 207

Steps to analyze VLANs and VLAN trunks

Back 207

1. Identify all access interfaces and their assigned access VLANs and reassign into the correct VLANs as needed.

2. Determine whether the VLANSs both exist (configured or learned with VTP) and are active on each switch.

3. Check the allowed VLAN lists, on the switches on both ends of the trunk, and ensure that the lists of allowed VLANs are the same

4. Check for incorrect configuration settings that result in one switch operating as a trunk, with the neighboring switch not operating as a trunk.

Front 208

True or False

Switches configured as VTP servers and clients do not list the VLAN commands in the running-config nor the startup-config file.

Back 208

True

Front 209

Key facts about subnets

Back 209

1. Addresses in the same subnet are not separated by a router

2. Addresses in a different subnet are separated by at least one router

Front 210

How to determine the number of subnets

Back 210

You should plan for one subnet for every VLAN, point-to-point serial link, and ethernet emulation WAN link (EoMPLS)

Front 211

Whats the formula to determine subnet size

Back 211

2 to the h power - 2 (one for subnet and one for subnet broadcast)

Front 212

Features that extended the life of IPv4

Back 212

1. IPv6, larger address, 128 bit

2. Assigning a subset of public IP network to each company, instead of an entire public IP network, to reduce waste

3. NAT, which allows the use of private IP network

Front 213

Class A private

Back 213

10.0.0.0

Front 214

Class B private

Back 214

172.16.0.0 through 172.31.0.0

Front 215

Class C private

Back 215

192.168.0.0 through 192.168.255.0

Front 216

An unsubnetted classful network is made up of how many parts

Back 216

2, network part and host part

Front 217

A subnetted classful network is made up of how many parts

Back 217

3, network, subnet, host

Front 218

What are the three parts of a subnet

Back 218

Subnet number, subnet broadcast, and IP address

Front 219

Subnet number

Back 219

Also called the subnet ID or subnet address, this number identifies the subnet. It is the numberically smallest number in the subnet. It can't be used as an IP address by a host.

Front 220

Subnet broadcast

Back 220

Also called the subnet broadcast address or directed broadcast address, this is the last (numerically highest) number in the subnet. It also can't be used as an IP address by a host.

Front 221

IP addresses

Back 221

All the numbers between the subnet ID and the subnet broadcast address can be used as a host IP address.

Front 222

VLSM

Back 222

Variable- length subnet masks, the capability to specify a different subnet mask for the same Class A, B, or C network number on different subnets.

Front 223

Binary mask

Back 223

An IPv4 subnet mask written as a 32-bit binary number

Front 224

DDN

Back 224

Dotted-decimal notation, The format used for IPv4, in which four decimal values are used, separated by periods (dots)

Front 225

Decimal mask

Back 225

An IPv4 subnet mask written in dotted decimal notations: Ex 255.255.255.0

Front 226

Prefix mask

Back 226

A term to describe an IPv4 subnet mask when represented as a slash (/) follwed by a decimal number.

Front 227

CIDR Masks

Back 227

Another term for a prefix mask, one that uses prefix or CIDR notation, in which the mask is represented by a slash (/) followed by a decimal number

Front 228

How to determine prefix, network, subnet, and hosts

Back 228

1. Convert the mask to prefix format.

2. Determine network based on the class

3. Calculate subnet = prefix - network

4. Calculate hosts = 32 - prefix

5. Calculate hosts/subnet = 2 to the power of h - 2

6. Calculate number of subnet = 2 to the power of subnets

Front 229

Steps to install a router

Back 229

1. Connect any LAN cables to the LAN port.

2. If using an external CSU/DSU, connect the router's serial interface to the CSU/DSU and the CSU/DSU to the line from the telco

3. If using internal CSU/DSU, connect the router's serial interface to the line from telco

4. Connect the router's console port to a PC (using a rollover cable), as needed, to configure the router.

5. Connect a power cable from a power outlet to the power port on the router

6. Power on the router

Front 230

Differences in router CLI compared to switch CLI

Back 230

1. Switches use VLAN interfaces, routers use an IP address configured on each working interface

2. Routers have an aux port meant for an external modem and phone line for remote users to log into the router

3. Router IOS by default disallow both Telnet and SSH because of default setting transport input none in vty configuration mode.

Front 231

Interface line status

Back 231

Refers to the Layer 1 status

Front 232

Protocol status

Back 232

Refers generally to the Layer 2 status

Front 233

CLI command

clock rate 60

Back 233

Interface command that sets the seed at which the router supplies a clocking signal, applicable only when the router has a DCE cable installed. The unit is bits/second.

Front 234

show ip interface brief

Back 234

Lists a single line of information about each interface, IP address, line and protocol status, and the method with which the address was configured (manual or DHCP)

Front 235

show protocols [type number]

Back 235

Lists information about the listed interface (or all interfaces if the interface is omitted), including the IP address, mask and line/protocol status.

Front 236

Show controllers [type number]

Back 236

Lists many lines of information per interface, or for one interface, for the hardware controller of the interface. On serial interfaces, this command identifies the cable as either a DCE or DTE cable

Front 237

Steps taken by a host when forwarding IP packets

Back 237

1. If destination is local send directly. Find destination hosts MAC address. Use the already-known ARP table entry, or use ARP messages to learn information. Encapsulate the IP packet in a data-link frame, with the destination data-link address of the destination host.

2. If the destination is not local, send to the default gateway: Find the defaults gateway MAC address. Use the already-known ARP table entry, or use ARP messages to learn the information. Encapsulate the IP packet in a data-link frame, with the destination data-link address of the default gateway.

Front 238

Steps taken by a router when forwarding IP packets

Back 238

1. For each received data-link frame, choose whether or not to process the frame. Process it if (A) The frame has no errors per FCS field (B) The frame's destination data-link address is the router's address (or an appropriate multicast or broadcast address)

2. If choosing to process the frame at Step 1, de-encapsulate the packet from inside the data-link frame by removing header and trailer

3. Compare the packet's destination IP address to the routing table and find the route that matches the destination address. This route identifies the outgoing interface of the router and possibly the next-hop router.

4. Encapsulate the packet into a data-link frame appropriate for the outgoing interface by attaching a HDLC header (next routers MAC) and trailer. When forwarding out LAN interfaces, use ARP as needed to find the next device's MAC address

5. Transmit the frame out the outgoing interface, as listed in the matched IP route.

Front 239

Three common sources from which routers build IP routes

Back 239

1. Connected routes: Added because of the configuration of the ip address interface subcommand on the local router

2. Static routes: Added because of the configuration of the ip route gloval command on the local router

3. Routing protocols: Added as a function by configuration on all routers, resulting in a process by which routers dynamically tell each other about the network so thatt they all learn routes.

Front 240

Rules regarding when a router creates a connected router

Back 240

1. The interface is in a working state.

2. The interface has an IP address assigned through the ip address interface subcommand

Front 241

Three options for connecting a router to each VLAN

Back 241

1. Use a router, with one router LAN interface and cable connected to the switch for each and every VLAN.

2. Use a router, with a VLAN trunk connecting to a LAN switch.

3. Use a Layer 3 switch

Front 242

Concept of VLAN subinterfaces on a router

Back 242

1. Use the interface type number.subint command in gloval configuration mode to create a unique subinterface for each VLAN that needs to be routed.

2. Use the encapsulation dot1q vlan_id command in subinterface configuration mode to enable 802.1Q and associate one specific VLAN with the subinterface.

3. Use the ip address address mask command in the subinterface configuration mode to configure IP settings (address and mask)

Front 243

Two alternative methods to configure the native VLAN in a ROAS configuration

Back 243

1. Configure the ip address command on the physical interface, but without an encapsulation command; the router considers this physical interface to be using the native VLAN

2. Configure the ip address command on a subinterface, and use the encapsulation...native subcommand.

Front 244

Layer 3 Switching concept and configuration

Back 244

1. On 2960 switches use the sdm prefer lanbase-routing in global config mode and reload the switch

2. Use the ip routing command in gloval configuration mode to enable IPv4 routing on the switch

3. Use the interface vlan vlan_id command in global configuration mode to create VLAN interfaces for each VLAN for which the layer 3 switch is routing packets

4. Use the ip address address mask command in interface config mode to config an IP address and mask on the VLAN interface, enabling IPv4 on that VLAN interface.

5. Use the no shutdown command in interface configuration mode to enable the VLAN interface

Front 245

Troubleshooting checklist for routes that do appear in the IP routing table

Back 245

1. Is there a subnetting math error in the subnet ID and mask?

2. Is the next-hop IP address correct, and referencing an IP address on a neighboring router?

3. Is the outgoing interface correct. and referencing an interface on the local route

Front 246

Troubleshooting checklist for static routes that do not appear in the IP routing table

Back 246

1.The outgoing interface listed in the Troubleshooting checklist for routes that do appear in the IP routing table ip route command is not up/up

2. The next-hop router IP address listed in the ip route command is not reachable

3. A better competing router exists, and that competing route has a better (lower) administrative distance.

Front 247

encapsulation dot1q vlan-id [native]

Back 247

A subinterface subcommand that tells the router to use 802.1Q trunking, for a particular VLAN, and with the native keyword, to not encapsulate in a trunking header

Front 248

encapsulation isl vlan-identifier

Back 248

A subinterface subcommand that tells the router to use ISL trunking for a particular VLAN

Front 249

sdm prefer lanbase-routing

Back 249

A command on Cisco switches that enables the switch to support IP routing if configured

Front 250

show ip router

Back 250

Lists the router's entire routing table

Front 251

show ip route [connected | static | rip]

Back 251

Lists a subset of the IP routing table

Front 252

show ip route ip address

Back 252

Lists detailed information about the route that a router matches for the listed IP address

Front 253

show vlans

Back 253

Lists VLAN configuration and statistics for VLAN trunks configured on router

Front 254

show arp, show ip arp

Back 254

Lists the router's IPv4 ARP table

Front 255

clear ip arp [ip-address]

Back 255

Remves all dynamically learned ARP table entires

Front 256

default gateway/router

Back 256

On an IP host, the IP address of some router to which the host sends packets when the packet's destination address is on a subnet other than the local subnet

Front 257

ARP table

Back 257

A list of IP addresses of neighbors on the same VLAN, along with their MAC addresses, as kept in memory by hosts and routers

Front 258

next-hop router

Back 258

In an IP route in a routing table, part of a routing table entry that refers to the next IP router that should receive packets that patch the route.

Front 259

outgoing interface

Back 259

In an IP route in a roruting table, part of a routing table entry that refers to the local interface out which the local router should forward packets that match the route.

Front 260

sub interface

Back 260

One of the virtual interfaces on a single physical interface.

Front 261

VLAN interface

Back 261

A configuration concept inside Cisco switches, used as an interface between IOS running on the switch and a VLAN supported inside the switch, so that the switch can assign an IP address and send IP packets into that VLAN.

Front 262

Connected route

Back 262

On a router, an IP route added to the routing table when the router interface is both up and has an IP address configured. The route is for the subnet that can be calculated based on the configured IP address and mask.

Front 263

static route

Back 263

An IP route on a router created by the user configuring the details of the route on the local router.

Front 264

default route

Back 264

On a router, the route that is considered to match all packets that are not otherwise matched by some more specific route.

Front 265

host route

Back 265

A route with a /32 mask, which by irtue of this mask represents a route to a single host IP address.

Front 266

floating static route

Back 266

A static IP route that uses a higher administrative distance that other routes, typically routes learned by a routing protocol. As a result, the router will not use the static route if the routing protocol route has been learned, but then use the static route if the routing protocol fails to learn the route.

Front 267

network route

Back 267

A route for a classful network.

Front 268

administrative distance

Back 268

A means for one router to choose between multiple routes to reach the same subnet when those routes were learned by different routing protocols. The lower the AD, the better the source of the routing information.

Front 269

Comparisons of IGP's

Back 269

1. Is it distance vector or link state

2. Choosing the best route based on the metric

3. The speed of convergence

4. Is the protocol public standard (RIP, OSPF) or vendor standard (EIGRP)

Front 270

distance vector

Back 270

The logic behind the behavior of some interior routing protocols, such as RIP. DV routing algorithms call for each router to send its entire routing table in each update, but only to its neighbors. DV algorithms can be prone to routing loops but are simpler than link-state routing algorithms.

Front 271

Split horizon

Back 271

A distance vector feature that tells a router to omit some routes from an update sent out an interface

Front 272

route poisoning

Back 272

The practice of advertising a failed route, but with a special metric value called infinity.

Front 273

Key features of RIPv1

Back 273

1. Hop-count metric

2. Sets 15 as the largest metric for a working route

3. Sends full routing updates

4. Uses split horizon

5. Uses route poisoning, with metric 16 to mean "infinite"

Front 274

Key features of RIPv2

Back 274

1. Hop-count metric

2. Sets 15 as the largest metric for a working route

3. Sends full routing updates

4. Uses split horizon

5. Uses route poisoning, with metric 16 to mean "infinite"

But it also does a few more things unlike RIPv1

1.Sends mask in routing update, thereby supporting VLSM

2. Supports manual route summarization

3. Sends update to 224.0.0.9 multicast address'

4. Supports authentication

Front 275

Whats does RIPv2 do on a interface once enabled?

Back 275

1. The router sends routing updates out the interface

2. The router listens for an processes incoming updates on that same interface

3. The router advertises about the subnet connected to the interface

Front 276

show ip route

Back 276

Front 277

Administrative distance for connected routes

Back 277

0

Front 278

Administrative distance for static routes

Back 278

1

Front 279

Administrative distance for EIGRP

Back 279

90

Front 280

Administrative distance for OSPF

Back 280

110

Front 281

Administrative distance for RIPv1 and v2

Back 281

120

Front 282

Administrative distance for DHCP default route

Back 282

254

Front 283

Administrative distance for unknown

Back 283

255

Front 284

Contiguous network

Back 284

A network topology in which the subnets of network X are not separated by subnets of any other classful network

Front 285

Discontiguous network

Back 285

A network topology in which the subnets of network X are separated by subnets of some other classful network

Front 286

RIP troubleshooting issues

Back 286

1. The RIP network command controls where RIP operates. If a missing network command fails to enable RIP on an interface: (A) RIP will not advertise about that connected subnet and (B) RIP will not send advertisements out that interface or process received advertisements in that interface

2. The passive-interface command should not be used for interfaces that connect to other routers.

3. The no auto-summary command has an impact only on routers that directly connect to more than one classful network. However, the command is needed only if a discontiguous classful network exists.

4. Some non-RIP features impact RIP operation, namely... (A) Interfaces must bbe working for RIPv2 to use the interfaces (B) Two routers on the same link must have IP addresses in the same subnet for RIPv2 to exchange routing information (C) Note that ACLs can filter RIP update messages and therefore break RIP

Front 287

EGP

Back 287

Exterior gateway protocol, A routing protocol that was designed to exchange routing information between different autonomous systems

Front 288

metric

Back 288

A unit of measure used by routing protocol algorithms to determine the best route for traffic to use to reach a particular destination

Front 289

routing update

Back 289

A generic reference to any routing protocols messages in which it sends routing information to a neighbor

Front 290

passive interface

Back 290

With a routing protocol, a router interface for which the routing protocol is enabled on the interface, but for which the routing protocol does not send routing protocol messages out that interface

Front 291

autosummarization

Back 291

A routing protocol feature in which in which the router that sits at the boundary between different classful networks will automatically advertise a route for one entire classful network into the other classful network, and vice versa

Front 292

hop count

Back 292

The metric used by the RIP routing protocol. Each router in an IP route is considered a hop, so for example, if two other routers sit between a router and some subnet, that router would have a hop count of two for that route.

Front 293

CLI command router rip

Back 293

Global command that moves the user into RIP configuration mode

Front 294

CLI command network network-number

Back 294

RIP subcommand that lists a classful network number, enabling RIP on all of that router's interfaces in that classful network

Front 295

CLI command passive-interface default

Back 295

RIP subcommand that changes the default setting on RIP-enable interfaces to be passive instead of not passive

Front 296

CLI command no passive-interface {interface-type interface-number}

Back 296

RIP subcommand that tells RIP to no longer advertise RIP updates on the listed interface

Front 297

CLI command [no] auto-summary

Back 297

RIP subcommand that toggles on (auto-summary) and off (no auto-summary) the autosummarization feature of RIP

Front 298

CLI command maximum-paths number

Back 298

RIP subcommand that sets the number of equal-metric routes for the same subnet that RIP will add to the IP routing table

Front 299

CLI command default-information originate

Back 299

RIP subcommand that causes RIP to adverise a default route- a route for prefix 0.0.0.0 mask 0.0.0.0 - if the local router has a default route in its routing table already

Front 300

CLI command ip address dhcp

Back 300

Interface subcommand that causes a router to act as a DHCP client, learning the IPv4 address to use on the interface and dynamically learning a default route that uses the DHCP-announce default gateway address as the next-hop IP address in a static route.

Front 301

Whats the process to lease an IP address between a client and a server

Back 301

DORA

Discover: Sent by the DHCP client to find a willing DHCP server

Offer: Sent by a DHCP server to offer to lease to that client a specific IP address

Request: Sent by the DHCP client to ask the server to lease the IPv4 address listed in the Offer message

Acknowledgment: Sent by the DHCP server to assign the address, and to list the mask, default router, and DNS server IP address

Front 302

IP addresses that allow a DHCP host with no IP address to still be able to send and receive messages on the local subnet

Back 302

0.0.0.0 An address reserved for use as a source IPv4 address for hosts that do not yet have an IP address

255.255.255.255 The local broadcast IP address. Packets sent to this destination address are broadcast on the local data link, but routers do not forward them.

Front 303

Four logic steps created by the ip helper-address command

Back 303

1. Watch for incoming DHCP messages, with destination IP address 255.255.255.255

2. Change that packet's source IP address to the router's incoming interface IP address from the host.

3. Change that packet's destination IP address to the address of the DHCP server (as configured in the ip helper-address command)

4. Route the packet to the DHCP server

Front 304

DHCP troubleshooting checklist

Back 304

1. If using a centralized DHCP server, at least one router on each remote subnet that has DHCP clients must act as DHCP relay agent, and have a correctly configured ip helper-address address subcommand on the interface connected to that subnet.

2. If using a centralized IOS DHCP server, make sure the DHCP pools network commands match the entire network's list of router interfaces that have an ip helper-address command pointing to this DHCP server.

3. Troubleshoot for any IP connectivity issues between the DHCP relay agent and the DHCP server, using the relay agent interface IP address and the server IP address as the source and destination of the packets.

4. Troubleshoot for any LAN issues between the DHCP client and the DHCP relay agent.

Front 305

Verification checklist for comparing host IPv4 settings with default router IPv4 settings

Back 305

1. The host link to the LAN and the default router link to the LAN must be in the same VLAN

2. The host and default router IP addresses must be in the same subnet

3. The host default router setting must refer to the same IP address configured on the router. (In other words, if the host claims the default router is 10.1.1.1, make sure the router interface IP address is not 10.1.1.2)

4. The LAN switches must not discard the frame because of the port security configuration.

Front 306

Different types of IPv4 broadcast addresses

Back 306

1. Local broadcast address: 255.255.255.255. Used to send a packet on a local subnet, knowing that routers will not forward the packet as in. Also called a limited broadcast.

2. Subnet broadcast address: One reserved address for each subnet. A packet sent to a subnet broadcast address can be routed to the router connected to that subnett, and then sent as a data link broadcast to all hosts in that one subnet. Also called an all-hosts broadcast or directed broadcast.

3. Network broadcast address: One reserved address for each classful network, namely the numerically highest number in the network. Used to send one packet to all hosts in that one network. Also called an all-subnets broadcast, referring to the fact that the packet reaches all subnets in a network.

Front 307

Unicast address are used for...

Back 307

web, email, chat, assigned to hosts with DHCP, and uses A/B/C classes

Front 308

Broadcast address are used for...

Back 308

Primarily used by protocols like DHCP and ARP to send to multiple devices, and used as destination IP address only

Front 309

Multicast address are used for...

Back 309

Used as destination IP address only, used by applications to send the same data at the same time to multiple clients, and is class D address.

Front 310

CLI command

ip dhcp exluded-address first last

Back 310

A gloval command that reserves an inclusive range of addresses, so that the DHCP server function does not lease out these addresses.

Front 311

CLI command

ip dhcp pool pool-name

Back 311

A global command that creates a pool, by name, and moves the user to DHCP server pool configuration.

Front 312

CLI command network subnet-id {ddn-mask |/prefix-length}

Back 312

A DHCP pool mode subcommand that defunes a network or subnet causing the DHCP server to lease out IP addresses in that subnet

Front 313

CLI command

default-router address1 address2...

Back 313

A DHCP pool mode subcommand that defines one or more routers as default routers, with that information passed for clients served by this pool

Front 314

CLI command

dns-server address1 address2

Back 314

A DHCP pool mode subcommand that defines the list of DNS servers that the DHCP server will list for clients served by this pool

Front 315

CLI command

lease {days[hours[minutes]] infinite}

Back 315

A DHCP pool mode subcommand that defines the length of time for a DHCP lease, for clients served by this pool

Front 316

CLI command

ip helper-address IP-address

Back 316

An interface subcommand that tells the router to notice local subnet broadcasts (to 255.255.255.255) that use UDP, and change the source and destination IP address, enabling DHCP server to sit on a remote subnet.

Front 317

CLI command

show arm, show ip arp

Back 317

Lists the router's IPv4 ARP table

Front 318

CLI command

show ip dhcp binding

Back 318

Lists the currently leased IP addresses on a DHCP server, along with the client identifier and lease time information

Front 319

CLI command

show ip dhcp pool name

Back 319

Lists the configured range of addresses in the pool, along with usage statistics and utilization high/low-water marks

Front 320

CLI command

show ip dhcp server statistics

Back 320

Lists statistics about the request by the DHCP server

Front 321

CLI command

show ip dhcp conflict

Back 321

Lists the IP addresses that the DHCP server found were already in use when the server tried to lease the address to a host

Front 322

CLI command

clear ip dhcp conflict

Back 322

Removes all entries from the DHCP servers conflict list

Front 323

Calculate the shortest prefix mask based on the minimum value of subnets

Back 323

P = N + S

Front 324

Calculate the shortest prefix mask based on the minimum value of hosts

Back 324

P = 32 - H

Front 325

The shorter three-step process to find all prefix masks that meet certain requirements

Back 325

The process to find the masks just requires a few steps, after you know N and the minimum values of S and H. The process finds the value of /P when using the least number of subnet bits, and when using the least number of host bits, as follows:

Step 1.Calculate the shortest prefix mask (/P) based on the minimum value of S, where P = N + S.

Step 2.Calculate the longest prefix mask (/P) based on the minimum value of H, where P = 32 – H.

Step 3.The range of valid masks includes all /P values between the two values calcu-lated in the previous steps.

Front 326

Reasons to choose one subnet mask versus another

Back 326

To maximize the number of hosts/subnet: To make this choice, use the shortest prefix mask (that is, the mask with the smallest /P value), because this mask has the largest host part.

To maximize the number of subnets: To make this choice, use the longest prefix mask (that is, the mask with the largest /P value), because this mask has the largest subnet part.

To increase both the numbers of supported subnets and hosts: To make this choice, choose a mask in the middle of the range, which gives you both more subnet bits and more host bits.

Front 327

Classless routing protocols

Back 327

RIPv2, EIGRP, OSPF. They all support VLSM

Front 328

Classfull routing protocols

Back 328

RIPv1

Front 329

Steps when adding a new subnet to existing VLSM design

Back 329

Step 1. Pick the subnet mask (prefix length) for the new subnet, based on the designrequirements (if not already listed as part of the question).

Step 2. Calculate all possible subnet numbers of the classful network using the maskfrom Step 1, along with the subnet broadcast addresses.

Step 3. Make a list of existing subnet IDs and matching subnet broadcast addresses.

Step 4. Compare the existing subnets to the candidate new subnets to rule out overlappingnew subnets.

Step 5. Choose the new subnet ID from the remaining subnets identified at Step 4,paying attention to whether the question asks for the numerically lowest ornumerically highest subnet ID.

Front 330

Classful routing protocol

Back 330

Does not transmit the mask information along with the subnet number, and therefore must consider Class A, B, and C network boundaries and perform autosummarization at the those boundaries. Does not support VLSM.

Front 331

Classless routing protocol

Back 331

An inherent characteristic of a routing protocol, specifically that the routing protocol does send subnet masks in its routing updates, thereby removing any need to make assumption about the addresses in a particular subnet or network, making it able to support VLSM and manual route summarization.

Front 332

Overlapping subnets

Back 332

An incorrect IP subnet design condition in which one subnet's range of addresses includes addresses in the range of another subnet.

Front 333

VLSM

Back 333

The capability to specify a different subnet mask for the same Class A, B, or C network number on different subnets. VLSM can help optimize available address space.

Front 334

Types of root causes of host connectivity problems that cannot be found by router ping commang

Back 334

■ ACLs that discard packets based on host A’s IP address, while that same ACL permitspackets matched on the router’s IP address

■ LAN switch port security issues that filter A’s packets (based on A’s MAC address)

■ IP routes on routers that happen to match host A’s 172.16.1.51 address, with differentroutes that match R1’s 172.16.1.1 address

■ Problems with host A’s default router setting

Front 335

Network layer problems that could cause a ping to fail between a route and host on the same LAN subnet

Back 335

■ IP addressing problem: Host A could be statically configured with the wrong IP address.■ DHCP problems: If you are using Dynamic Host Configuration Protocol (DHCP), manyproblems could exist: Host A could be using a different IP address than 172.16.1.51, theDHCP configuration could be wrong, the routers may be missing the DHCP relay configurationand so host A never got its IPv4 address lease, and so on.

■ VLAN trunking problems: The router could be configured for 802.1Q trunking, whenthe switch is not (or vice versa).

■ LAN problems: Any LAN problem discussed in Parts II and III of the ICND1 book, andPart I of the ICND2 book.

Front 336

Testing a host's default router setting using extended ping

Back 336

■ If a standard ping of a local LAN host works…

■ But an extended ping of the same LAN host fails…

■ The problem likely relates somehow to the host’s default router setting.

Front 337

Comparisons between ping and traceroute commands

Back 337

■ Both send messages in the network to test connectivity.

■ Both rely on other devices to send back a reply.

■ Both have wide support on many different operating systems.

■ Both can use a hostname or an IP address to identify the destination.

■ On routers, both have a standard and extended version, allowing better testing of thereverse route.

Front 338

Two places to look for routing problems when a traceroute command does not complete

Back 338

■ Connect to the CLI of the last router listed, to look at forward route issues.

■ Connect to the CLI of the next router that should have been listed, to look for reverseroute issues .

Front 339

Checklist of how to troubleshoot issues between the IPv4 settings on a host and its default router

Back 339

Step 1. Check the host’s list of DNS server addresses against the actual addresses usedby those servers.

Step 2. Check the host’s default router settings against the router’s LAN interface configuration,for the ip address command.Step 3. Check the subnet mask used by the router and the host; if they use a differentmask, the subnets will not exactly match, which will cause problems for somehost addresses.Step 4. The host and router should attach to the exact same subnet—same subnet IDand same range of IP addresses. So, use both the router’s and host’s IP addressand mask, calculate the subnet ID and range of addresses, and confirm they arein the same subnet as the subnet implied by the address/mask of the router’s ipaddress command

Front 340

Two root causes of DNS problems

Back 340

■ A user host (DNS client) that has an incorrect setting for the DNS server IP address(es)

■ An IP connectivity problem between the user’s host and the correct DNS server

Front 341

Conditions that must be true for DHCP messages to be able to flow from a client to a DHCP server

Back 341

Step 1. If using a centralized DHCP server, at least one router on each remote subnetthat has DHCP clients must act as DHCP relay agent, and have a correctly configuredip helper-address address subcommand on the interface connected tothat subnet.

Step 2. Troubleshoot for any IP connectivity issues between the DHCP relay agent andthe DHCP server, using the relay agent interface IP address and the server IPaddress as the source and destination of the packets.

Step 3. Whether using a local DHCP server or centralized server, troubleshoot for anyLAN issues between the DHCP client and the DHCP relay agent.

Step 4. Troubleshoot incorrect server configuration.

Front 342

Common reasons why router LAN interfaces are not up/up

Back 342

Front 343

show ip route field reference and explanations

Back 343

Front 344

Types of overlapping IP address configuration issues that IOS can and can't recognize

Back 344

Preventing the overlap on a single router: IOS detects the overlap when the ip addresscommand implies an overlap with another ip address command on the same router.Allowing the overlap on different routers: IOS cannot detect an overlap when an ipaddress command overlaps with an ip address command on another router.

Front 345

Summary of four main categories of IPv4 ACLs in Cisco IOS

Back 345

Front 346

Summary of first-match logic used by all ACLs

Back 346

ACLs use first-match logic. Once a packet matches one line in the ACL, the router takesthe action listed in that line of the ACL, and stops looking further in the ACL.

Front 347

Wildcard mask logic for decimal 0 and 255

Back 347

Decimal 0: The router must compare this octet as normal.

Decimal 255: The router ignores this octet, considering it to already match.

Front 348

Wildcard mask logic to match a subnet

Back 348

■ Use the subnet number as the source value in the access-list command.

■ Use a wildcard mask found by subtracting the subnet mask from 255.255.255.255