CCNA Review
This document is intended to help students understand what types of information would be required to pass the CCNA test. This is
only intended as a review and additional training and knowledge would be needed in order to take and pass the CCNA exam. This document
does not help with the simulation portion of the test.
Course Review Series
CCNA Review
1-800-COURSES www.globalknowledge.com
CCNA Review
Rick Chapin, Global Knowledge Instructor
Note: This document is intended to help students understand what types of information would be required to pass the CCNA test. This is
only intended as a review and additional training and knowledge would be needed in order to take and pass the CCNA exam. This document
does not help with the simulation portion of the test.
OSI Reference Points
OSI Layer Upper or Data Flow Layer Network Reference Network Device
Application Upper
Presentation Upper
Session Upper PDU or Message
Transport Data Flow Segment
Network Data Flow Packet or Datagram MultiLayer Switch or Router
Data Link Data Flow Frame Switch or Bridge
Physical Data Flow Bits and Signaling Hub
OSI Layers
OSI Layer Purpose Examples
Application Provides services to network applications. This layer is • Simple Mail Transport Protocol (SMTP)
responsible for determining resource availability, identi- • Telnet
fying communications peers, and synchronizing commu-
nications between the applications. • File Transfer Protocol (FTP)
• Trivial File Transfer Protocol (TFTP)
• HyperText transfer Protocol (HTTP)
Presentation Provides the coding and conversion functions that are • ASCII (text)
applied to the data to/from the Application layer. This • EBCDIC (text)
layer ensures that there is a common scheme used to
bundle the data between the two ends. There are vari- • JPEG (image)
ous examples and this list is by no means complete. • GIF (image)
Text can be either ASCII or EBCDIC. Images can be • TIFF (image)
JPEG, GIF, or TIFF. Sound can be MPEG or Quicktime
• MPEG (sound/video)
• Quicktime (sound/video)
Session Maintains communications sessions between upper- • Session Control Protocol (SPC)
layer applications. This layer is responsible for establish- • Remote Procedure Call (RPC) from Unix
ing, maintaining, and terminating such sessions
• Zone Information Protocol (ZIP) from AppleTalk
Copyright ©2005 Global Knowledge Network, Inc. All rights reserved. Page 2
Transport Responsible for end-to-end data transmission. These • Transmission Control Protocol (TCP) from IP
communications can be either reliable (connection-ori- • User Datagram Protocol (UDP) from IP
ented) or non-reliable (connectionless). This layer organ-
izes data from various upper layer applications into data
streams. The transport layer also handles end-to-end
flow control, multiplexing, virtual circuit management,
and error checking and recovery.
Network Uses administrator-defined logical addressing to com- • Internet Protocol (IP)
bine many data flows into an internetwork. This layer
allows both connection-oriented and connectionless data
flows to access the network. The network layer address-
es help define a network hierarchy. Network devices are
normally grouped together based on their common
Network Layer address.
Data Link Provides either reliable or non-reliable transmission of LAN:
data across a physical medium. Most networks use a • Ethernet/IEEE 802.3 (include Fast Ethernet)
non-reliable data link layer, such as Ethernet or Token
Ring. The data Link Layer provides a physical address to • 802.3z (Gigabit Ethernet)
each device called a Media Access Control (MAC) • Token Ring /IEEE 802.5
address. MAC addresses are typically burned into the • FDDI (from ANSI)
network interface card (NIC). The Data Link Layer also
WAN:
uses a Logical Link Control (LLC) to determine the type
of Network Layer data is traveling inside the frame. • High-Level Data-link Control (HDLC)
• Point-to-Point Protocol (PPP)
• Frame Relay
Physical Defines the electrical, mechanical, and functional specifi- LAN:
cations for maintaining a physical link between network • Category 3 cabling (LAN)
devices. This layer is responsible for such characteristics
as voltage levels, timing and clock rates, maximum trans- • Category 5 cabling (LAN)
mission distances, and the physical connectors used. WAN:
• EIA/TIA-232
• EIA/TIA-449
• V.35
Network Hierarchy
Layer Purpose Network Device
Core To move network traffic as fast as possible. • High-speed routers
Characteristics include fast transport to enterprise serv- • Multi-layer switches
ices and no packet manipulation.
Distribution Perform packet manipulation such as filtering (security), • Routers
routing (path determination), and WAN access (frame
conversion). The distribution layer collects the various
access layers. Security is implemented here, as well as
broadcast and multicast control. Media translation
between LAN and WAN frame types also occurs here.
Access Where end-stations are introduced to the network. This • Switches
is the entry point for virtually all workstations. • Bridges
• Hubs
Copyright ©2005 Global Knowledge Network, Inc. All rights reserved. Page 3
LAN Switch Functions
Function Purpose
Address Learning Dynamically learns MAC addresses that arrive in the switch by reading the sources MAC address of each
arriving frame. If this address is not in the current MAC table, and there is enough space to store it, the
address and the inbound port are stored.
Forward/Filter Compare the destination MAC address of the arriving frame to the dynamically-learned MAC table. If the
address is in the table only forward the frame out the port specified in the table, thus filtering it from other
ports. If the MAC address is not in the MAC table (unknown MAC address) or it is a broadcast or multicast
frame, the frame is flooded out every other port except the one it arrived from.
Loop Avoidance Since the default behavior of a switch is to forward unknown unicast, broadcast, and multicast frames, it is
possible for one frame to Loop endlessly through a redundant (multiple path) network. Thus the Spanning
Tree Protocol (STP) is turned on to discourage loops in a redundant switch network.
Sources of Switching/Bridging Loops
Source Description
Redundant Topology Unknown Frames are flooded out all ports. If there are multiple paths, than a flood would go out all ports,
except the originator, and come back in on the other ports, thus creating a loop.
Multiple Frame Copies Two machines live (connect) on the same wire. They send frames to each other without assistance. If there
are two bridges/switches attached to the same wire, who are also connected together, then new frames
(unknown) going from one machine (same wire) would go directly to the other machine (same wire) and
would also be flooded through the bridges/switches (connected wire) and be flooded back through the
bridges/switches to the original wire. The receiving machine would receive multiple copies of the same frame.
MAC Database Instability Thanks to a bridging/switching loop (senairo above), one bridge/switch learns the same MAC address on dif-
ferent ports. Thus, if a bridge/switch needed to forward a frame to its destination MAC address, it would have
two possible destination ports.
Solution to Bridging/Switching Loops – 802.1d Spanning Tree Protocol
• Bridges/switches communicate with Bridge Protocol Data Units (BPDUs). The BPDU carries the Bridge ID and the Root ID
• Each bridge/switch has a unique Bridge ID, which is the priority (or priority and extend system ID) followed by the base MAC address of
the bridge/switch. Only the priority (or priority and extend system ID) can be modified.
• The device with the lowest Bridge ID becomes the Root
• Only the Root is allowed to send BPDUs
• Initially, prior to receiving any BPDUs from other devices, every bridge/switch thinks it is the Root, and thus sends a BPDU to every other
Bridge/switch. This always occurs when a new Bridge/switch is added to an existing network.
• After the round of BPDUs, every bridge/switch becomes aware of the lowest Bridge ID (the Root device). Only the Root continues to send
BPDUs.
• BPDUs are sent, by default, every two (2) seconds.
• Every Bridge/switch receives BPDUs from the Root. If multiple BPDUs are received, then there must be a loop in the network. The BPDU
with the lowest cost is the best path to the Root.
• The goal of every non-root bridge/switch is to find the most efficient path to the Root.
• Ports that are not the most efficient path to the root, and are not needed to reach any other downstream bridge/switch, are blocked.
Blocked ports still receive BPDUs.
• If the primary path ceases to receive a BPDU, STP eventually forwards packets on an alternate port. Blocked ports are re-evaluated to find
the most efficient and that port is un-blocked so a path can be reestablished to the root.
Copyright ©2005 Global Knowledge Network, Inc. All rights reserved. Page 4
• Forwarding ports are also called Designated ports (DP).
• Blocked ports are also called non-Designated ports (BLK).
• The port that is forwarding to the Root is called the Root port (RP).
• The Root Bridge/switch ports never block and are always designated ports (DP).
• Bridge/switch convergence is the time between a break occurring and an STP calculating an alternate path. Typically 30 – 50 seconds.
• Port convergence is the time it takes for STP to calculate whether a port will be in forwarding or blocking mode. Typically 50 seconds.
Comparison of Bridges and Switches
Bridges Switches
Software Based Hardware-based (port-level ASICs)
Relatively Slow Comparatively fast
One STP per Bridge Possibly many STPs per switch (possibly one per VLAN)
Typically up to 16 Ports Possibly hundreds of ports
Forwarding Modes in a Switch
Mode Description Latency
Store-and-Forward The entire frame is buffered, the CRC is examined for Relatively High. Varies depending on frame size.
errors and frame is checked for correct sizing (Ethernet
64 – 1518 bytes).
Cut-Through The frame is forwarded once the destination MAC Lowest. Fixed delay based on 6 bytes being buffered.
address (first 6 bytes) arrives and is checked against the Not configurable on a Catalyst 1900.
MAC address table. Buffer until the 6th byte arrives.
Fragment-Free (Cisco) The frame is forwarded once the first 64 bytes have Low. Fixed delay based on 64 bytes being buffered.
arrived. Buffering occurs until the 64th byte arrives. Default on Catalyst 1900.
Ethernet collisions usually occur within the first 64
bytes, thus if 64 bytes arrive there is no collision.
Half-Duplex vs. Full-Duplex
Duplex Type Advantages Defaults
Half-Duplex • Network devices us the same pair of wire to both transmit and receive 10 Mbps. 100 Mbps ports if not config-
• Only possible to use 50% of the available bandwidth – must use the same ured for full-duplex or cannot be Auto-
bandwidth to send and receive sensed.
• Available bandwidth decreases as number of devices in the broadcast domain
increases
• Used through hubs (layer 1 devices) – everyone shares the available bandwidth
Full-Duplex • Uses one pair of wire for sending and another pair for receiving. 100 Mbps ports if manually configured
• Effectively provides double the bandwidth – possible to send and receive at for full-duplex or can be Auto-sensed
the same time.
• Must be point-to-point stations, such as pc/server-to-switch or router-to-switch.
• Everyone has their own collision domain (individual bandwidth) on each
switch port.
Copyright ©2005 Global Knowledge Network, Inc. All rights reserved. Page 5
LAN Segmentation = Dividing Up the Size of Collision Domains
Device Abilities
Bridge Examines destination MAC address and makes filtering/forwarding decisions based on it. Unknown, Broadcast, and
Multicast frames are flooded out all ports except the originator. Each port of a bridge is a collision domain.
Switch (VLANs) Examines destination MAC address and makes filtering/forwarding decisions based on it. Unknown, Broadcast, and
Multicast frames are flooded out all ports within that VLAN except the originator. Each port of a switch is a collision
domain. Each VLAN is a broadcast domain. Benefits include simplifying moves, adds, and changes, reducing adminis-
trative costs, controlling broadcasts, tightened security, load distribution, and moving servers into a secure location.
Router Examines destination network (logical – layer3) address and makes filtering/forwarding decisions based on it.
Unknown and broadcast frames are discarded. Each port of a router is both a collision and broadcast domain.
TCP/IP Layers
Protocol OSI Reference Function
Transmission Control Session Layer – Layer 4 Reliable, connection-oriented, uses sequence and acknowledgement numbers
Protocol (TCP) to provide reliability verifies that the remote end is listening prior to sending
data (handshake).
User Datagram Protocol Session Layer – Layer 4 Non-reliable, connectionless, no sequence or acknowledgement numbers, and
(UDP) no far-end verification.
Internet Protocol (IP) Network Layer – Layer 3 Provides the logical addressing structure. Offers connectionless, best-effort
delivery of packets (datagrams).
Port Numbers
Well-known port numbers are 1 – 1023 (typically used for well-known applications), random port numbers are 1024 and above (typically
random numbers are used by the client in a client/server application).
Application Port Transport
File Transfer Protocol (FTP) 20/21 TCP
Telnet 23 TCP
Simple Mail Transfer Protocol (SMTP) 25 TCP
Domain Name Services (DNS) 53 TCP
Domain Name Services (DNS) 53 UDP
Trivial Files Transfer Protocol (TFTP) 69 UDP
Simple Network Management Protocol (SNMP) 161/162 UDP
Routing Information Protocol (RIP) 520 UDP
Copyright ©2005 Global Knowledge Network, Inc. All rights reserved. Page 6
IP Protocols
Protocol Purpose
Internet Control Message Provides control and feedback messages between IP devices.
Protocol (ICMP)
Address Resolution Protocol Using a destination IP address, ARP resolves or discovers the appropriate destination MAC (layer 2) address
(ARP) to use. Map a Layer 3 address to a Layer 2 address.
Reverse Address Resolution Using a source MAC address, RARP retrieves an IP address form the RARP Server. Map sources Layer 2
Protocol (RARP) address to a Layer 3 address. RARP is an early form of BOOTP and DHCP.
IP Addresses
Number of Number of Hosts Number of Number of Hosts
Class First Binary Bits Numerical Range
Networks per Network Network Octets Octets
A 0xxx 1 – 126* 126 16.5 million 1 (N.H.H.H) 3
B 10xx 128 – 191 16 thousand 65 thousand 2 (N.N.H.H) 2
C 110x 192 – 223 2 million 254 3 (N.N.N.H) 1
D** 111x 224 – 239 N/A N/A N/A N/A
E** 1111 240 – 255 N/A N/A N/A N/A
* 127 is used for the Loopback address.
** Class D is used for Multicast Group addressing, and Class E is reserved for research use only.
Subnetting
Number of networks: 2s – 2, where s = number of bits in the subnet (masked) field
Number of hosts per subnet: 2r – 2, where r = number of host (non-masked) bits.
R + S = 32 (always), since there are 32 bits in an IP address and each bit is either a network or host bit. S is the bit(s) after the standard
Class number of bits (Mask – Class Bits = S).
Subnet Masks
1s in the subnet mask match the corresponding value of the IP address to be Network bits
0s in the subnet mask match the corresponding value in the IP address to be Host bits
Default Subnet Masks
Default Class A mask – 255.0.0.0 = N.H.H.H
Default Class B mask – 255.255.0.0 = N.N.H.H
Default Class C mask – 255.255.255.0 = N.N.N.H
Copyright ©2005 Global Knowledge Network, Inc. All rights reserved. Page 7
Possible Subnet Mask Values for One Octet
Decimal Mask Binary Mask Network Bits Host Bits
0 00000000 0 8
128 10000000 1 7
192 11000000 2 6
224 11100000 3 5
240 11110000 4 4
248 11111000 5 3
252 11111100 6 2
254 11111110 7 1
255 11111111 8 0
Possible Class C Subnet Masks
Number of Subnets Number of Hosts
Decimal Mask Network Bits (x) Host Bits (y)
2s – 2 2r – 2
255.255.255.0 0 8 0 254
255.255.255.128 1 7 N/A N/A
255.255.255.192 2 6 2 62
255.255.255.224 3 5 6 30
255.255.255.240 4 4 14 14
255.255.255.248 5 3 30 6
255.255.255.252 6 2 62 2
255.255.255.254 7 1 N/A N/A
255.255.255.255 8 0 N/A N/A
Routing
The process of maintaining a table of destination network addresses. A router will discard packets for unknown networks.
Sources of Routing Information
Source Description
Static • Manually configured by an administrator
• Must account for every destination network
• Each static route must be configured on each router
• No overhead in processing, sending, or receiving updates
• Saves bandwidth and router CPU
• Routing table maintained by administrator
Dynamic • A process that automatically exchanges information about available routes
• Uses metrics to determine the best path to a destination network
• The routing protocol must be configured on each router
• Bandwidth is consumed as routing updates are transmitted between routers
• Router CPU is used to process, send, and receive routing information
• Routing table maintained by routing process
Copyright ©2005 Global Knowledge Network, Inc. All rights reserved. Page 8
Types of Routing Protocol
Type Description
Interior • Used within a common administrative domain called an Autonomous System (AS)
• Typically a single AS is controlled by a single authority or company
• Interior routing protocols are used within a corporate network
Exterior • Used to connect Autonomous Systems
• Exchanges routing information between different administrative domains
• Exterior protocols are used to connect sites within a very large corporate network, or are used to connect to the Internet
Classes of Routing Protocol
Class Description
Distance Vector • Maintains a vector (direction and distance) to each network in the routing table
• Typically sends periodic (update interval) routing updates
• Typically sends entire routing table during update cycle
• Routing updates are processed and then resent by each router, thus the updates are second-hand information (routing
by rumor)
• Typically prone to routing loops (disagreement between routers) and count to infinity (routing metrics continue to
accumulate indefinitely)
• Solutions to these problems include:
- Spilt Horizon – do not send updates back to where they came from – eliminates back-to-back router loops
- Define a maximum metric – eliminates count to infinity problem
- Route poisoning – set the advertised metric to the maximum value on routes that have gone down
- Poison reverse – overrides split horizon by informing the source of a route that it has gone down
- Hold-down timers – eliminates long-distance loops by ignoring updates about “possibly down” routes that have
metrics worse than the current metric
- Triggered updates – send an individual update immediately when a route is thought to be down, rather than wait
for the periodic update timer (also called flash updates)
Link State • Maintains a complete topological map (database) of entire network, separate from the routing table (forwarding table)
• Sends updates only when necessary
• Only sends information that has changed, not the entire database
• Does not send information from the routing table, but rather from the database
• The initial routing update is sent to every link state router in the network (flooding) via a multicast IP address, not a
processed copy as with distance vector protocols
• Routing table is individually calculated on each router from its database. This process is called Shortest Path First or
SPF
• The database typically requires as much memory as the routing table
• When SPF runs, it is CPU intensive
• Uses “hello” packets to maintain a database of link state neighbors throughout the network
Copyright ©2005 Global Knowledge Network, Inc. All rights reserved. Page 9
Examples of Routing Protocols
DV or Internal or
Protocol Characteristics
LS External
Routing Information DV Internal • Sends periodic updates every 30 seconds by default
Protocol (RIP) • Sends the entire routing table out every interface, minus the routes learned from that
interface (split horizon)
• Uses hop count as a metric
• Has a maximum reachable hop count of 15 (16 is the defined maximum)
• Sends updates out as a broadcast (RIP V1)
• RIP V2 uses a multicast address of 244.0.0.10
Interior Gateway DV Internal • Sends periodic updates every 90 seconds by default
Routing Protocol • Sends the entire routing table out every interface, minus the routes learned from that
(IGRP) interface (split horizon)
• Uses a composite metric consisting of bandwidth, delay, reliability, load, and MTU
• Only uses bandwidth and delay by default (configurable)
• Does track hop count but only uses it as a tie-breaker
• Default maximum hop count is 100, but is configurable up to 255 maximum
• Sends updates out as a broadcast
Enhanced Interior Adv. DV Internal • Considered an advanced distance vector routing protocol
Gateway Routing • Uses a Diffusing update algorithm (DUAL)
Protocol (EIGRP)
• Sends triggered updates when necessary
• Sends only information that has changed, not entire routing table
• Uses a composite metric consisting of bandwidth, delay, reliability, load, and MTU
• Only uses bandwidth and delay by default (configurable)
• Does track hop count but only uses it as a tie-breaker
• Default maximum hop count is 224, but is configurable up to 255 maximum
• Sends updates out on a multicast address of 224.0.0.9
Open Shortest Path LS Internal • Sends triggered updates when necessary
First (OSPF) • Sends only information that has changed, not entire routing table
• Uses a cost metric
• Interface bandwidth is used to calculate cost (Cisco)
• Uses two multicast addresses of 224.0.0.5 and 224.0.0.6
Border Gateway DV External • Actually a very advanced distance vector routing protocol
Protocol (BGP) • Sends triggered updates when necessary
• Sends only information that has changed, not entire routing table
• Uses a complex metric system
Copyright ©2005 Global Knowledge Network, Inc. All rights reserved. Page 10
Routing Configuration Commands
Type Syntax
Static Router(config)# ip route dest-address subnet-mask next-hop or exit-interface
• dest-network is the network in question
• subnet-mask is the network in question
• next-hop is the network in question
• exit-interface is the network in question
- either the next-hop or exit-interface are used, but not both
Example:
Router# configure terminal
Router(config)# ip route 172.16.0.0 255.255.0.0 serial0
or
Router(config)# ip route 172.16.0.0 255.255.0.0 172.16.1.1
Dynamic Router(config)# router protocol keyword
Router(config-router) network network-number
• protocol is the routing protocol being used
• keyword is an optional parameter for some routing protocols
• network-number is the directly connected network that will be used to send and receive routing updates; enables all
interfaces that use that network address
Example 1:
Router# configure terminal
Router(config)# router rip
Router(config-router)# network 172.16.0.0
Router(config-router)# network 192.168.20.0
Example 2:
Router(config)# router IGRP 100
Router(config-router)# network 172.16.0.0
Router(config-router)# network 192.168.20.0
Router Storage Locations
Memory Type Contents
RAM Operating environment
MVRAM Backup (startup) copy of the configuration file, single file only
ROM IOS subset (RxBoot) (only if the hardware supports it
ROM Monitor (ROMMON)
Flash Compressed IOS (non-compressed if 2500 series)
Binary file storage capabilities (if enough space)
PCMCIA Like Flash, some machines have multiple PCMCIA slots available
Share I/O I/O buffer for interfaces
Copyright ©2005 Global Knowledge Network, Inc. All rights reserved. Page 11
Operating Modes of a Router
Mode Prompt Sample Functions
User Router> • Read-only privileges
• Examine Interface status
• Examine router status
Privileged Router# • Full privileges to read, write, modify, copy, and delete
• Examine interface status
• Examine router status
• Examine configuration file
• Change IOS and configuration file
Example:
Router> enable
password password
Router#
Configuration Router(config)# • Modify the active (running) configuration file
Example:
Router# configure terminal
Router(config)#
Password Configuration
Mode Location Syntax
User Console Port Router# configure terminal
Router(config)# line console 0
Router(config-line)# password string
Router(config-line)# login
User Auxiliary Port Router# configure terminal
Router(config)# line auxiliary 0
Router(config-line)# password string
Router(config-line)# login
User VTY Access Router# configure terminal
Router(config)# line vty 0 4
Router(config-line)# password string
Router(config-line)# login
Privilege (enable) N/A Router# configure terminal
Router(config)# enable password string
Privilege (secret) N/A Router# configure terminal
Router(config)# enable secret string
Copyright ©2005 Global Knowledge Network, Inc. All rights reserved. Page 12
Some Miscellaneous IOS Commands
Function Mode Syntax
Configure a Banner Config Router(config)# banner motd # banner #
Configure the router name Config Router(config)# hostname name
Examine the backup configuration in NVRAM Privileged Router# show startup-config
Examine the active configuration in RAM Privileged Router# show running-config
Display the contents of Flash memory User of Privileged Router> show flash
Save the active configuration to NVRAM Privileged Router# copy running-config startup-config
Restore the backup configuration to RAM Privileged Router# copy startup-config running-config
Save the active configuration to a TFTP Server Privileged Router# copy running-config tftp
Restore a configuration file from a TFTP Privileged Router# copy tftp running-config
Server
Write the current IOS out to a TFTP Server Privileged Router# copy flash tftp
Load a different IOS into the router Privileged Router# copy tftp flash
Erase the backup configuration from NVRAM Privileged Router erase startup-config
Boot using a different IOS in Flash Config Router(config)# boot system flash filename
Boot from a TFTP Server Config Router (config)# boot system tftp ip-address
filename
Configure the router as a TFTP Server Config Router(config)# tftp-server flash filename
Reboot the router Privileged Router# reload
Use the setup utility Privileged Router# setup
Display directly-connected Cisco neighbors User or Privileged Router> show cdp neighbor
Display the command history buffer User or Privileged Router> show history
Configure the length of the history buffer Privileged Router# terminal history size line-count
Display the current IOS, router run-time, User or Privileged Router> show version
amount of memory, and interfaces installed
Configure logout delay Line Config Router(config-line)# exec-timeout minutes
seconds
Configure clocking on a DCE interface Interface Config Router(config-if)# clock rate bps-value
Configure the bandwidth on an interface Interface Config Router(config-if)# bandwidth Kbps-value
Display the IP routing table User or Privileged Router> show ip route
Display the physical characteristics of an User or Privileged Router> show interfaces type number
interface
Display the logical characteristics of an User or Privileged Router> Show protocol interface type number
interface
Copyright ©2005 Global Knowledge Network, Inc. All rights reserved. Page 13
Enhanced Editing Commands
Function Syntax
Move to beginning of line Ctrl-A
Move to end of line Ctrl-B
Move back one word Esc-B
Move forward one word Esc-F
Move back one character Ctrl-B or left arrow
Move forward one character Ctrl-F or right arrow
Delete a single character Ctrl-D or backspace
Recall previous command (up in buffer history) Ctrl-P or up arrow
Move down through history buffer Ctrl-N or down arrow
IP Access Lists
Type Numbers Criteria Location
Standard 1 – 99 • Source IP address Close to the destination
Extended 100 – 199 • Source IP address Close to the source
• Destination IP address
• Source protocol number
• Destination protocol number
• Source port number
• Destination port number
Expanded Standard 1300 – 1999 • Expanded number range Close to the destination
Expanded Extended 2000 – 2699 • Expanded number range Close to the source
Named Alphanumeric string • Same as standard extended or Close to either destination or
extended source
Access List Syntax
Direction Description
Inbound • Interrogates packets as they arrive, before they are routed
• Can deny a packet before using CPU cycles to process it then deny it
Outbound • Interrogates packets after they are routed to the destination interface
• Packets can be discarded after they have been routed
• Default configuration when applying access lists to the interface
Copyright ©2005 Global Knowledge Network, Inc. All rights reserved. Page 14
Direction Description
Standard or Router(config)# access-list number permit or deny source-ip wildcard-mask
Expanded Standard • Number is in the range of 1-99, 1300-1999
• Each line either permits or denies
• Only examines the sources IP address from the IP packet
• Wildcard mask allows a single line to match a range of IP addresses
• Default mask is 0.0.0.0
• Wildcard mask of 0.0.0.0 is exact match of source IP address
• The word “host” can be substituted for the mask 0.0.0.0
• Wildcard mask of 255.255.255.255 means match every IP address
• The word “any” can be substituted for the mask 255.255.255.255
Extended or Router(config)# access-list number permit or deny source-ip source-mask operator source-port destination-ip
Expanded Extended destination-mask operator destination-port
• Number is in the range of 100 – 199, 2000 – 2699
• Each line either permits or denies
• Examines anything in the IP header: source and destination addresses, protocols, and ports
• Protocol can be IP, ICMP, IGRP, EIGRP, OSPF, UDP, TCP, and others
• Wildcard mask allows a single line to match a range of IP addresses
• Port numbers are optional and can only be entered if the protocol is UDP or TCP. Port numbers are in the range
of 1 – 65535
• A protocol of ICMP, the port numbers becomes an ICMP type code
• Operators are a Boolean function of gt, lt, neq, or range. LT is less than, GT is greater than, NEQ is not equal
to, and RANGE is a range of ports
• Boolean operators are only used with TCP or UDP
• Wildcard mask of 0.0.0.0 is exact match of source IP address
• The word “host” can be substituted for the mask 0.0.0.0
• Wildcard mask of 255.255.255.255 means match every IP address
• The word “any” can be substituted for the mask 255.255.255.255
Named Router(config)# access-list standard name
Router(config-std-nacl)# permit or deny source-ip wildcard-mask
or
Router(config)# access-list extended name
Router(config-ext-nacl)# permit or deny source-ip source-mask operator source-port destination-ip destination-
mask operator destination-port
• Same structure as Standard or Extended except alphanumeric string
Interface Router(config-if)# ip access-group number in or out
• Number is the access list being referenced; standard, extended, or named
• In or out specifies the direction of the frame flow through the interface for the access list to be executed. Out
is the default
Virtual Terminal (VTY) Router(config)# line vty vt# or vty-range
Router(config-line)# access-class number in or out
• Restricts incoming or outgoing vty connections for address in access list
• Number is the access list being referenced; standard, extended, or named
Copyright ©2005 Global Knowledge Network, Inc. All rights reserved. Page 15
Wildcard Masks
Mask Match Don’t Care Example
0.0.0.0 Every octet N/A 172.16.10.1 = 172.16.10.1
0.0.0.255 First three octets Last octet 172.16.10.1 = 172.16.10.0
0.0.255.255 First two octets Last two octets 172.16.10.1 = 172.16.0.0
0.255.255.255 First octet Last three octet 172.16.10.1 = 172.0.0.0
255.255.255.255 N/A Every octet 172.16.10.1 = 0.0.0.0
Network Address Translation – NAT
Function Syntax
Marks the interface as connected to the inside Router(config-if)# ip nat inside
Marks the interface as connected to the outside Router(config-if)# ip nat outside
Establishes static translation between an inside local Router(config)# ip nat inside source static local-ip global-ip
address and an inside global address
Defines a pool of global addresses to be allocated as Router(config)# ip nat pool start-ip end-ip {netmask netmask | prefix-length
needed prefix-length}
Establishes dynamic source translation to a pool based on Router(config)# ip nat inside source list access-list-number pool name
the ACL
Establishes dynamic source translation to a interface based Router(config)# ip nat source list access-list-number interface interface
on the ACL overload
Displays active translation Router# show ip nat translations
Displays translation statistics Router# show ip nat statistics
Clears all dynamic address translation entries Router# clear ip nat translation *
Clears a simple dynamic translation entry that has an inside Router# clear ip nat translation inside global-ip local-ip [outside local-ip
translation or both inside and outside translation global-ip]
Clears a simple dynamic translation entry that has an out- Router# clear ip nat translation outside local-ip global-ip
side translation
Clears an extended dynamic translation entry Router# clear ip nat translation protocol inside global-ip global-port local-ip
local-port [outside local-ip local-port global-ip global-port]
WAN Connection Types
Connection Definition
Leased Line • A pre-established, private connection from one site to another through a provider’s network
• Also called a dedicated circuit or a dedicated connection
• Always a point-to-point connection between two end points
• Used when there is a constant flow of data, or when a dedicated amount of bandwidth is required
• One router interface is connected to one destination site
• Examples – PPP, HDLC
Copyright ©2005 Global Knowledge Network, Inc. All rights reserved. Page 16
Connection Definition
Circuit Switching • A dial-up connection through a provider’s voice-grade network
• Either uses an analog modem or an ISDN connection
• Used when only a slow-speed connection is needed, or when there is not much of a need to transfer a
lot of data
• One call establishes a circuit to one destination site
• Examples – PPP, HDLC, SLIP
Packet Switching • Each site only uses one physical connection into the provider’s network, however there may be multiple
virtual circuits to various destinations
• Typically less expensive than leased lines, because you are mixing various data streams across a single link
• Used when a dedicated connection is needed, but cost savings is important
• Examples – Frame Relay, X.25
Cell Switching • Each site only uses one physical connection into the provider’s network, however there may be multiple
virtual circuits to various destinations
• Typically less expensive than leased lines, because you are mixing various data streams across a single link
• Uses fixed-size packets called cells to achieve faster and more predicable transport through the network
• Examples – ATM, SMDS
High-Level Data Link Control • A Cisco-proprietary serial encapsulation
(HDLC) • Allows multiple network-layer protocols to travel across
• Default encapsulation for all serial interfaces on a Cisco router
• One router interface only goes to one destination
Point-to-Point Protocol (PPP) • An open-standard serial encapsulation
• Allows multiple network-layer protocols to travel across
• Allows optional link-layer authentication (CHAP or PAP)
• One router interface only goes to one destination
Serial Line Internet Protocol • An open-standard serial encapsulation
(SLIP) • Allows only IP to travel across
• One router interface only goes to one destination
Frame Relay • A very popular packet switching standard
• Uses switched virtual circuits (SVCs) or permanent virtual circuits (PVCs)
• Allows multiple network-layer protocols to travel across
• Each virtual circuit is a private channel between two end points
• One router interface may have many virtual circuits, going to the same location or various locations
X.25 • An old, but still available, packet switching standard
• Uses switched virtual circuits (SVCs) or permanent virtual circuits (PVCs)
• Allows multiple network-layer protocols to travel across
• Each virtual circuit is a private channel between two end points
• One router interface may have many virtual circuits, going to the same
Copyright ©2005 Global Knowledge Network, Inc. All rights reserved. Page 17
Popular WAN Terms
Term Definition
Customer Premise Equipment • Network devices/equipment physically located at the customer’s location/site
(CPE) • Customer is typically required to procure/maintain this equipment
• Equipment could include routers and CSU/DSUs
Central Office (CO) • The facility that provides WAN services to the customer
• Source of analog phone service, ISDN service, DSL service, frame relay connections, X.25 connections,
and leased lines
Local Loop • The link from the provider’s CO to the customer’s demarc
• Also called the “last mile”
• Normally not more than a few miles
Demarcation Point (Demarc) • The line between the customer site and the provider network
• Inside of the demarc is the CPE
• Outside of the demarc is the local loop
Toll Network • The provider’s network
• Inside the WAN cloud
• Typically “smoke and mirrors” to a customer
ISDN Device Types
Device Function
Network Termination 1 (NT-1) Converts BRI signals into a form used by the ISDN digital line
Network Termination 2 (NT-2) The aggregation point of ISDN services at a customer site
Terminal Adapter (TA) Converts analog signals into BRI signals
Terminal Endpoint 1 (TE-1) A devices that has an ISDN interface, such as a router
Terminal Endpoint 2 (TE-2) A device that does not have any ISDN interfaces and requires a TA to access the ISDN network, such as a PC
ISDN Reference Points
Reference Point Function
R The point between a non-ISDN device and the TA
S The point between the TA and the NT-2, or between ISDN devices and the NT-2
T The point between the NT-2 and the NT-1
U The point between the NT-1 and the ISDN provider
ISDN Protocols
Reference Point Function
E-series Recommend telephone network standards
I-series Deal with concepts, terminology, and general methods used within ISDN
Q-series Cover switching and signaling through the ISDN cloud
Copyright ©2005 Global Knowledge Network, Inc. All rights reserved. Page 18
ISDN Interface Types
Interface Type Characteristics
Basic Rate Interface (BRI) • 2 Bearer (B) channels, 64 Kbps data each
• 1 control channel (D), 16 Kbps
Primary Rate Interface (PRI) • 23 Bearer (B) channels, 64 Kbps data each – across a T1 circuit, typically seen in North America and Japan
• 30 Bearer (B) channels, 64 Kbps data each – across an E1 circuit, typically seen in Australia and Europe
• 1 control channel (D), 64 Kbps
Sample ISDN Commands
Function Mode Syntax
Configure the ISDN switch config Router(config)# isdn switch-type switch
type • switch types include basic-dms100, basic-5ess and basic-ni
Create a static route config Router(config)# ip route network mask destination-ip
• network is the other side of the ISDN cloud, since there is no dynamic routing protocol running
across the ISDN network
• mask is the subnet mask to specify the distant network
• destination-IP is the IP address of the BRI interface of the remote site
Create a dialer list config Router(config)# dialer-list number protocol protocol permit
• number can be from 1 – 10
• protocol can be any protocol, such as IP or IPX
Access the BRI interface config Router(config)# interface bri number
Assign SPID numbers interface Router(config-if)# isdn spid1 spid-number
config • spid-number is the logical circuit ID assigned by the ISDN provider
• there might be two SPID numbers, thus the second one would be referenced as “spid2”
Reference the dialer list interface Router(config-if)# dialer-group number
config • number is the dialer list created earlier
Create a map to point to and interface Router(config-if)# dialer map protocol destination-ip dial-number
dial the remote site config • protocol is the protocol being mapped across the ISND cloud, such as IP or IPX
• destination-IP is the IP address of the BRI port on the other side of the ISDN cloud, specified by
the static route
• dial-number is the ISDN phone number of the remote site
Frame Relay Terms
Term Definition
Local Access Rate Connection rate between a frame relay site and the frame relay provider. Many virtual circuits run across
a single access point.
Virtual Circuit Logical connection between two end points
• Permanent Virtual Circuit (PVC) – the circuit is always available, and the bandwidth for the circuit is
always allocated
• Switched Virtual Circuit (SVC) – the circuit is built when needed, and the bandwidth is returned when
the circuit is closed
Copyright ©2005 Global Knowledge Network, Inc. All rights reserved. Page 19
Term Definition
Data Link Connection Identifier The local reference to one end of a virtual circuit. The DLCI numbers are assigned by the frame relay
(DLCI) providers.
Committed Information Rate The maximum allowed bandwidth through the PVC from one end to the other. Each PVC can have a
(CIR) unique CIR.
Inverse Address Resolution The process of a frame relay device, such as a router, discovering the network-layer information about the
Protocol (IARP) devices at the other end of the PVCs.
Local Management Interface Signaling between the frame relay device (the router) and the frame relay switch (the provider). LMI does
(LMI) not travel across the entire PVC from one end to the other.
Sample Frame Relay Commands
Function Mode Syntax
access the serial interface config Router(config)# interface serial number
change the encapsulation interface Router(config-if)# encapsulation frame-relay option
config • option can either be Cisco (default) or ietf (open standard)
specify the LMI type interface Router(config-if)# frame-relay lmi lmi-type
config • lmi-type can be Cisco, ansi, or q933a
• this command is normally not needed, as the router will automatically sense the LMI type if
configured by the provider
assign the local DLCI interface Router(config-if)# frame-relay interface-dlci local-dlci
config • local-dlci is the DLCI number of the PVC that terminates on this interface. There can be more
than on DLCI on an interface.
• this command is not needed with a major interface, since the router will automatically retrieve
the DLCIs from the frame relay switch.
create a sub-interface config Router(config)# interface serial number.sub point-to-point or multipoint
• point-to-point defines a subinterface that will only have one DLCI (interface-dlci command)
• multipoint defines a subinterface that may have more than one DLCI (interface-dlci command)
create a static map interface Router(config)# frame-relay map protocol destination-IP local-dlci
config • protocol is the protocol being mapped across the frame relay cloud, such as IP or IPX
• destination-IP is the IP address of the frame relay interface at the other end of the PVC
• local-DLCI is the local DLCI needed to access the remote site
• this command is not needed if inverse-ARP is properly configured, and the interface-dlci com-
mand is used
Configuration Register
8 4 2 1 8 4 2 1 8 4 2 1 8 4 2 1 binary weight
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 bit position
0 0 1 0 0 0 0 1 0 0 0 0 0 0 1 0 bits set
2 1 0 2 hex value
Copyright ©2005 Global Knowledge Network, Inc. All rights reserved. Page 20
