Ccna Imp Guide

CCNA Cram Guide A Presentation by Faruk Mamaniat (mrlogic0) Based on Paul Browning’s “CCNA Cram Guide”

CCNA Cram Guide

1. OSI Model

7. Application Layer

Provides Services to lower layers

Enables program to program communication

Determines if sufficient resources exist for communication

Examples:

Email gateways (SMTP)

FTP

TFTP

SNMP

6. Presentation Layer

Presents information to the Application layer.

Compression

Data conversion

Encryption

Standard formatting occurs here.

Contains data formats:

JPEG

MPEG

MIDI

TIFF

[Encapsulation = data]

5. Session Layer

Establishes and maintains communication ‘sessions’ between applications (dialogue control)

Sessions can be:

Simplex (one direction only)

Half-duplex (one direction at a time)

Full duplex (both ways simultaneously)

Keeps different applications' data separate from other applications

Protocols include:

NFS

SQL

X Window

RPC

ASP

NetBIOS Names

[Encapsulation = data]

4. Transport Layer

Responsible for end to end integrity of data transmissions

Establishes a logical connection between sending and receiving hosts via ‘virtual circuits’

Windowing works at this level to control how much information is transferred before acknowledgement is required

Data is segmented and reassembled at this layer

Port numbers are used to keep track of different conversations crossing the network at the same time

Error correction (not detection)

Supports:

TCP

UDP

SPX

NBP

[Encapsulation = segments]

3. Network Layer

Routes data from one node to another and determines the best path to take

Routers operate at this level

Network addresses are used here for routing

Routing tables, subnetting and control of network congestion occur here.

Routing protocols regardless of which protocol they run over reside here:

RIP

IP

IPX

ARP

IGRP

Appletalk

[Encapsulation = Packets]

2. Data Link Layer

Sometimes referred to as the LAN layer .

Responsible for the physical transmission of data from one node to another

Packets are translated into Frames here and hardware address is added.

Error detection

Bridges and switches operate at this layer.

[Encapsulation = Frames]

Data Link Sublayers

Logical Link Control (LLC) 802.2:-

Manages communications between devices over a single link on a network

Uses Service Access Points (SAPs) to help lower layers talk to the Network Layer.

Media Access Control (MAC) 802.3:-

Builds frames from the 1’s and 0’s that the Physical Layer (address = 6-byte/48 bit) picks up from the wire as a digital signal

Runs a Cyclic Redundancy Check (CRC) to assure no bits were lost or corrupted.

1. Physical Layer

Puts data onto the wire and takes it off

Physical layer specifications such as:

Connectors

Voltage

physical data rates

DTE/DCE interfaces

Some common implementations include:

Ethernet/IEEE 802.3

Fast Ethernet

Token Ring/IEEE 802.5

[ Hubs operate here]

[Encapsulation = Bits]

2. Cisco Hierarchical Model

Core Layer

Switch traffic as quickly as possible

Fast transport to Enterprise services (internet etc).

No packet Manipulation, VLANs or access-lists

High speed access required such as FDDI, ATM

Distribution Layer

Time sensitive manipulation such as routing, filtering and WAN access

Broadcast/Multicast, media translations, security

Access Layer

Switches and routers

Static (not dynamic) routing

[Network] Segmentation occurs here

Workgroup access

3. Port Numbers

Common port numbers are:

20 - File Transfer Protocol – Data (TCP)

21 - File Transfer Protocol – Control (TCP) (Rarely Used)

22 - SSH (TCP)

23 - Telnet (TCP)

25 - Simple Mail Transfer Protocol (TCP)

53 - Domain Name Service (TCP/UDP)

69 - Trivial File Transfer Protocol (UDP)

80 - HTTP/WWW (TCP)

110 - Post Office Protocol 3 (TCP)

119 - Network News Transfer Protocol (TCP)

123 - Network Time Protocol (UDP)

161/162 - Simple Network Management Protocol (UDP)

443 - HTTP over Secure Sockets Layer (TCP)

4. TCP/IP & UDP

TCP – (protocol 6)

Reliable, sequenced Connection-oriented delivery

20-byte header.

UDP – (protocol 17)

Connectionless, Unsequenced, best effort delivery

6-byte Header.

Sends data but does Not check to see if it is received.

Services/Protocols

Telnet

Used to connect to a remote device (TCP)

A password and username is required to connect.

Telnet tests all seven layers of the OSI model.

SNMP

Allows remote management of network devices.

Services/Protocols

FTP

Connection orientated (TCP) protocol

Used to transfer large files.

TFTP

Connectionless (UDP) protocol used for file transfer

ICMP

ICMP

Supports packets containing error, control and informational messages.

Ping uses ICMP to test network connectivity.

ARP

Used to map an IP address to a physical (MAC) address.

A host wishing to obtain a physical address broadcasts an ARP request onto the TCP/IP network.

The host replies with its physical address.

DNS

Resolves hostnames to IP addresses (not the other way around).

To configure the router to use a host on the network use the command:

ROUTER(config)#ip nameserver 4.2.2.2

To configure DNS the command: ‘ip Name-server’ is usually already turned on for the router config by default.

If you want hosts on the network to use the router as a proxy DNS server put this command onto the router:

ROUTER(config)#ip dns server

DHCP

Involves a central server or device which relays TCP information to hosts on a network.

You can configure a router to be a DHCP server with the below config

Must have hosts on the same LAN as the router interface:

ROUTER(config)#ip dhcp pool E00_DHCP_Pool

ROUTER(dhcp-config)#network 10.10.10.0 255.255.255.0

ROUTER(dhcp-config)#dns-server 24.196.64.39 24.196.64.40

ROUTER(dhcp-config)#domain-name mydomain.com

ROUTER(dhcp-config)#default-router 10.10.10.254

ROUTER(dhcp-config)#lease 1

5. Cisco IOS

6 Modes:

User EXEC:- Router>

Privileged EXEC:- Router#

Global Configuration:- Router(config)#

ROM Monitor:- > or rommon>

Setup:- series of questions

RXBoot:- Router<boot>

Editing Commands (1):

Ctrl+W - Erases a word

Ctrl+U - Erases a line

Ctrl+A - Moves cursor to beginning of line

Ctrl+E - Moves cursor to end of line

Ctrl+F - (or right arrow) – Move forward one character

Ctrl+B - (or left arrow) – Move back one character

Ctrl+P - (or up arrow) – Recalls previous commands from buffer

Ctrl+N - (or down arrow) – Return to more recent commands in buffer

Esc+B - Move back one word

Esc+F - Move forward one word

Editing Commands (2):

Tab - completes a command you have started:

Router# copy ru <- press tab key after the ‘u’

Router# copy running-configuration

? gives you the command options:

Router#copy ?

Flash: Copy from flash: file system

Ftp: Copy from ftp: file system

Nvram: Copy from nvram: file system

Running-config Copy from current system configuration

Startup-config Copy from startup configuration

System: Copy from system: file system

Tftp: Copy from tftp: file system (truncated to save space)

Or the commands beginning with the letters you have typed:

Router#a?

Access-enable

access-profile

access-template

6. Router Elements

DRAM (1)

Working area for router.

Contains:

Routing tables

ARP cache

Packet buffers

IOS

Running config

Some routers run the IOS from DRAM.

DRAM (2)

Show version

Shows information about IOS in RAM

Displays how much physical memory is installed

Shows the config register setting.

Show process

Shows info about programs running in DRAM.

Show running-configuration

Shows active configuration in DRAM

Show memory/stacks/buffers

To view tables and buffers

NVRAM

Stores router's start up configuration

Does not lose data when powered off (due to a battery power source.)

Show startup-configuration

Erase startup-configuration

Copy running-configuration startup-configuration (copy run start)

Config register 0x2142 skips start up config file in NVRAM (for password recovery)

Config register 0x2102 loads start up config files from NVRAM

Flash

(EEPROM or PCMCIA card) holds the compressed operating system image (IOS)

This is where software upgrades are stored.

Show flash

Dir flash:

ROM

Contains power on diagnostics, a bootstrap program and a mini IOS (rommon).

You can specify which file the router boots from if you have more than one in flash memory

Router(config)#boot system flash {IOS filename}

Or that it boots from a TFTP server if for example the image is too large to fit in flash.

Router(config)#boot system tftp {IOS filename}{tftp address)

You can also back up the flash image for emergency use.

Router(config)#copy flash tftp

7. Cabling

Pinouts

Crossover

1 <-> 3

2 <-> 6

3 <-> 1

6 <-> 2

Straight Through 1 <-> 1 2 <-> 2 3 <-> 3 4 <-> 4 5 <-> 5 6 <-> 6 7 <-> 7 8 <-> 8 Rollover (PC to Console/Aux port) 1 <-> 8 2 <-> 7 3 <-> 6 4 <-> 5 5 <-> 4 6 <-> 3 7 <-> 2 8 <-> 1

Two types of crosstalk can occur on twisted pair cables:

Near end crosstalk (NEXT)

Far end crosstalk (FEXT)

8. Router Management

Router Management

Console port:

A PC is connected to the console port via a rollover cable.

Used for initial configuration or disaster recovery.

Auxiliary port:

Normally a modem connected to this port.

Virtual Terminals:

Normally accessed by telnetting to the router.

Five lines available numbered [vty] 0-4

Router Management

TFTP server:

The router can get its configs or IOS from a server (PC for example) running TFTP software and holding the necessary files.

NMS:

Network management station

Uses SNMP to manage the router normally via a Web style interface.

9. CDP

Router#show cdp neighbors

This command displays the neighbouring router or switches hostname, hardware platform, port identifier and capabilities list.

Router#show cdp neighbors detail

This command displays more detail than the previous one. You can view IP address, IOS release and duplex setting.

10. LAN Switching

A LAN switch has three primary functions:

1. Address Learning

Maintains a table (CAM – Content Addressable Memory) of addresses and which port they can be reached on.

2. Forward/filter decision

Forwards frames only out of the relevant port.

3. Loop avoidance

STP

Transmitting Frames Through a Switch

Store-and-Forward

Switch copies the entire frame into its buffer and computes the CRC

Frame is discarded if there is an error.

High latency.

Cut-through

Reads only the destination address (first 6 bytes after preamble), looks up address and forwards frame.

Lower latency.

Fragment free

Switch reads first 64 bytes before forwarding the frame.

(Collisions normally occur within the first 64 bytes.)

Spanning Tree Protocol (STP) IEEE 802.1d

A link management protocol that provides path redundancy whilst preventing undesirable loops in the network

For communication to work correctly on an ethernet network there can only be one path between two destinations.

STP uses Bridge Protocol Data Units (BPDU) received by all switches to determine the spanning-tree topology.

A port on a switch is either in forwarding or blocking state.

Forwarding ports provide the lowest cost path to the root bridge

A port will remain in blocking state from start up if spanning tree determines there is a better path.

Rapid Spanning Tree Protocol (RSTP) IEEE 802.1w

Spanning tree takes up to 50 seconds to converge to a stable network whereas RSTP takes 2 seconds.

RSTP port roles are:

Root Port

Designated Port

Backup Port

Alternate Port

Disabled

Most implementations of RSTP use PVST+ (Per VLAN Spanning Tree+):

Multiple instances of Spanning Tree are running so the load on the CPU is higher but we can load share over the links.

To enable RSTP for each VLAN in our switched network we use the following command:

Switch(config)#spanning-tree mode rapid-pvst

Bridging & Switching

Switching

LAN Switches are primarily hardware based.

Many spanning-tree instances per switch and up to 100 ports.

Bridging

Bridges are primarily software based and have one spanning-tree instance per bridge.

Normally 16 ports per bridge.

Virtual LAN (VLAN)

A VLAN is a switched network that consists of logically segmented communities without regard to physical location.

Each port on a switch can belong to a VLAN.

VLAN ports share broadcasts.

A router is needed to route traffic between VLANs because layer 2 devices do not use IP addresses.

Reduces admin costs, tighter security and better control of broadcasts.

11. IP Addressing

Class A

Format/Default Mask

N . H.H.H

255.0.0.0

Leading Bit Pattern = 0

Network Address Range = 0 - 126

Max Networks = 126

Max Hosts/nodes = 16,777,214

Class B

Format/Default Mask

N.N. H.H

255.255.0.0

Network Address Range = 128 -191

Max Networks = 16,384

Max Hosts/nodes = 65,534

Class C

Format/Default Mask

N.N.N. H

255.255.255.0

Max Networks = 2,097,152

Max Hosts/nodes = 254

Class D

Multicast

Class E

Experimental

12. Subnetting

13. IPv6

The two methods of migrating from IPv4 to IPv6 are:

Dual-Stack

Tunnelling

14. IP Routing

Static routing:

Router(config)#ip route {destination network}{mask}{next hop address}

E.g

ip route 172.16.5.2 255.255.255.0 172.16.12.8

Dynamic addressing is done by using a routing protocol:

For RIP v2

Router(config)#router rip

Router(config-router)#version 2

Router(config-router)#network 172.16.0.0

Router(config-router)#no auto-summary <- {optional}

For EIGRP

Router(config)# router eigrp 20

Router(config-router)#network 172.16.0.0

Router(config-router)#no auto-summary <- {optional}

For OSPF

Router(config)#router ospf 20

Router(config-router)#network 172.16.0.0 0.0.255.255 area 0

Distance Vector (1)

Distance Vector protocols understand the direction and distance to any given network connections.

Algorithms calculate the cost to reach the connection and pass this information to every neighbour router.

Examples are RIP and IGRP.

Problems:

Routing loops

Counting to infinity

Distance Vector Solutions:

Defining a maximum number of hops:

RIP = 15

IGRP = 255

Split Horizon

If the router learns a route on an interface do not advertise it out of the same interface.

Route Poisoning

Information passed out of an interface is marked as unreachable by setting the hop count to 16 (for RIP).

Hold Down Timers

Ignores new routing updates until a determined time has passed.

Triggered Updates

Instead of routing updates being sent at the default intervals; a triggered update is sent every time to indicate a change in the routing table.

Link state (1)

These have a picture of the entire network from link state advertisements (LSA) and link State packets (LSP). Once these have all been passed only changes to the network are sent out reducing network traffic.

Req a lot of CPU time & b/width when LSAs are flooded eg:

OSPF

IS-IS

Routers use administrative distances to determine how believable the route learned is depending upon the protocol it learns the router from:

Routers prefer lowest distance eg:

Direct connection (0) >> OSPF (110) >> RIP (120)

Install this protocol in routing table

Link state (2)

Routing Protocols

Maintain table of hosts

Which i/face they can be reached by

Eg: RIP, OSPF

Routed Protocols

Used to transport traffic from source to destination

Eg: IP, IPX, AppleTalk

When a packet traverses a n/work from device to device (hop to hop):

IP address = constant

MAC address changes

Source - Default Distance:

Directly Connected Interface = 0

Static hop to next router = 1

EIGRP Summary = 5

External BGP = 20

EIGRP (Internal) = 90

OSPF = 110

IS-IS = 115

RIP = 120

Exterior Gateway Protocol (EGP) = 140

External EIGRP = 170

Internal BGP = 200

Unknown = 255

15. Routing Protocols

RIP v2

Uses UDP port 520

Classless

Max hop count 15

Multicasts route updates to 224.0.0.9

Supports authentication

Update timer 30 seconds

Invalid 90 seconds

Hold down 180 seconds

Flush 270 seconds

EIGRP

Uses IP protocol 88

Classless

Hybrid of distance vector and link state

Multicasts updates to 224.0.0.10

Uses feasible successors to determine alternative routes to networks.

The feasible successor is a backup route based upon the topology table.

OSPF

Uses IP protocol 89

Classless

Uses Dijkstras shortest path algorithm (SFP)

Router ID is the highest IP address but loopback address used if present

Backbone area is area 0

All non backbone areas must connect directly to area 0

Areas can be numbered from 0 to 65535

Multicasts on 224.0.0.5

OSPF Interface / Cost:

OSPF uses cost as a metric (see below - * indicates the most common) [Cost (10^8/Bandwidth)]

ATM, Fast Ethernet, Gigabit Ethernet, FDDI (> 100 Mbps) = 1

HSSI (45Mbps) = 2

16 Mbps Token Ring = 6

10 Mbps Ethernet = 10

4 Mbps Token Ring = 25

T1 (1.544 Mbps)* = 64

DS-0 (64k)* = 1562

56k = 1785

16. NAT

NAT Facts

Converts internal address to external address commonly:

Convert non-routable address to routable address

For all configs you must specify internal & external i/faces

Router(config-if)#ip nat inside/outside

Static NAT

Maps one address to another address such as 192.168.1.1 to 200.1.1.1

Router(config)#ip nat inside source static 192.168.1.1 200.1.1.1

Dynamic NAT

Maps a number of internal addresses to a pool of external addresses.

Example config:

1. Creates a pool of 10 addresses with a mask (prefix length) of 255.255.255.0 and the name ‘ad_team.’

2. The hosts to be NATted are on the 192.168.1.0 network.

3. The Access list (source list) tells the router which addresses to NAT.

Router(config)#ip nat pool ad_team 10.0.0.1 10.0.0.10 prefix-length 24

Router(config)#ip nat inside source list 1 pool ad_team out

Router(config)#access-list 1 permit 192.168.1.0 0.0.0.255

Overload NAT (PAT)

Maps private internal addresses to one or more external addresses using port nos

Example config:

Creates a pool of ten addresses (it could be more)

The command ‘overload’ tells the router to use port address translation.

Router(config)#ip nat pool ad_team 10.0.0.1 10.0.0.10 prefix-length 24

Router(config)#ip nat inside source list 1 pool ad_team out overload

Router(config)#access-list 1 permit 192.168.1.0 0.0.0.255

17. Wireless Networks

Ad-hoc Mode

Similar to peer-to-peer networking where nodes connect directly to each other

They must have the same SSID and channel for this to work.

Infrastructure Mode

W/less clients connect to access point (AP)

BSS (Basic Service Set)

1 access point and multiple clients

ESS (Extended Service Set)

2 or more BSSs

W/less Security

Open System

Host sends an association request to the wireless access point and it will be sent a success or failure message

Shared key

A key or pass phrase is configured on the AP & client(s)

3 Types of Authentication: WEP, WPA, WPA2…

3 Types of Authentication:

WEP

An encryption algorithm built in the 802.11 standard

RC4 40bit or 104 bit key

24-bit IV (Initialization Vector)

WPA

Uses dynamic key management

Adds a stronger encryption cipher

Built on the EAP/802.1X mechanism

Uses TKIP (Temporal Key Integrity Protocol)

48-bit IV

Used w/ RADIUS in the Enterprise

WPA2

Next generation

Uses stronger AES (Advanced Encryption Standard)

Creates a new key for every new association

Client's keys are unique & specific to that client

18. Network Security

Access Lists

A set of conditions that permit or deny access to or through a router's i/face

Inbound Access Lists

Outbound Access Lists

Can be applied to multiple interfaces

There can only be one access list per protocol per direction per interface

Wildcard masks

Access lists are applied to interfaces

Range <<>> Usage

Standard Access Lists

Extended Access Lists

Named Access Lists

‘ access-class’

Used if applying to console/aux/vty lines

Show ip access-lists

Show access-list 1

Packets are processed by the access list and then routed.

Inbound & Outbound Access Lists

Inbound:

Save the router having to process the packet

Denied packets will be dropped at the inbound interface

Outbound:

Will be processed by the router

Then dropped at the outbound interface if they match the access list

Wildcard masks

Tell the router which parts of the address to look at and which to disregard

Access-list 12 permit 172.16.5.0 0.0.0.255

This would permit any host on network 172.16.5.x

Access lists are applied to interfaces:

Router(config)#access-list 1 permit 172.16.5.2

Router(config)#interface e0

Router(config-if)#ip access-group 1 in

Range <<>> Usage

1300-1999 >> IP Standard (Expanded Range)

100-199 >> IP Extended

1-99 >> IP Standard

2000-2699 >> IP Extended (Expanded Range)

Standard Access Lists

Check only the source address of the packet & permits or denies entire TCP/IP suite

You cannot choose a particular port or application to block

Cisco recommends that they are placed as close to the destination as possible.

Router(config)#access-list{number 1-99}{permit/deny}{source address}

Access-list 10 permit 172.16.5.2 <<- address can be a host or network

Extended Access Lists

Allow for a lot more granularity when filtering IP traffic.

Can filter traffic based upon:

Source or destination

A particular IP protocol

Port number

Cisco recommends that they are placed as close to the source as possible.

Router(config)#access-list {number 100-99}{permit/deny}{protocol}

Access-list 112 permit tcp host 172.16.5.2 host 172.16.10.2 eq www

Named Access Lists

Router(config)#ip access-list {standard/extended} name

Router(config)#ip access-list extended no_ftp

Passwords

Service password-encryption

Enable

Enable Secret

VTY

Auxiliary

Console

Password cont…

Service password-encryption

Encrypts all passwords

Enable

Used to get from user exec to privileged exec.

Not encrypted

Router(config)# enable password {password}

Enable Secret

Encrypts password

Router(config)# enable secret {password}

(only use enable or enable secret not both)

Password cont…

VTY

Needed if telnet access is required

Router(config)#line vty 0 4

Router(config-line)#password cisco

Router(config-line)#login

Auxiliary

Allows modem access to the aux port

Router(config)#line aux 0

Console

Used to allow console access

Router(config)#line console 0

Protecting the Network

Firewalls

Divide your network into three zones:

Trusted

Semi-Trusted

Un-Trusted

VPN

Allows information to be sent securely over an insecure medium (eg Internet)

Can be:

Site-to-Site (eg WAN)

Access (eg homeworker)

Security Device Manager (SDM)

A GUI web based tool

Allows you to configure and manage your Cisco routers

Can be installed on your router or your PC

(Huge amount of parameters and screens to navigate)

19. Wan Protocols and Services

HDLC

Cisco default on serial WAN connections

No authentication available

PPP

Data link

Authentication is optional:

PAP (clear text)

CHAP (secure hash)

Use PPP if connecting a Cisco router to a non-cisco router.

Router(config)#hostname paul password cisco <<- case sensitive

Router(config)#interface serial 0

Router(config-if)#encapsulation ppp

Router(config-if)# ppp authentication chap

Frame Relay (1)

Based upon x.25 protocol

Less error checking = quicker

56K to 2Mb

Ideal for SMEs

Works at the physical & data link layers.

DLCI’s are used to identify the circuit

Frame Relay (2)

Each router uses LMIs for keepalives on the line between the router & the frame relay switch:

LMI type is Cisco by default.

You must use another type such as ansi if connecting to a non-cisco router.

Router(config-if)#encapsulation frame-relay Router(config-if)#frame-relay map ip 2.2.2.2 100

Router is told to get to ip address 2.2.2.2 use dlci 100

Use frame relay sub-interfaces if point-to-point or multipoint connection is needed

IP address applied to sub-interfaces for these and NOT the main interface

Frame relay uses:

Backwards Explicit Congestion Notification (BECN)

On returning frames to warn of congestion

Forward Explicit Congestion Notification (FECN)

Is set by the DCE end to warn of congestion from the sending end.

Frame Relay Problems include:

Incorrect LMI setting

Incorrect DCLI

Split horizon preventing routing updates leaving interface

20. Troubleshooting

Show ip interface brief

First command to issue to establish if the interfaces are up or down

(There are only a handful of ways to break any network in the exam.)

Layer 1

Ensure that there is a clock rate on the DCE interface

Show controllers serial X

To check what type of cable is attached

X = serial i/face no

Ensure that the ‘ no shut ’ command has been applied to the interface.

Layer 2

Ensure that the correct encapsulation type is on the interface i.e. HDLC, PPP etc

Show interface serial X

If it is not then go into interface configuration mode and change it.

Layer 3

Ensure that the correct IP address AND subnet mask is applied to the interface.

Ensure that the correct networks are being advertised by the routing protocol

Show ip protocols

Warning!

Always ensure that you can ping across directly connected router interfaces BEFORE applying routing protocols and access lists.

CCNA Cram Guide

Ccna Imp Guide

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