CCNA 6.3 Configuring IP Routing

• When a router receives a packet for a network that isn't listed in the router, it would just discard the packet.
• Static Routing benefits': No overhead on router CPU, No bandwidth usage between routers & security
• Static Routing disadvantages': Not feasible in large network,
• Static Route command syntax:

ip route [destination_network] [mask] [next-hop address / exitinterface] [administrative_distance] [permanent]

• Default routing sends packets with a remote destination network not in the routing table to the next-hop router

CCNA 6.2 IP Routing Process

• Packets destined for remote networks must go through the default gateway. (frame can't be placed on remote networks)

CCNA 6.1 Routing Basics

• Static routing means that administrator must manually input all network locations into the routing table
• Dynamic routing means that routers within the known networks automatically updates their routing table whenever there is a change

CCNA 5.9 Checking Network Connectivity & Troubleshooting

• Ping and traceroute command can be used to test connectivity to remote device (user & privileged mode)
• Ping command displays the min, avg & max times for a ping packet to reach a specific remote device and return
• Traceroute command shows the path a packet takes to reach a remote device
• Debug command is used to display router operation, traffic and error message (privileged mode)
• Show processes command show router's CPU utilization info

CCNA 5.8 Resolving Hostnames

• In order to use hostname to connect to a remote device, local device must be able to resolve hostname to IP addresses
• Host table on each router & DNS server can be used to resolve hostname

CCNA 5.7 Using Telnet

• In order to use telnet, VTY passwords has to be set on remote router
• Pressing Ctrl+Shift+6 key , then X key allows user to telnet into multiple devices simultaneously
• Show sessions command allows user to observe telnet connection made from user's router to a remote device
• Show users command allows user to list all active console and VTY ports in use on user's router
• Exit / disconnect command allows user to end a Telnet session

CCNA 5.6 Cisco Discovery Protocol (CDP)

• CDP is a proprietary protocol designed to help administrators collect information about both locally attached and remote devices
• Show cdp command gives user info on CDP timer & holdtime
• CDP timer is how often CDP packets are transmitted out all active interfaces
• CDP holdtime is the amount of time that the device will hold packets received from neighbor devices
• show cdp neighbors command deliver info (device ID, local interface, holdtime, capability, platform & port ID) about locally connected devices
• show cdp neighbors detail command deliver extra info on IP address & IOS version
• show cdp traffic command displays info about interface traffic (amount of CDP packets sent & received)
• show cdp interface command display info about CDP status on router interfaces or switch ports

CCNA 5.5 Backing Up and Restoring Cisco Configuration

• Cisco router configuration can be back up & restored through TFTP, Cisco IFS & SDM
• Changes on router configuration are stored in running-config file
• Router config changes will be lost when router is reboot or powered down (if it is not copy to startup-config)
• Copy running-config tftp command is used to copy router's configuration from a router to TFTP server
• Copy tftp running-config command is used to restore router's configuration from a TFTP server to a router

CCNA 5.4 Backing up and restoring Cisco IOS

• Cisco IOS can be back up & restored through TFTP, Cisco IFS & SDM
• Before upgrading IOS, user have to verify router flash memory space through show flash or show version command
• Copy flash tftp command is used to backup Cisco IOS to a TFTP server
• Copy tftp flash command is used to restore or upgrade Cisco IOS from a TFTP server
• Cisco IOS File System (IFS) allows user to work with files and directories through Windows DOS prompt

CCNA 5.3 Managing Configuration Register

• All Cisco routers have a 16-bit software register (Configuration) in NVRAM
• Configuration register loads IOS from flash memory and startup-config file from NVRAM
• Default configuration setting on Cisco router is 0x2102

• 0x means that the digits that follow are in hexadecimal
• Software configuration meaning:

• Boot Field:

• Show version command can be used to check current value of configuration register
• Configuration register value can be changed to modify how the router boots and runs
• Config-register command can be used to change config register value
• To recover a router password, user have to turn on bit 6 (0x2142) of configuration register to ignore the NVRAM contents (start-up config)
• Ctrl +Break key is used to interrupt boot sequence and enter ROM monitor mode
• I command is used to reset the router
• boot system command allows user to tell router which file to boot from flash memory
• Cisco's suggested IOS backup routine: flash, TFTP host, ROM

CCNA 5.2 Router Boot Sequence

1. Perform POST to test hardware components' functionality (stored in ROM)
2. Bootstrap loads IOS from flash memory
3. IOS searches for valid config file (startup-config) in NVRAM
4. Router copies startup-config file from NVRAM to RAM and named it running-config file

CCNA 5.1 Internal Components of Cisco Router

• Cisco Router Components:

CCNA 4.6 Cisco Security Device Manager (SDM)

• Cisco's SDM allows user to configure a router from an HTTP or HTTPS interface

CCNA 4.5 View, Save & Erase Config

• To manually save the config file from DRAM to NVRAM, use copy running-config start-up config command
• To view config file, use show running-config (sh run) / startup-config (sh start) command
• To delete startup-config file, use erase startup-config command

CCNA 4.4 Router Interfaces

• Different Cisco routers have different interface methods
• Interface commands example:

interface e0 (2500)

interface fastethernet 0/0 (2600)

interface serial 0/1/0 (2800)

• No shutdown interface command enables an interface
• Users can check an interfaces' status via show interface or show running-config commands
• To configure IP addresses on an interface, use the ip address command from interface configuration mode
• | (output modifier) command allows user to goto specific ouput within the configurations
• To configure a serial interface, user can use clock rate command to set the clock rate of DCE connection (for DTE with no CSU/DSU)
• show controllers int command allows user to check whether a router has DCE cable connected to it
• Bandwidth command allows user to set data rate on serial link (for EIGRP, OSPF best path calculation)

CCNA 4.3 Cisco Router & Switch Admin Configs

• Config commands that helps user to admin the network are: hostname, banner, passwords & interface description (for network troubleshooting & maintenance)
• Hostname command allows user to set identity to the router
• Banner command allows user to show personal information/message on router
• Example of banner command includes: Exec, Incoming, Login & MOTD commands
• Five passwords are used to secure Cisco router: console, auxiliary, telnet (VTY), enable password & enable secret.
• Description command allows user to set descirption on a router interface
• do command allows user to view configurations and statistics from config mode

CCNA 4.2 Cisco Command Line Interface (CLI)

• CLI can be accessed by pressing "Enter" after router's boot up
• User mode allows user to view statistics data of the router
• Privileged mode allows user to view and change router parameter
• Configure terminal (config t) command allows user to be in global config mode and make changes to running-config (config running in DRAM)
• Configure memory (config mem) command allows user to make changes to startup-config (config stored in NVRAM)
• Configure network (config net) command allows user to make changes to router configuration stored on a TFTP host
• Config t, mem, net commands are all used to config info into RAM on router
• Interface command on global config mode allows user to make changes to an interface
• Subinterfaces allow user to create logical interfaces within the router
• Line command allows user to configure user-mode passwords
• Router term:

• ? command on any prompt allow user to obtain a list of commands on that prompt
• Router-command history:

• Show version command allows user to obtain basic configuration for system hardware, software version and boot image

CCNA 4.1 Cisco Internetwork Operating System (IOS) User Interface

• IOS is the kernel of Cisco routers & switches. (part of OS which allocates resources and manages low-level hardware interfaces and security)
• Cisco router IOS is responsible for network protocol functionality, traffic between devices, network security, network scalability and reliability.
• Access to the IOS command line is called an EXEC session
• Cisco router IOS can be accessed through console port, auxiliary port & telnet (in band)
• After Cisco router is turned on, it will run a Power On Self Test (POST). If pass, it will load the Cisco IOS from flash memory (EEPROM) and start-up config from RAM/NVRAM
• On non-ISR router, when there is no config file on NVRAM, the router will broadcast through TFTP host for a valid config file. If no file is found, the router will enter setup mode

CCNA 3.4 IP Addressing

CCNA 3.3 Summarizations

CCNA 3.2 Variable Length Subnet Masks (VLSMs)

• VLSM networking takes one network and create many networks using subnet masks of different lengths on different types of network designs
• Router in classful routing assumes all interfaces within the classful address space have the same subnet mask (RIP & IGRP)
• Router in classless routing supports the advertisement of subnet information (RIPv2, EIGRP, OSPF)

CCNA 3.1 Subnetting Basics

• Subnetting breaks one large network into several smaller networks
• IP subnet-zero is a command line that allows you to use the first and last subnet in network design
• Subnetworks are created by taking bits from the host portion of IP address and reserving them for subnet address
• Subnet mask is a 32 bit value that allows the recipient of IP packets to distinguish the network ID portion of the IP address from the host ID portion of the IP address
• Default subnet mask (starting):

• Classless Inter-Domain Routing (CIDR) is the method that ISPs use to allocate a number of addresses to a company/home/user
• Class A network address has CIDR value of /8 - /15
• Class A, B network address has CIDR value of /16 - /23
• Class A, B, C network address has CIDR value of /24 - /30
• 
  

CCNA 2.3 Broadcast Addresses

• Four type of broadcasts:

Layer 2 broadcast

Layer 3 broadcast (ARP)

Unicast (DHCP)

Multicast

• Example of L2 broadcast address: FF.FF.FF.FF.FF.FF
• Example of L3 broadcast address: 255.255.255.255
• Range of multicast addresses: 224.0.0.0 - 239.255.255.255

CCNA 2.2 IP Addressing

• An IP address consists of 32 bits of information (divide into four octets)
• The 32 bit IP address is a structured or hierarchical address
• Network address uniquely identifies each network
• Node/Host address uniquely identifies each device on a network
• Three classes of networks:

• In Class A network address the first bit of the first byte must always be off (0-127)
• In Class B network address the first bit of the first byte must always be on but the second bit is always off (128-191)
• In Class C network address the first two bit of the first byte must always be on (192-223)
• Class D network is used for multicast address (224-239)
• Class E network is used for scientific purpose (240-255)
• Reserved IP addresses:

• Private IP address is used for security measure and saving IP address space
• Reserved private IP address space:

CCNA 2.1 TCP/IP model and the DoD model

• DoD model composed of four layers:

Process/Application layer
Host-to-host layer
Internet layer
Network access layer

• Process/Application layer includes protocols such as Telnet, FTP, TFTP, NFS, SMTP, LPD, X Window, SNMP, DNS, DHCP/BootP
• Telnet, specializes in terminal emulation, allows user on a remote device to access the resource of another device
• File transfer protocol (FTP) allows user to transfer, rename files and list, relocate file directories between hosts
• TFTP (Trivial) is the lite version of FTP (no directory browsing and authentication functions)
• Network File System (NFS) allows two differents type of file systems to interoperate (file sharing etc)
• Simple Mail Transfer Protocol (SMTP) utilizes a spooled/queued method for sending mail
• Post Office Protocol (POP) is used for receiving mail
• Line Printer Daemon (LPD) allows print jobs to be spooled and sent to network's printer via TCP/IP (printer sharing)
• X windows allows a client PC to display on another remote PC
• Simple Network Management Protocol (SNMP) collects network information(baseline), alerts (traps) from network devices (agents) and monitor them through a management station.
• Domain Name Service (DNS) allows user to resolve a fully qualified domain name (FQDN) to an IP address
• Dynamic Host Configuration Protocol (DHCP)/Bootstrap (BootP) assigns IP addresses to hosts. (connectionless/UDP)
• Host-to-host layer includes protocols such as Transmission Control Protocol (TCP) and User Datagram Protocol (UDP)

• TCP segment format:

• UDP segment format:

• Port numbers are used by TCP & UDP to communicate with upper layers:

• Port numbers below 1024 are considered well-known (RFC-3232)
• DNS use both TCP and UDP:

• Internet Layer includes protocols such as Internet protocol (IP), Internet Control Message Protocol (ICMP), Address Resolution Protocol (ARP), Reverse Address Resolution Protocol (RARP) and Proxy ARP
• IP fragments segments from Host-to-host layer into packets. (RFC 791)
• IP Header

• Protocol/Type field in an IP header allows IP to communicate with protocols at Host-to-host layer

• Popular protocol numbers:

• ICMP is a management protocol and messaging service provider for IP
• ICMP is deployed on following events: destination unreachable, buffer full, hops limit, ping and traceroute
• ARP finds the hardware address of a host from a known IP address
• RARP is used by diskless device to discover its IP address by sending out a packet that includes its MAC address
• Proxy ARP allows devices on a subnet to reach remote subnets without configuring routing or default gateway

CCNA 1.7 Cisco Three Layer Hierarchical Model

• Cisco define three layers of logical hierarchy:

Core layer: backbone

Distribution layer: routing

Access layer: switching

• Core layer is responsible for transporting large amounts of traffic both reliably and quickly
• Distribution layer is responsible for routing, filtering and WAN access
• Access layer controls user and workgroup access to internetwork resources

CCNA 1.6 Data Encapsulation

• During data transmission, data is encapsulated with Protocol Data Units (PDUs) at each layer of the OSI model

• PDU and layer addressing

CCNA 1.5 Ethernet Cabling

• Three types of Ethernet Cable: Straight-through, Crossover & Rolled
• Straight-through cable is used to connect Host/Router to Switch/Hub

• Crossover cable is used to connect Hub-Hub, Switch-Switch, Host-Host, Hub-Switch, Router-Host

• Rolled cable is used to connect Host to router console serial com port

CCNA 1.4 Ethernet Networking

• Ethernet is a contention media method that allows all devices on a network to share the bandwidth of a link
• Ethernet utilizes Carrier Sense Multiple Access with Collision Detection (CSMA/CD) to avoid packets collisions
• When collision occurs, a jam signal is send to all device to stop transmission until the backoff timer expire
• Half-duplex Ethernet use one wire pair and share a collision domain
• Full-duplex Ethernet use two wire pairs and has own collision domain (no hub)
• Ethernet at Layer 2 is responsible for Hardware/MAC addressing
• Ethernet MAC address format:

I/G = Individual/Group (broadcast or multicast) bit = 0/1

G/L = Global/Local bit = 0/1

OUI = Assigned by IEEE to org

• Ethernet frame format:

Preamble = provides a 5 MHz clock at start of packet to lock incoming bit stream

DA = Destination Address

SA = Source Address

Type = Network Layer protocol identification

Data = Packet from Layer 3 to 2 (64-1500 bytes)

FCS = Frame Check Sequence (for CRC storing)

• IEEE 802.3 Standard:

10Base2 = 10Mbps, baseband, up to 185m (thinnet)

10Base5 = 10Mbps, baseband, up to 5oom (thicknet)

10BaseT = 10Mbps, category 3 UTP wiring

100BaseTX = 100Mbps, category 5, 6, 7 UTP two-pair wiring, 100m (802.3u)

100BaseFX = 100Mbps, 62.5/125 micron multimode fiber, 412m (802.3u)

1000BaseCX = 1Gbps, copper twisted-pair(twinax), 25 m (802.3z)

1000BaseT = 1Gbps, category 5 UTP four-pair wiring, 100m (802.3ab)

1000BaseSX = 1Gbps, 62.5/50 micron multimode fiber, 220m/550m (802.3z)

1000BaseLX = 1Gbps, 9 micron single mode fiber, 3-9km (802.3z)

CCNA 1.3 The OSI Reference Model

• OSI has seven layers, divide into two groups: Application, Presentation and Session layer; Transport, Network, Data Link and Physical Layer
• The top three layers define applications communication between end stations
• The bottom three layers define data transmission between end points
• Application Layer provides interface between actual application programs
• Presentation Layer presents data to Application layer and responsible for data encryption, compression and translation services
• Session Layer separates different applications' data from other applications' data, provides dialog control between nodes and organize systems communication through simplex, half duplex and full duplex mode.
• Transport Layer provides reliable (TCP) or unreliable (UDP) end-to-end delivery by reassembling data from upper layers into a data stream and performs error correction before retransmit
• Reliable networking (connection-oriented) at the Transport Layer can be achieved through flow control, sequencing and acknowledgment
• Flow control allows receiver to govern the amount of data sent by sender through buffering, windowing and congestion avoidance.
• Buffer acts a memory section of receiver to store data from sender
• Window is the quantity of data (bytes) that the sender is allowed to sent without acknowledgment from receiver
• Acknowledgment requires receiver to send ack to sender when it receives data
• Network Layer provides routing service within an internetwork with two types of packets: data (IP, IPv6) and route update (RIP, RIPv2) packet
• Data Link Layer provides access to device in a LAN through hardware address, format packets into frames and perform error detection
• Data Link Layer has two sublayers: Media Access Control (802.3) and Logical Link Control (802.2)
• MAC defines how packets are placed on the media
• LLC identifies network layer protocol and then encapsulates them
• Physical Layer activates, maintains and deactivates physical link between actual communication media through sending and receiving bits

CCNA 1.2 Internetworking Models

• Open System Interconnection (OSI) was created by International Organization for Standardization (ISO) to standardize internetworking
• OSI model utilizes layered architecture
• Changes in one OSI layer doesn't affect other layers

CCNA 1.1 Internetworking Basics

• Internetwork is created when two or more LANs or WANs are connected via a router
• Network Segmentation involves breaking up a network into a number of smaller portions for network traffic efficiency
• Network Segmentation can be achieved by using devices such as router, switches and bridges (Hub doesn't segment network)
• A switch/bridge can replace the hub, breaking up collision domains
• A router can replace the switch/bridge, breaking up broadcast domains

CCNA: Introduction

• Cisco is the king of internetworking world! =)