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