CCNA Cram Sheet - FileDen

By Janice King,2014-06-17 08:12
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CCNA Cram Sheet - FileDen ...


    Provides an interface between a host’s communication software and any necessary external applications

    Evaluates what resources are necessary and the available resources for communication between two devices

    Synchronises client/server applications

    Provides error control and data integrity between application

    Provides system independent processes to a host


    Presents data to the Application layer

    Acts as a data format translator

    Handles the structuring of data and negotiating data transfer syntax to Layer 7 Processes involved include data encryption, decryption compression and decompression


    Handles dialog control among devices

    Determines the beginning middle and end of a session or conversation that occurs between applications (intermediary)


    Manages end to end connections and data delivery between two hosts

    Segments and reassembles data

    Provides transparent data transfer by hiding details of the transmissions from the upper layers


    Determines best path for delivery across the network

    Determines logical addressing, which can identify the destination of a packet or datagram Uses data packets (IP, IPX) and route update packets (RIP, EIGRP, and so on) Uses routed protocols IP, IPX, and AppleTalk DDP

    Devices include routers and Layer 3 switches

Data Link

    Ensures reliable data transfer from the Network layer to the Physical layer Overseas physical or hardware addressing

    Formats packets into a frame

    Provides error notification

    Devices include bridges and Layer 2 switches


    Moves bits between nodes

    Assists with the activation, maintenance, and deactivation of physical connectivity between devices Devices include hubs and repeaters

Exam Cram

    The CCNA Cram Sheet

    This Cram Sheet contains key facts about the CCNA exam. Review this information as the last thing you do before you enter the

    testing center, paying special attention to those areas in which you feel that you need the most review. You can transfer any of

    these facts from your head onto a blank sheet of paper immediately before you begin the exam.

OSI Model

    Layer Name Protocols and Devices PDU

    7 Application FTP, Telnet, TFTP, SMTP, POP3, SNMP, DNS, NTR, HTTP, HTTPS, DHCP Data

    6 Presentation ASCII, .jpg, .doc Data 5 Session RPC, SQL/Telnet (for login only) Data 4 Transport TCP Connection-oriented, reliable using PAR Segment

    UDP Connectionless, unreliable, uses upper layer protocols for reliability

    3 Network IP, ICMP, RIP, IGRP, EIGRP, OSPF Packet

    Routing and Path determination, logical addressing

    2 Data Link Ethernet, Frame Relay, PPP, HDLC Frame

    Physical (hardware) addressing (MAC addresses)

    1 Physical Bits transmitted on media Bits

    Hubs, Repeaters, Connectors

TCP and UDP Ports

    TCP Ports UDP Ports

    FTP 20, 21 DNS 53

    Telnet 23 DHCP 67, 68

    SMTP 25 TFTP 69

    DNS 53 NTP 123

    HTTP 80 SNMP 161

    POP 110

    NNTP 119

    HTTPS 443

    TCP utilises Positive Acknowledgement and Retransmission (PAR):

    ; The source device starts the timer fro each segmentl retransmits if acknowledgment is not recieved before the timer


    ; The source device records all segments sent and expects and acknowledgment of each.

    ; The destination device acknowledges receipt of a segment by sending an ask for the next dequence number it expects.

Be able to recognise a TCP header Be able to recognise a UDP header

     Source Port Destination Port Source Port Destination Port

    Sequence Number Length Checksum

    Acknowledgment Number

    Misc. Flags Window Size

    Checksum Urgent



    ; Proprietary (Cisco only) Data Link (Layer 2) protocol

    ; L3 protocol and media independent

    ; Uses L2 multicast to gather hardware and protocol information about directly connected devices.

    ; Enabled by default; can be disabled globally by no cdp run.

    ; To learn remote device L3 addresses, hardware platform and IOS ver, use

    Show cdp neighbor detail


    show cdp entry *

Lan Technology

    ; Ethernet physical addressing = MAC addresses.

    o 12 hexadecimal digits

    o First six digits are OUI of NIC manufacturer

    ; PC to switch/hub = straight-through cable

    ; Hub-hub, switch-switch, PC-PC, router-router, PC-router directly (no switch/hub): use cross-over cable

    ; Switches, bridges, and routers segment a network. Hubs and repeaters EXTEND a network.

; Switches increase the number of collision domains, do not segment broadcase domains. Routers, L3 switches, and VLANs

    segment broadcast domains.


    ; A switch is a multiport bridge. Switches forward frames using hardware ASIC, making them faster than bridges. Dedicated

    bandwidth per port.

    ; Bridges and switches learn MACs by reading the source MAC of each frame. ; Switches operate in one of three modes:

    o Store-and-ForwardL Entire frame is buffered. FCS is run (error checking).

    o Cut-throughL Only destination MAC is read, frame is forwarded.

    o Fragment-Free: First 64 bytes of frame are buffered, frame is forwarded,. Cisco proprietary. ; Half-duplex: Shared collision domain and lower throughtput

    ; Full-duplex: Point-to-point and higher throughput

    ; To remotely manage a switch, you need an IP address, subnet mask, and default gateway. The switch must be reachable on

    a port in its maangement VLAN.


    ; Logically divide a switch into multiple, independent switches at L2 ; Create separate broadcast domains in a switch, increasing the number of broadcast domains ; Span multiple switches using trunks

    ; Allow logical grouping of users by function

    ; Simplify adding, moving, and changing hosts in the network

    ; Enhance security

    VLAN configuration steps:

    1. The VLAN must be created.

    2. The VLAN may be named.

    3. The desired ports must be added to the new VLAN.

    4. Routing between VLANs requires a router or a Layer 3 switch.


    Trunks carry traffic from multiple VLANs over a single connection (cross-over cable). The VLAN ID is tagged using one of two


    1. ISL

    2. IEEE 802.1q

    ; A trunk can operate in one of five modes:

    o Dynamic Auto

    o Dynamic Desirable

    o On

    o Off

    o Nonegotiate

VTP (VLAN Trunking Protocol)

    VTP simplifies VLAN administration. Configuration of VLANs is distributed to all switches in a VTP domain from a single server-mode


    The three VTP modes are as follows:

    ; Server

    ; Client

    ; Transparent

    ; Switches must be in the same VTP domain, and must use the same password to exchange VTP information.

Spanning Tree Protocol (STP IEEE 802.1d)

    ; L2 protocol prevents switching loops in networks with redundant switched paths.

    ; Root switch is the one with lowest STP Priority: if tied, low MAC is the Root

    ; Root Port has the least-cost path to the Root switch

    ; STP path cost is determined by the sum of the costs based on bandiwidth.

    ; Spanning Tree Topology Ports states:

    1. Blocking: Sending no data, listening for BPDUs

    2. Listening: Sending and recieving BPDUs

    3. Forwarding: Normal operation

    ; Convergence: 50 seconds (20 sec Max Age + 15 sec Fwd Delay + 15 sec Fwd Delay)

Boot Sequence For Router/Switch

    1. POST Device finds hardware and performs hardware-checking routines.

    2. Locate IOS.

    3. Load IOS.

    4. Locate configuration (startup-config).

    5. Load configuration (running-config).

    Configuration register settings:

    ; 0x2102 (default): Checks NVRAM for “boot system” commands; if none, loads first valid IOS in Flash.

    ; 0x2100: Boots into ROM Monitor mode (ROMMON).

    ; 0x2101: Boots into ROM RxBoot mode. RxBoot can connect to a TFTP server to download an IOS to Flash.

    ; 0x2102: Ignores startup-configuration in NVRAM when booting (for password recovery). Memory Components of a router/switch:

    ; ROM: Basic microcode for starting and maintaining device Power On Self Test (POST), bootstrap, ROM Monitor (ROMMON),


    ; Flash memory: Stores IOS

    ; NVRAM: Stores startp-config (configuration loaded at bootup)

    ; RAM: Running IOS and running-config (active configuration after startup)

Securing Your Router

    ; To configure a password on all five telnet lines, the configuration will be similar to the following:

    Router(config)# line vty 0 4

    Router(config-line)# password cisco

    Router(config-line)# login


    Default Administrative Distances:

    Connected Interface 0

    Static Route 1

    EIGRP Internal 90

    IGRP 100

    OSPF 110

    RIP 120

    EIGRP External 170

Static Route

    Router(config)#ip route The default route syntax is

    Router(config)#ip route

    Distance Vector Routing Protocols

    ; Advertise the entire routing table to directly connected neighbours, and send the updates regardles of whether a change

    has occurred (every x seconds). RIPv1, RIPv2, IGRP.

    Link State Routing Protocols

    ; Sends updates containing the state of their own links to all other routers on the network.

    Examples are OSPF, ISIS.

    ; Triggers exchange of advertisement by a change in the network.

    ; Builds and maintains topological database from hello packets and LSAs (Link State Advertisements) from other routers.

    ; Calculates the paths to each destination from the topological database and places the best of them into the routing table

    Classful (FLSM) Versus Classless (VLSM)

    ; Classful (RIPv1, IGRP, EIGRP by default): Does not advertise subnet masks.

    ; Classless (RIPv2, IS-IS, OSPF, EIGRP): Advertises subnet mask Route Summarisation

    Route summarisation/aggregation/supernetting represents several networks/subnets as one large network address, by shortening

    the subnet mask to include only the “in-common” bits from all the networks.


    Syntax: directly conneced, classful networks:

    Router(config)#router rip




    ; IGRP’s compose metric = Bandwidth, Delay by default; Reliability, Load, and MTU optional.

    ; IGRP max hop count = 255.


    ; EIGRP: fast convergence, VLSM support. Multiprotocol support: IP, IPX, AppleTalk. EIGRP maintains routing, topology, and

    neighbour tables for each protocol.

    ; EIGRP metric same as IGRP, but 32-bit versus IGRP 24-bit metric.

    ; The successor route is the best route, loaded in the route table. Feasible successor is the backup route in the Topology table.

    ; EIGRP max hop count = 224


    ; Scalable (unlimited hop count), vendor-neutral, link-state, VLSM support. OSPF areas:

    ; Areas may be assigned any number from 0 to 65535.

    ; Area 0 is the backbone area.

    OSPF RouterID criteria:

    ; Highest IP address on a loopback (logical) interface.

    ; If no loopback, then highest IP address on physical interface. DR/DBR elections only in the following topologies:

    1. Broadcast multi-access (for example, Ethernet)

    2. Non-broadcast multi-access (for example, Frame-Relay)

    To configure OSPF for network in area 0

    Router(config)#router ospf 7

    Router(config-router)#network area 0 8The OSPF Metric = cost. Cost = 10/bandwidth in bps.

Access Lists

    ; Implicit deny any at end: Every access list must have at least one permit, or it denies all traffic.

    ; Standard IP access lists filter the entire IP protocol based on the source IP address/network.

    Number range 1-99. Places as close to destination as possible.

    ; Extended IP access lists filter based on the source IP address/network, destination IP address/network, specific protocols

    (TCP, UDP, ICMP...) and port number. Places as close to source as possible.

    ; One access list per direction per protocol per interface.

    ; Wildcard mask: 0s match; 1s ignore corresponding bit in address Extended access-list syntax:

    access-list [list#] [permit | deny] [protocol] [source ip] [WCmask] [dest. Ip] [WCmask] [operator] [operand]


    The common WAN serial encapsulations are

    ; HDLC

    ; PPP

    ; Frame Relay

    ; Encapsulation type must match on both ends of a link

Network Address Translation

    ; NAT maps private IP addresses to public registered addresses.

    ; Static: ip nat inside source static [inside ip] [outside ip]


    ; Inside local: A private IP address assigned to a host on the inside network

    ; Inside global: A registered Internet address that represents an inside host to an outside network

    ; Outside global: The registered address of an Internet host

    ; Outside local: The address of the Internet host as it appears on the inside network Sample PAT configuration, using a pool of addresses to translate to (named MyPool, starting with and ending with

    access-list 1 permit

    ip nat pool MyPool netmask ip nat inside source list 1 pool MyPool overload

    interface Ethernet 0

    ip nat inside

    interface serial 0

    ip nat outside


    Vendor-neutral: Cisco to Non-Cisco

    Can encapsulate multiple L3 protocols on single L2 link

Configuration of PPP

    RtrA(config)#username RtrB password same pass

    RtrA(config)#interface bri 0

    RtrA(config-if)#encapsulation ppp

    RtrA(config-if)#ppp authentication chap

RtrB(config)#username RtrA password samepass

    RtrB(config)#interface bri 0

    RtrB(config-if)#encapsulation ppp

    RtrB(config-if)#ppp authentication chap


    ; Two data link layer encapsulation, one for data and one for signaling:

    o D channel (16/64 kbps) LAPD (0.921) for out-of-band signaling

    o B channel (64kbps each) PPP (common), HDLC, SLIP for data

    ISDN Reference Points and Interfaces:

    ; TE1 = native ISDN device

    ; TE2 = non-ISDN device

    ; R interface (similar to a serial interface) is for TE2 to TA

    ; S/T interface: 4 wire

    ; U interface: 2 wire, connects to Telco (North America/Japan).

Frame Relay

    ; DLCIs identify the circuit (PVC) between the router and the frame switch, DLCI is the L2 address in frame relay.

    ; LMI is signalling between the router and the local frame relay switch. LMI types are as follows:

    o Cisco (the DEFAULT)

    o ANSI

    o 0.933a

    ; Two Frame Relay encapsulations (must match on both routers):

    1. Cisco (default)

    2. IETF

    ; Point-to-point subinterfaces solve Spilt Horizon issues, and map a single subnet to a single DLCI.

    ; Removes IP address on physical interface if using subinterfaces.

    ; Must specify sub-if as point-to-point or multipoint no default since IOS 12.0.

    ; In order to map Layer 3 IP addresses to Layer 2 DLCIs, Frame Relay uses inverse ARP, or static map:

    (config-if)#frame-relay map ip [next-hop-address] [local DLCI] broadcast

    ; Broadcast keyword allows routing updates over the PVC.

Troubleshooting Commands And Outputs

    show interface serial 0

    ; Serial 0 is Up/Line protocol is up: Interface is working.

    ; Serial 0 is Up/Line protocol is down: Layer 1 is up. Layer 2 is down (clocking or mismatching frame types).

    ; Serial 0 is Down/Line protocol is down: Layer 1 down. (Fault or remote end is shut down.)

    ; Administratively down/Line protocol is down: Interface is shut down and must be no shut.

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