CCNA IMPORTANT TOPICS (Interview Related)

1.     Ø  Core layer: Considered as the backbone of the network (high-end switches, high-speed cables). Concerned only with speed and reliable delivery of data. No packet filtering happens here.

Ø  Distribution layer (Workgroup layer): Ensures packets are properly routed between subnets and VLANs using LAN-based routers and Layer 3 switches.

Ø  Access layer (Desktop layer): Deals with connecting workstations to the network with switches and hubs

Ø  A trunk link is a point-to-point link between two switches, a switch and router or a switch and server which carries multiple VLAN traffic

Ø  Bridges are software based and can only have one spanning-tree instance per bridge, while switches are hardware based and can have many.

Ø  The original Spanning-Tree protocol was created by Digital Equipment Corporation (DEC) which is now part of Compaq. The IEEE created its own version called IEEE 802.1d which is not compatible with the original version.

Ø  To change the router configuration stored on TFTP you configure network (config net)

Ø  To find out which interface associated with a given MAC address

Ø  -show mac-address-table command

Ø  To determine the trunking status of a link and VLAN status/which trunk ports will receive a frame

Ø  -show interface trunk

Ø  To determine the what type of device neighbor is

Ø  -show cdp neighbors

Ø  To check the switch that is root bridge for VLAN1

Ø  -show spanning-tree vlan 1

Ø  To identify which vlan a particular interface belongs to

Ø  -show vlan

Ø  To know the vtp configuration information

Ø  -show vtp status

Ø  To find out the ip address of a neighbor

Ø  -show cdp neighbor detail

Ø  To check the vlan information of particular switch

Ø  -show vlan

Ø  To find out the defualt gateway of the switch

Ø  -show running-config

Ø  portfast is a method of disabling STP on a switch port.

Ø  STP switch port states: Blocking, listening , leraning , forwarding , disabled

Ø  RSTP is interoperable with legacy STP, but some features are lost when some switches are running
STP. e.g. Fast convergence.

Ø  Flow Control and Congestive Feedback are functions of the Network layer. Bridges operate

Ø  at the data Link layer so these responsibilities fall to the end devices in a bridged environment.

Ø  Fragment Free is also referred to as Modified Cut-Through. It is the default mode used by Cisco Catalyst 1900 series switches. This switching method is the same as with Cut-Through except the switch will check the first 64 bytes of every frame received as this is where the vast majority of errors occur within a frame.

Ø  To erase the startup configuration use the following command:
Router#erase startup-config or Router#erase startup

Ø  The various states of an interface:

Ø  Ethernet0 is up, line protocol is up - The interface is functioning correctly.

Ethernet0 is down, line protocol is down - This message usually represents a physical interface problem. The cable may be disconnected. This can also occur if this interface is connected to another router whose interface has been shut down.

Ethernet0 is up, line protocol is down - The Physical layer connectivity is not the issue. The line protocol being down is either a clocking issue (keepalives) or a mismatch of the frame types being used on connected devices.

Ethernet0 is administratively down, line protocol is down - The interface has been manually shutdown using the shutdown command.

Ø  To turn off CDP use the no cdp run command from the global configuration mode.

Ø  IGRP sends its routing table to its neighbors every 90 seconds. IGRP uses an invalid timer to mark a route as invalid after 270 seconds (three times the update timer). IGRP uses a flush timer to remove a route from the routing table (default flush timer is 630 seconds, seven times the update period).

Ø  A switched network can be described as a flat network because broadcasts are transmitted to every device.

Ø  Cisco's proprietary VLAN tagging (ISL) has a maximum frame size of 1548 bytes.
 IEEE 802.1q VLAN tagging has a maximum frame size of 1522 bytes.

Ø  If you wish to remove an access-list, you use the no access-list (list #) command

Ø  HDLC and PPP are WAN encapsulations that are typically used on a leased line
802.11a operates in the 5GHz band with a data rate of up to 54Mbps and is immune to interference from other devices operating in the 2.4GHz spectrum.

Ø  Cisco routers are DTEs by default (Data Terminal Equipment). The DCE (Data Circuit-Terminating Equipment) at the other end of the connection must supply a clock rate to the DTE. Interface needs clock rate when it is DCE.

Ø  IP provides no form of error correction/acknowledgements.

Ø  Cisco enhanced the original 802.1d specification with features such as Uplink Fast, Backbone Fast, and Port Fast to speed up the convergence time of a bridged network. However these new features are proprietary, and can only be configured on Cisco switches.

Ø  In Transparent mode switch just forwards update sent by other switches without reading it. It doesn’t update its VLAN database so the Configuration Revision doesn’t increase.

Ø  Dynamic Trunking Protocol (DTP) is a Cisco proprietary protocol for negotiating trunking on a link between two devices and for negotiating the type of trunking encapsulation (802.1Q) to be used.

Ø  You can have more than one static route in your  routing table.

Ø  Two ways to discover neighbors on an NBMA network: static neighbor, point-to-multipoint

Ø  Switches does not use a shared medium as opposed to hubs. Computers connected to a switch port can transmit data simultaneously without having the need to wait for other PC’s to complete data transmission

Ø  1. To to see how many management packets have been sent to the frame relay switch?
    - show frame relay lmi

2. To find out if your static NAT is working or not?
     - show ip nat translations.

3. Which command will generate a level 7 password in router?
    - enable password

4. If you want to ping router R2 continuously on your network with IP

Ø  address 172.16.3.1. Which command will you use to ping a name.
    - R1(config)# ip host R2 172.16.3.1

5. You need to leave the room for few minutes and want to secure the console

Ø  session on your laptop with one time password . Which two commands will

Ø  u need to apply?
    - lock and lockable

6. You are configuring an EIGRP hub router and you need it to advertise a network

Ø  out of the same interface it learned it on . What command will accomplish it ?
    - R (config-if)# no ip split-horizon eigrp 100

7. Which command will enable a secure version of CHAP to be sent from your router

Ø  to a neighbor router?
    - R1(config-if)# ppp authentication chap

8. You want your router interface to forward DHCP requests to a specific router on

Ø  the network. What command will achieve this?
    -R(config-if)# ip helper-address 10.1.1.1

9. opsf hello interval can be changed and it should be in sec
    Router(config-if)#ip ospf hello-interval ?
    <1-65535>  Seconds

10. ­­Dead interval will change automatically once there is change in hello

11. We need to change hello interval on both routers which are going to form

Ø  neighbor otherwise adjacency won't happen.

12. On point to point network we need to configure frame-relay interface-dlci 321

Ø  instead of frame-relay map command. Frame-relay map command is used in

Ø  point to multipoint n/w

13. For hub and spoke topology we need to configure neighbor in hub and set

Ø  the priority to 0 in spokes to restrict them to take part in ospf DR/BDR process.

14. attempt will only seen in NBMA

15. Timer default for point to point are 10 sec and 40 sec but for etherent and

Ø  non broadcast NBMA hello is 30 and dead is 120 secs.

16. The channel provided by ISDN BRI is
      -2B+ 1D

17. Running both Ipv4 and ipv6 on a router simultaneously is known as

Ø  dual-stack tunneling.

18. Three Ipv6 transition mechanism?
      -6t04 tunneling
      -ISATAP tunneling
      -teredo tunneling

19. antispyware: detects software designed to capture sensitive information                                                                   

Ø  and removes it from the computer

20. firewall: filters traffic based on source and destination IP address or traffic type

21. Five steps of boot sequence
     The power-on self test executes
     The bootstrap loader in ROM executes
     The IOS is loaded based on boot system command in NVRAM
     The router looks for the configuration in NVRAM
     If no configuration file is located, the setup dialog initiates.

22. Rollover: PC serial port to switch console port

23. Advantages of RIP over ospf
     -is less complex to configure
     -demands fewer router resources

24. What are the characteristics of 802.1Q protocol?
      -it modifies the 802.3 frame header, and thus requires that the FCS be recomputed.
      -it is a trunking protocol capable of carrying untagged frames.

25. Which PPP sub protocol negotiates authentication options?
       LCP

26. Which two statements apply to dynamic access lists?
       -you can set a time based security policy.
       -they are used to authenticate individual users.

Ø 
27. Which command helps a network administrator to manage memory by

Ø  displaying flash memory and NVRAM utilization?
     -show file systems

28. Which ieee standard protocol is initiated as a result of successful DTP completion

Ø  in a switch over fastethernet?
      -802.1Q

29. Which Ipsec security protocol should be sued when confidentiality is required?
      -ESP

30. Maximum no of equal cost paths that can be placed into the routing of a cisco

Ø  ospf router?
      4

31. ip default-gateway command only used for the devices which does not support

Ø  ip routing ie switches. In cisco IOS routers ip routing is enabled by default .to use

Ø  ip default-gateway in cisco routers we need to disable ip routing.

      The major difference between these two options is that configuring a static
      default route only defines a default route for the router you're configuring it on,

Ø  while ip default-network will propagate the route via its routing protocol.

32. Three features of IPv6 protocol
      -plug and play
      -no broadcast
      -auto configuration

33. Which command shows you active telnet connections?
       show sessions

34. Which command alllows you to verify encapsulation type(cisco or ietf) for a

Ø  frame realy link?
      -show frame-relay map

35. Which device might be installed at a branch office to enable and manage an

Ø  IPsec site-to-site VPN?
      -cisco adaptive security appliance


36. sh interface will give line , protocol, dlci and lmi info

Ø  sh cdp interface will give cdp enabled interface on your router.

Ø  no frames are transmitted or received on blocked ports

Ø  bpdu's are still received on blocked ports.

Ø  bpdu's are used to send conf messages using multicasts frames.

Ø  sh hosts --will show the host name resolved to an ip address

Ø  on the router.

Ø  inbound access lists--incoming packets are processed before being

Ø  routed to an outbound interface. No router lookup.

Ø  outbound access lists--incoming packets are routed to the outbound

Ø  interface and then processed.

Ø  isl operates in a point-to-point environment, operates at layer 2,

Ø  header contains 15 bit vlan id.

Ø  vtp info are sent over vlan 1

Ø  catalyst 1900 can have 64 vlans with a separate spanning tree

Ø  per vlan.

Ø  factory default vlans--1,1002,1003,1004,1005

Ø  sh span tree vlan number---spanning tree information for a vlan.

Ø  Ethernet lacks a mechanism to recognize and eliminate

Ø  endlessly looping packets.

Ø  stp-on a root bridge each port is a designated port.

Ø  bridge id=bridge priority + mac address.

Ø  tcp header is 20 bytes , udp has 8 bytes header

Ø  dns uses udp for name resolution, and tcp for server zone transfers.

Ø  networks 10.0.0.0,172.16.0.0 thru 172.31.0.0 , 192.168.0.0 are

Ø  reserved address and not used in public network.

Ø  term ip netmask-format {bitcount|decimal|hex}

Ø  display format for netmask for the current session.

Ø  config-line)#ip netmask-format {bit|decimal|hex}

Ø  cdp run is not available on 1900 switches.

Ø  snmp operate at application layer.

Ø  sh ip protocol----all routing protocols on the router.

Ø  Socket is made up of--layer 4 protocol, port number ,ip address.

Ø  cdp will provide info abt--identifier, platform and address.

Ø  bridge priority and bridge id ---are the factors that determine the

Ø  election of a STP root bridge.

Ø  vtp info are flooded thru a vtp domain every --5 minutes.

Ø  each port on catalyst 1900 cannot have unique ip address for

Ø  in band management.

Ø  cdp packets are sent to neighboring device every 60 secs by default.

Ø  split horizon with poison reverse. ---the routing protocol advertises

Ø  all routes out an interface, but those learned from earlier updates

Ø  coming in that interface are marked with infinity..

Ø  access list are default to outbound.

Ø  an eigrp metric is represented 256 times an igrp metric.

Ø  rip , igrp and eigrp can utilize 4 equal costs links.

Ø  NETBIOS operates at layer 5 session.

Ø  CIDR allows internet service providers to reduce the number of routes

Ø  carried in their routing tables.

Ø  sh config--startup config.

Ø  frame-relay map statement , frame-relay interface-dlci statements,

Ø  inv arp is used by a router to assign layer 3 addresses to layer 2.

Ø  auto summary cannot be disabled by rip version 1 and igrp.

Ø  ip subnet-zero----is used to enable the use of zero subnet.

Ø  vtp supports password authentication.

Ø  protocol tunneling----to transport multiprotocol over single protocol

Ø  backbone ,overcome discontiguous network problems, to allow virtual

Ø  private networks.

Ø  ip summary-address eigrp 100 ip mask  ---will summarize the network

Ø  for the the AS 100

Ø  max distance of 10basetx=100 mtrs

Ø  sh terminal ---will give u the history size on the router.

Ø  to resolve a name todd --ip host todd ipaddress

Ø  77. sh running will show the interfaces where access lists are assigned.

Ø  sh ip int , sh ipx int --will do the same.

Ø  78. tftp-server system image name---is used to configure a router so

Ø  It can become a tftp server host for a router system image that is

Ø  run in flash.

Ø  80 .max distance of fast Ethernet=100 mtrs.

Ø  when an Ethernet link is powered on --link speed and link duplex

Ø  are provided by the auto negotiation mechanism.

Ø  cisco router Ethernet int can use MAC address other than the burned

Ø  in address.

Ø  set vlan 100 4/1-24 ----will assign ports 1-24 on module 4 to vlan 100

Ø  84.

·         dns uses both tcp and udp.

·         each vlan will have its own root bridge.

·         atm and faddy are capable of vlan tagging.

·         atm is connection oriented.

·         sh process ---displays routers process

·         ios version 11.2 --lmi was first auto sensed.

·         auto summary is enabled by default for rip v 2 and igrp.

Ø  85. Named type of access list allows more than 99 standard and 100

Ø  extended access list to be created.

Ø  86.

·         cdp is not a subset of snap protocol.

·         cdp operates at data link layer.

·         no cdp run---disables cdp for all the interfaces on a router

·         auto summary cannot be disabled by rip v 1 and igrp.

·         write erase -on a router is same as delete nvram on 1900

·         subnet mask borrows bits from host field and designate them to subnet field.

·         Vlan membership --static and dynamic

·         VMPS-vlan  management policy server -creating MAC host table

·         vlan has two types of links-- access and trunk

·         access link--one vlan ,unaware of vlan membership

Ø  87.

·         network 10.11.12.13 ---will advertise the network on a router with

Ø  rip , igrp and eigrp enabled.

·         ppp multilink --will enable ppp multilink on a cisco bri interface.

·         sh span tree 100 ---will display the MAC address of the root bridge for vlan 100

·         two named access lists with the same name can be used on diff routers

Ø  in the same autonomous systems.

·         no debug all , and , undebug all ---cancel all debugging on a router.

·         ppp has a architected type field to determine the type of encap and

Ø  also performs error correction if chosen.

·         show compress ---shows the compression ratio.

·         frame relay is multiaccess--more than two device can attach to a medium.

·         there is a single dlci in a header--no source and destination dlci.

·         in frame relay split horizon is enabled for point to point interface.

·         ip split horizon interface ---can be used to change the default value.

·         OUI is the unique number assigned by IEEE for NIC manufacturers.

Ø  88.

·         snmp-server enable traps---allows syslog messages to be sent as

Ø  snmp traps.

·         to remove an access list 101(out bound) from a router

Ø  ---no ip access-group 101 out

·         net bios operate at session layer.

·         cisco routers cannot read and write files from flash memory to ftp

·         server.

·         ospf and eigrp support variable length subnet masks.

·         sh cdp nei det- will give the IOS version of the neig device

·         sh cdp traffic- gives the interface traffic

·         sh cdp interface -shows also the encapsulation of the line,timer

Ø  and holdtime

·         Dynamic trunk protocol (DTP) is used to send trunk info across

Ø  802.1q links. Its a PPP protocol.

·         vtp pruning is used to avoid broadcasts and multicasts from getting

Ø  into trunk links that need not need the info.

·         vlan 1 can never be pruned as it is the administrative vlan.

·         all switches are vtp server by default

Ø  89.

·         ip route 0.0.0.0 0.0.0.0 ipaddress -is the cmd for conf default route

·         adm distances C=0 , S=1 , RIP=120 ,IGRP=100 , EIGRP=90 , OSPF=110

·         RIP version 1 is classful routing.

·         IGRP is cisco prop , max hop count of 255 , default of 100,uses

·         band width and delay of line as default.

·         RIP timers 30-90-240  IGRP 90-270-280-630

·         AS number can be from 1-65535

·         igrp uses classful routing , no subnet mask sent

·         sh ip protocols -gives the routing protocols configured , along

Ø  with the timer values, s

·         debug igrp [events|transactions]--

Ø  events-igrp routing info running on the network

·         u cannot telnet from a 1900 switch if configured.

·         sh ip --will give the default ip configuration of the switch.

·         100basetx default is auto , 10baset default half duplex.

·         default conf for 1900--cdp enabled , def gateway 0.0.0.0

·         port secure mac-max-count 1 - for only one mac address for a port.

·         sh port system --shows the default switch mode. (fragment free)

Ø  90.

·         switching mode option---will change the default switching mode

·         vlan number name vlanname ---to configure vlan

·         vlan-membership static|dynamic vlannumber--assigning ports to vlan

·         sh vlan , sh vlan-membership ---will give ports assigned to vlans

Ø  (config-if)#no trunk vlan number --clearing the trunk vlan.

·         58.sh trunk trunknumber [options] --to see what vlans are allowed on

Ø  trunk ports.

·         (config-subif)# encapsulation isl vlannumber,ip address ---for changing the

Ø  encapsulation type.

·         sh vtp--- for verifying the vtp information.

·         if vtp pruning is set on server its set on the whole  domain.

·         spanning tree protocol is transparent to end stations.

·         in default settings the switch with the lowest MAC add is the root.

·         priority of switch is a  parameter to decide root switch.

·         STP states .blocking , listening,learning,forwarding, disabled.

·         ports stabalize to either forwarding or blocking state.

·         blocking state does not forward a frame.

Ø  91.

·         sh ipx servers ---shows the content of sap table in the router.

·         sh ipx route---shows the ipx routing table the router knows

·         ipx max-path number(till 64)--load balancing on routers.

·         sh ipx traffic--shows the rip and sap packets transmitted and recd

Ø  by the router.

·         sh ipx int intno.----gives the ipx status of that interface along with

Ø  the ipx addresses.

·         debug ipx routing [activity|events]--rip routing activity and events.

·         debug ipx sap activity---sap activity on ur router.

·         two PDU's at network layer---data and route

·         cut thru and fragment free have fixed latency time

·         it takes 50 secs for a switch port to go from blocking to forwarding.

Ø  92.

·         .up arrow key gives the previously entered cmd.

·         clear mac-address-table dynamic

·         to see transmit and recv statistics of vtp on 1900--sh vtp stat.

·         IEEE standard for stp 802.1d

·         udp works at host-to-host layer of DOD model

·         wins translates the netbios names

·         cdp is enabled by default , updates 60 secs , hold time 180 secs.

·         after a router boots by auto install , it first resolves its hostnames

Ø  it then looks for hostname-config to get specific configuration.

·         sh int---will only give the hardware address of an interface.

·         sh int --will give dlci and line speed for a frame relay.

·         cdp timer--will change the freq of cdp broadcasts

·         u can see router running conf in privileged mode.

·         local loop--link between demarc and the CO

·         igrp advertises three types of route..interior, exterior and system

·         sh ip protocol--will give the routing protocols on a router

·         for full duplex --loop back and collision detection are disabled.

·         ip host ipaddress name --to create host table         

·         sh protocols --will show the routed protocols.

·         to delete the configuration stored in nvram--erase startup.

·         lan switch mode that keeps crc to minimum but has a fixed latency

·         rate---fragment free.

Ø  93.

Ø  Command to set the clock
       #clock set 10:45:00 1 June 2011

Ø 
       To verify the new clock setting type.
       # show clock

Ø 
       Type terminal history size 5  to set the command history size to 5.

Ø 
       Type show terminal to see the terminal history size.

Ø 
       Type show history to view your last five commands

       Type terminal no history to disable the command history but Confusingly, 

Ø  no terminal history size resets this to the default, which is 10 commands.

       Type show flash to verify the amount of free flash memory you have.

       Type copy flash tftp to backup your IOS image to a TFTP server.

       Type show cdp to see the global CDP information.

       Type show cdp neighbors  to view connected devices.
       Note what information is displayed.
       Hostname, local interface, capability, platform, neighbor's device port Id

       If you want to find out more information on each directly connected device type 

Ø  sh cdp neighbors detail

94. To display just IP addresses of each directly connected device type show 

Ø  cdp entry * protocols

95. To display the IOS versions of each directly connected device type 

Ø  show cdp entry * version

96. Note: show cdp neighbors detail has the same output as show cdp entry *

97. Blocking        No frames forwarded, BPDUs heard
      Listening       No frames forwarded, listening for frames
      Learning        No frames forwarded, learning addresses
      Disabled        No frames forwarded, no BPDUs heard

98. 802.11b   ==     2.4GHz, 11Mbps

Ø  802.11a  ==      5GHz, 54Mbps

Ø  802.11g   ==     2.4Ghz, 54Mbps
      ROM monitor  == Used for testing and troubleshooting
     

Ø  Protocol used to update switches about new or old VLANs

Ø  VLAN Trunk Protocol (VTP)


99. Used to identify which frame belongs to which VLAN == Frame tagging
      802.11n  ==      2.4GHz or 5GHz, 300Mbps
      WEP == Original IEEE wireless security standard. Easily hacked.

Ø 
      WPA Wireless security standard created by the Wi-Fi Alliance. Uses a dynamic

Ø  key for greatly improved security over WEP. Interoperable with different

Ø  vendors products.

      WPA-2 Ratified by the IEEE in 2005 who named it IEEE 802.11i. Uses

Ø  AES encryption.

100. Serial encapsulation to use to connect to a non-Cisco router PPP for serial links
        Command to display hosts table == show hosts.