CCNA 200-125 Tips 1: Points to Remember

1.     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.

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

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

4.     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

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

6.     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.

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

8.     To find out which interface associated with a given MAC address

-show mac-address-table command

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

-show interface trunk

10.   To determine the what type of device neighbor is

       -show cdp neighbors

11.   To check the switch that is root bridge for VLAN1

-show spanning-tree vlan 1

12.   To identify which vlan a particular interface belongs to

-show vlan

13.   To know the vtp configuration information

-show vtp status

14.   To find out the ip address of a neighbor

-show cdp neighbor detail

15.   To check the vlan information of particular switch

-show vlan

16.   To find out the defualt gateway of the switch

-show running-config

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

18.   STP switch port states: Blocking, listening , leraning , forwarding , disabled

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

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

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

21.   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.

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

23.   The various states of an interface:

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.

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

25.   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).

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

27.    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.

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

29.   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.

30.   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.

31.   IP provides no form of error correction/acknowledgements.

32.   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.

33.   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.

34.   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.

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

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

37.   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