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CCENT™ (Cisco Certified Entry Network Technician) Certification Exam  Notes

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16. A static route is one that is hard coded into the routing tables. Here, the destination network/host, and the next hop information are entered by hand. A static route on a Cisco router is most commonly defined by using the command:
Router(config)# ip route A.B.C.D (destination network/host) A.B.C.D (subnet mask) A.B.C.D (next hop)
You can also use the port identifier such as e0, s1 etc. to define the next hop address.
Optionally, the "distance metric" can be added at the end of the command to change the default weight.

17. A switch forms a single broadcast domain, whereas, it provides an independent collision domain for each port. Here, three ports of the switch are used, and hence it will have three collision domains. On the other hand, a Hub forms a single collision as well as a single broadcast domain. Therefore, the total number of broadcast domains in this case is two, and the total number of collision domains is four.

18. A VLAN is a group of devices on one or more logically segmented LANs. All devices working on a VLAN will have same broadcast domain. Like routers, switches (Layer 2) have the ability to provide domain broadcast segmentation called a VLAN. Using VLAN technology, you can group switch ports and their connected users into logically defined communities of interest. A VLAN operating on a Catalyst switch limits transmission of unicast, multicast, and broadcast traffic to only the other ports belonging to that VLAN, thereby controlling broadcasts.

The benefits of VLANS include:

  1. Easy Administration resulting in reduced administration costs,
  2. Increased Security due to broadcast control, if you are using simple hub, you can observe traffic corresponding to any node by simply inserting a Network analyzer.
  3. Grouping based on functional requirements irrespective of physical location of nodes,
  4. Simplify moves, adds, changes,
  5. Distribution of traffic thereby using the network bandwidth more efficiently.

19. A VTP advertisement necessarily consists of "Configuration revision number". Every time a VTP server updates its VLAN information, it increments the configuration revision number by one count. VTP clients, use the revision number to enforce the VLAN configuration Update.

20. All RIP,RIP2, and IGRP use distance vector algorithms.

  • RIP2 transmits the subnet mask with each route. This feature allows VLSM (Variable Length Subnet Masks) by passing the mask along with each route so that the subnet is exactly defined.

21. An administrative distance of 0 represents highest trustworthiness of the route.
An administrative distance of 255 represents the lowest trustworthiness of the route.

22. Anytime that you hook up two end-devices like routers, PCs, print
servers, etc. to one another, you'll need a crossover cable. A switch or hub already all have their ports crossed over, so hooking up an end-device to a switch uses a straight-through cable. When hooking up two switch ports together, you use a cross-over cable again.

23. ARP (Address Resolution Protocol): IP works at network layer. IP address is a logical address. If a packet is to be delivered to a destination machine, its physical address (MAC address) needs to be known. ARP is a protocol, which enables a machine to obtain its MAC address from a known IP address.

24. RARP (Reverse Address Resolution Protocol): RARP is used to obtain IP address from a known MAC address.

25. BooTP (Bootstrap Protocol): When a diskless workstation is powered on, it broadcasts a BootP request on the network. A BooTP server responds with its IP address, Default gateway, etc.

26. At times it may be necessary to upgrade the IOS software. You cannot load the router from Flash, and upgrade the flash at the same time. You need to load from other sources such as tftp server or ROM. To load the image from ROM, there are two ways:

  • BY using config-register 0X2101 command. This will enable the router to load the IOS from the ROM and Flash image is not used. This way we can load the upgrade to flash, and set back the configuration register to load from flash as usual after the upgrade is completed.
  • Another way is by adding the command BOOT SYSTEM ROM to the startup configuration file.

27. Boot system - This is a global command that allows you to specify the source of the IOS software image to load. If you configure more than one source, attempts are made to load the IOS from the first command in the configuration to the last successively. If the first fails, the second boot command is used.

  • Boot system rom - Loads IOS from ROM.
  • Boot system flash - Loads the first file from flash memory.
  • Boot system tftp <file name> < tftp_address > - Loads IOS with a filename <file name> from a TFTP server.

Both "copy star run" and "reload" will load Cisco router configuration into RAM.

28. By default, Cisco routers support 5 simultaneous telnet sessions. This number can be configured using ios commands.

29. By giving the command "show ip route igrp", we can see the routes found by igrp. A route discovered by igrp is denoted by letter "I" before start of the entry.

30. CDP, short for Cisco Discovery Protocol runs over Layer 2 (the data link layer) on all Cisco routers, bridges, access servers, and switches. CDP allows network management applications to discover Cisco devices that are neighbors of already known devices. CDP runs on all LAN and WAN media that support SubNetwork Access Protocol (SNAP).

31. Cisco router loads the IOS image based on the boot field and the boot system commands in the configuration. Various boot system commands are:

  1. boot system flash <IOS_filename> ;IOS image is loaded from flash memory
  2. boot system tftp <IOS_filename> <tftp_ip_address> ;Boots the system image from the TFTP server.
  3. boot system rom ; IOS is loaded from rom
  4. The command to save the running configuration to NVRAM is:
    copy running-config startup-config (write memory)

32. Class B network has the form N.N.H.H, the default subnet mask is 16 bits long. There is additional subnet mask of 7 bits long.
7 bits of subnet mask corresponds to (2^7)=128 subnets.
9 bits (16-7) of host addresses corresponds to (2^9-2)=512-2 = 510 hosts.
Some times, the subnet mask is specified with the bits available in the default subnet mask. In this case the bits available in default subnet mask is 16. Therefore, total number of bits available in the subnet mask are 16+7=23. If you are given a subnet mask of 23 bits long for a class B address, it is understood that it contains the bits from the default subnet mask as well.

Class C IP address has the form N.N.N.H. You have 8 bits available for host portion, of which 4 bits are used for subnetting. This means, you have 2^4 = 16 subnets. Similarly, you have 4 bit available for host Ids. This equals 2^4 = 16 host Ids. Out of this, host Ids of all 1s' and all 0s' are reserved. This leaves us with 14 host Ids per subnet.

33. Data Link Layer is layer 2 of OSI reference model. This layer is divided into two sub-layers:

  1. Logical Link Control (LLC) sub-layer.
  2. Media Access Control (MAC) sub-layer.

The LLC sub-layer handles error control, flow control, framing, and MAC sub-layer addressing.
The MAC sub-layer is the lower of the two sub-layers of the Data Link layer. MAC sub-layer handles access to shared media, such a Token passing or Etherne

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