Cisco^® CCNA-ICND2^™ Exam Notes

G. Miscellaneous

1. 1. ISL: A Cisco proprietary trunking protocol, associated with Ethernet. Supported by Catalyst switches and routers. ISL uses "encapsulation" of Ethernet frame for multiplexing multiple VLANs over a trunk line. 
2. 802.1Q: This is an IEEE standard for the VLAN trunking protocols, associated with Ethernet. A VLAN identifier is inserted into the frame header, a technique called frame tagging. 
3. 802.10: A Cisco proprietary method for transporting VLAN information inside the standard 802.10 FDDI frames. 
4. LANE : LANE stands for LAN Emulation and is associated with ATM. This is an IEEE standard for transporting frames over ATM networks.

2. During password recovery, the config register and NVRAM are modified. ROM holds the bootstrap code to start up the router and Flash contains the IO image.

3. Each Telnet port is known as a virtual terminal. Usually, Cisco routers support up to five virtual terminal (VTY) ports, allowing five concurrent Telnet sessions. Please note that the communication server provides more VTY ports. The virtual terminal ports are numbered from 0 through 4. The console and auxiliary ports on Cisco IOS routers and switches are asynchronous serial ports and use asynchronous protocols such as PPP, SLIP, and ARA.

4. Holddown timers prevent regular update messages from reinstating a route that has gone bad. Here, if a route fails, the router waits a certain amount of time before accepting any other routing information about that route. Holddowns tell routers to hold any changes that might affect routes for some period of time. The holddown period is usually calculated to be just greater than the period of time necessary to update the entire network with a routing change.

5. IP address: 192.168.1.1 255.255.255.240 Subnet ID: 191.168.1.0 Available Host IDs: 191.168.1.1 - 191.168.1.14 Broadcast address: 191.168.1.15
IP address: 192.168.1.17 255.255.255.248 Subnet ID: 191.168.1.16 Available Host Ids: 191.168.1.17 - 191.168.1.22
IP address: 192.168.1.36 255.255.255.224 Subnet ID: 191.168.1.32 Available Host Ids: 191.168.1.33 - 191.168.1.62

6. IP helper addresses forward a client broadcast address (such as a DHCP or BOOTP requests) to a unicast or directed broadcast address. Helper-address is required due to the fact that routers do not forward broadcasts. By defining a helper-address, a router will be able to forward a broadcast from a client to the desired server or network. There can be more than one helper-address on a network. The helper-address must to be defined on the interface that receives the original client broadcast. Note that “ip unnumbered” command is used to enable IP processing on a serial interface without assigning a specific IP address to the interface.

7. On pinging successfully, you will receive "!" symbol. This symbol is repeated 5 times, as a ping command sends 5 ICMP echo messages to the host.

8. Consider two IPs 172.24.54.0/24 and 172.24.53.0/24. The summarized route is calculated as below: 

Step 1: 
1. Take the first IP: 172.24.54.0/24: 172.24. 0 0 1 1 0 1 1 0.0 
2. Take the second IP: 172.24.53.0/24: 172.24. 0 0 1 1 0 1 0 1.0 
Note that we are not really concerned about the octets that have equal decimal values. This is because they don’t come into play while calculating summarization route, in this case. 

Step 2: 
Count the number of bits in the third octet that are aligned (or lined up) with same values. In this case 6 bits are lined up in the third octet. The summarization route is calculated by adding this number (6) to the octets preceding the third (first and second octets). Therefore, the number of bits in the summarized route is 8+8+6 = 22

Step 3: 
Calculate the decimal equivalent for third octet with 6 bits as given in the matching binary. That is 0 0 1 1 0 1 x x. Note x is because it corresponds to non matching binary number. It is equal to 128*0 + 64*0 + 32*1 + 16*1 + 8*0 + 4*1 or 32+16+4 or 52.
Therefore, the summarized route is: 172.24.52.0/22

9. Runts are packets that are smaller than the medium's minimum packet size. For example, Ethernet has a minimum allowed packet size of 64 bytes. Any packet that is less than 64 bytes in size is considered a runt in Ethernet. Giants are packets that bigger than the medium's maximum packet size. Fro example, Ethernet has a maximum allowed packet size of 1,518 bytes. Any packet that is bigger than 1,518 bytes is considered a Giant in Ethernet. CRC error occurs when the check sum calculated at the receiving end of the frame does not match with the check sum calculated at the source end. The most probable reasons for runts, giants, and CRC errors is frame collisions while traveling from source to destination. It is also possible that a network card or device is bad and generating runts and giants.

10. SONET defines interface standards at the physical layer of the OSI seven-layer model. The standard defines a hierarchy of interface rates that allow data streams at different rates to be multiplexed. SONET establishes Optical Carrier (OC) levels from 51.8 Mbps (OC-1) to 9.95 Gbps (OC-192).

11. The High Level Data Link Control protocol (HDLC) is the default encapsulation used on the synchronous serial interfaces of a Cisco router. HDLC is a Data Link layer protocol used to encapsulate and transmit packets over point-to-point links.

12. The "hello" packets are sent periodically out of each interface using IP multicast addresses. The hello interval specifies the frequency in seconds that a router sends hellos. This is 10 seconds on multi access networks.

13. The Catalyst IOS software is very similar to a router IOS. IOS image files are stored in the Flash memory on a switch.

14. The default administrative distances are as below: 

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