CCNA study notes on switching methods, WAN, DOD Model

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21. The port number used by TCP is 6 and that of UDP is 17.

TCP: TCP is a full-duplex, connection-oriented protocol. It incorporates error checking as well.

UDP (User Datagram Protocol): UDP is a thin protocol. UDP is a connectionless protocol. It doesn't contact the destination before sending the packet and doesn't care whether the packet is reached at the destination. UDP uses port number 6.

22. Switching methods:

WAN (Wide Area Network)

WAN devices extend the reach of LAN (Local Area Network) devices. WANs typically span over a wide area, such over multiple cities / countries. WANs are connected over serial lines that operate at lower speeds than LANs. Some of the WAN devices are:

24. Standard adopted for Ethernet CSMA/CD by IEEE Committee is 802.3. 100BaseT (Fast Ethernet) uses IEEE803.2u standard which incorporates CSMA/CD protocol.

DOD Model

25. DOD Model maps to OSI model as below:

DoD Model

OSI Model

Process/ Application maps

Application, Presentation, Session layers (layers 7,6,5).


ISO's Transport layer (layer 4).


Network layer (layer 3)

Network Access

Data Link and Physical Layers (layers 6,7)

26. Routers can make alternate route decisions based on ICMP messages, if appropriate. Routers send an ICMP message if the destination is unreachable.

27. Port numbers are used by TCP/ UDP to set up sessions with other hosts. The following are the recommended port numbers:

28. Ethernet_II has a type field to identify the upper-layer protocol. 802.3 has only a length field and can't identify the upper-layer protocol.

29.To find valid hosts given an IP address (say and a subnet mask (sat a 12-bit subnet). The valid hosts are determined as below:

A 12-bit subnet mask gives us; 4094 subnets, each with 14 hosts. (Host addresses of all zeros and all 1s can't be assigned). The is in the 48 subnet range. The valid range is through 49 - 62. 63 is a broadcast address.

Here is how you get the subnet range:

30. The following are some important commands that can be used to edit and review command history buffer on a Cisco router. It will be useful to practice these commands.

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