ICND1 - 4. Understanding TCP/IP

What is special about IP address 127.0.0.1?

127.0.0.1 is the loopback address. The loopback address is used to test the proper installation of the IP stack.

What are the port numbers for FTP?

20 and 21 FTP uses port 20 for data transfer and port 21 is the command port.

What is the port number for SSH?

22

What is the port number for Telnet?

23

What is the port number for SMTP?

25

How many hosts are available for use in a default Class C network?

254 hosts are available. A default Class C network uses 8 bits for host addresses. Thus 2^8 - 2 = 254.

How many usable IP addresses are provided in a default Class C network address?

254 usable IP addresses are provided. The default subnet mask for a Class C address is 255.255.255.0, or /24. This means that 24 bits are used for the network number and 8 bits are reserved for hosts. 2^8 = 256. However, because two addresses are reserved for the network address and broadcast address, the amount of usable IP addresses is 254. The formula to calculate usable IP addresses is 2n-2, where n is the number of host bits.

What is the port number for DNS?

53

How many hosts are available for use in a default Class B network?

65,534 addresses are available. A default Class B network uses 16 bits for host addresses; thus 2^16 - 2 = 65,534.

What is the port number for TFTP?

69

What is a TCP window?

A TCP window determines the number of segments that can be sent before an acknowledgment is required. Note TCP uses a "sliding window" technique to specify the number of segments that the recipient can accept. Sliding means that the window size is negotiated dynamically during the TCP session.

What is a TCP/IP socket?

A TCP/IP socket is an IP address combined with a TCP or UDP port number. When a host wants to talk to another host, it sends its IP address along with the application (port number) it wants to communicate with. For example, if host 192.168.0.3 wants to talk to host 192.168.0.2 by email, host 192.168.0.3 sends its IP address and destination port number (192.168.0.3:1023) to host 192.168.0.2 with the port number it wants to communicate with (192.168.0.2:25).

An IP address is a hierarchical address that consists of what two parts?

An IP address is a hierarchical address that consists of the following two parts: Network ID: Describes the network to which the IP address or device belongs Host ID: The ID that identifies a specific host Note IP addresses include the use of a subnet mask that is responsible for deciphering which part of the IP address is the network and which part is the host.

What is an IP address used for?

An IP address uniquely identifies a device on an IP network.

Convert the decimal number 167 to binary.

Binary uses only two symbols (1 or 0) instead of ten symbols like decimal. In binary, 1 signifies ON and 0 signifies OFF. To convert a decimal number to binary, each digit represents the number 2 raised to a power exponent based on its position. To convert a decimal number to binary, first find the largest power of 2 that can fit into the decimal number. If you have the decimal number 167, 128 is the largest power of 2 that fits into this binary number, so 128 is considered ON. Subtracting 128 from 167 leaves you with 39. The next largest power that can fit into 39 is 32, so 32 is considered ON. Subtracting 32 from 39 leaves you with 7, so 4, 2, and 1 are considered ON. This leaves you with the following binary number: 10100111.

What is CIDR?

Classless interdomain routing (CIDR) is an addressing scheme for the Internet that allows more efficient use of IP addresses than the old Class A, B, and C scheme. It is more flexible and offers route aggregation (supernetting). A CIDR address is a network address that does not use original Class A, B, and C rules. For example, a CIDR address can look like this: 192.168.2.0/29.

Convert the binary number 01100100 to decimal.

Converting a binary number to decimal is just the reverse of converting a decimal number to binary. When converting from binary, look at the numbers that are considered ON and then find their place value. In the binary number 01100100, the place values 64, 32, and 4 are ON. If you add these place values together, you get the decimal number of 100.

Convert the binary number 0101011011000010 to hexadecimal.

Converting binary to hex is easier than it looks. No matter how large the binary number, always apply the following conversion: Break the binary number into groups of four, starting from the right and moving left. If the binary number is not divisible by four, add 0s to the left end or until you have four digits in every group. Using this equation, 0101011011000010 is broken into the following groups: 0101 0110 1100 0010. After you have created the groups, you can convert the digits to hex. 0101 is 5 in hex, 0110 is 6, 1100 is C, and 0010 is 2, so this binary number looks like the following in hex: 0x56C2.

What protocol(s) and port numbers does DNS use?

DNS uses both TCP and UDP using port number 53. DNS uses UDP to carry simple queries and responses and TCP to guarantee the correct and orderly delivery of large amounts of bulk data between DNS servers for synchronization of databases.

What is the purpose of flow control?

Flow control provides a mechanism for the receiver to control the transmission speed. TCP implements flow control by using the SYN and ACK fields in the TCP header, along with the Window field. The Window field is a number that implies the maximum number of unacknowledged bytes allowed to be outstanding at any time.

What is the Internet Protocol (IP)?

IP is a connectionless protocol that provides best-effort delivery and routing of packets. IP has the following characteristics: Operates at Layer 3 (network) of the Open Systems Interconnection (OSI) reference model and the Internet layer of the TCP/IP (Internet) model. Is connectionless, providing best-effort delivery of packets. Uses hierarchical addressing. Has no built-in data recovery. Each packet is treated independently; thus each packet can travel a different way to its destination. Operates independently of the medium that is carrying the data.

How many bits are in an IPv4 address? In an IPv6 address?

IPv4: 32 bits IPv6: 128 bits

A host computer has been correctly configured with a static IP address, but the default gateway is incorrect. Which layer of the OSI model is first affected by this misconfiguration?

Layer 3 is affected first. The default gateway sends IP packets to a remote network and functions at Layer 3 of the OSI model.

What does RFC 1918 define?

RFC 1918 defines reserved (private) networks and addresses that are not routed on the Internet. These addresses are as follows: 10.0.0.0 to 10.255.255.255 172.16.0.0 to 172.31.255.255 192.168.0.0 to 192.168.255.255 They are used as internal private addresses within a corporation or home network. Private addresses are widely used today, and they employ mechanisms such as Network Address Translation (NAT) and Port Address Translation (PAT) to assist with "stretching" the current IPv4 address space. This stretching is done by translating private IP addresses to public routable IP addresses on the Internet, thus ensuring that private hosts can communicate externally without having a public IP address directly configured.

What is reliable versus best-effort delivery?

Reliable delivery is connection oriented, and best-effort is connectionless.

What does route aggregation mean when referring to VLSM?

Route aggregation means combining routes to multiple networks into one larger IP network or aggregated IP subnets within the class rules.

What is session multiplexing?

Session multiplexing is a process that allows a host with a single IP address to support multiple sessions simultaneously. A session is created when a source host needs to send data to a destination host.

Which has more overhead: UDP or TCP?

TCP has more overhead. Because UDP segments are not acknowledged, they do not carry the overhead that TCP does, thus allowing faster transmissions.

How do TCP and UDP perform segmentation?

TCP performs segmentation by taking data chunks from applications and breaking them into smaller segments that will fit in the maximum transmission unit (MTU) of the underlying network layers. UDP does not perform segmentation; instead it expects the application process to send data in correct sizes.

How do TCP/IP protocols identify applications?

TCP/IP protocols identify applications through port numbers.

What is the IP protocol number for TCP and UDP?

TCP: 6 UDP: 17 Note IP protocol numbers are the link in the IP header that points to upper-layer protocols such as TCP and UDP.

What is DNS?

The Domain Name System (DNS) converts domain names or host names into IP addresses. Instead of having to remember a host's IP address, DNS allows you to use a friendly name to access the host. For example, it is easier to remember http://www.cisco.com than 198.133.219.25.

What is the correct network address for host 192.168.10.72/26?

The correct network address is 192.168.10.64. A 26-bit subnet mask is 255.255.255.192. A quick way to find the network of a given subnet mask is to subtract the last portion of the subnet mask from 256. In this case, 256 - 192 = 64. Assuming that the ip subnet zero command is enabled on the router, the usable networks for a 26-bit subnet mask are as follows: 192.168.10.0 192.168.10.64 192.168.10.128 192.168.10.192 Host 192.168.10.72 falls in the 192.168.10.64 network.

What is the purpose of the default gateway?

The default gateway allows hosts to communicate with hosts that are on a different network segment. All data that is not destined for the same network of the sending device is sent to the default gateway for delivery.

If an IP addressed device wants to communicate with all devices on the local network, what is the destination IP address of its broadcast?

The destination IP address is 255.255.255.255. This address is also called the local broadcast address.

What are the different classes of IP addressing and the address ranges of each class?

The different classes of IP addressing and their ranges are as follows: Class A: 1.0.0.0 to 126.255.255.255 Class B: 128.0.0.0 to 191.255.255.255 Class C: 192.0.0.0 to 223.255.255.255 Class D: 224.0.0.0 to 239.255.255.255 (Multicasting) Class E: 240.0.0.0 to 255.255.255.254 (Reserved) Note 127.0.0.0 is also a Class A network, but it is reserved for the loopback, or "localhost," IP—the IP address of the TCP/IP software itself.

What is the range of binary values for the first octet in Class B addresses?

The first octet for a Class B IP address is 128-191 in decimal, which is 10000000-10111111 in binary. If you see similar questions on the ICND 1 exam, remember the following: Class A addresses always have the high-order bit as 0. For example, 0xxxxxxx. Class B addresses always have the high-order bit as 1 and the second bit as 0. For example, 10xxxxxx. Class C addresses always have the high-order bit and second bit as 1. The third bit is 0. For example,110xxxxx.

What are the five types of reserved IPv4 addresses?

The five reserved IPv4 addresses are Network address: The address of the network is an IP address that has binary 0s in all the host bit positions. Direct broadcast address: An address for each network that allows communication to all hosts on a network. The direct broadcast address has all 1s in the host bit positions. Local broadcast address: Used to allow hosts to communicate with all hosts on a local network. The address used is 255.255.255.255. Local loopback address: Used to let the system send a message to itself for testing. This address is 127.0.0.1. All zeros address: Used to indicate hosts in "this" network and used only as a source address.

What are the most common fields that are included in the TCP header?

The most common used fields included in the TCP header are as follows: Acknowledgment Number Sequence Number Source/Destination Port Window Size TCP Checksum

What is the purpose of TCP sequencing?

The purpose of sequencing is to provide reliability by requiring the recipient to acknowledge receipt of a group of segments before a timer expires. Sequencing is also used to provide proper ordering or segments.

What are the steps for the TCP three-way handshake?

The steps of the TCP three-way handshake are as follows: 1. The source host sends a SYN to the destination host. 2. The destination host replies to the source with an ACK. At the same time, it sends a SYN to the source host. 3. The source host replies with an ACK. Note For the exam, remember: Step 1: SYN, Step 2: SYN/ACK, Step 3: ACK.

What is the role of the subnet mask in an IP network?

The subnet mask identifies the network and host portion of an IP address. It is used by hosts to identify the destination IP address as either local or remote and is also used by routers to determine the path to route packets.

As a network administrator, you have a Class B address. Assuming that the ip subnet zero command is enabled on the router, what subnet mask allows you to have 100 subnetworks with at least 500 usable hosts?

The subnet mask is 255.255.254.0. 255.255.254.0 in binary is as follows: 11111111.11111111.11111110.00000000 All you care about are the last two octets. So you have 7 bits for the network and 9 bits for host addresses. Seven bits of subnetting provide 128 subnets, and 9 bits of host subnetting provide 510 hosts per subnet.

Your Internet provider has given you the IP network address of 172.16.0.0/16. You have 18 networks, each with 1200 hosts. You want to assign one IP range per subnet, leaving room for future growth. Assuming that the ip subnet zero command is enabled on all routers, what subnet mask would best achieve your goals?

The subnet mask of 255.255.248.0 would best achieve your goals. If you look at this subnet mask in binary, you can see that you have 5 subnet bits for the network address: 11111111.11111111.11111000.00000000 If you use the subnet equation 2^5 = 32, 32 available networks will be provided with the subnet mask, which fulfills the requirement for 18 networks and allows adequate growth. This leaves you with 11 bits to be assigned to hosts. This gives you 2046 (2^11 - 2) addresses, giving you more than enough IP addresses to be assigned to hosts. If you use a subnet mask of 255.255.240.0, you will meet the requirement of 1200 hosts (2^12 - 2 = 4094 available hosts) but not have enough networks (2^4= 16 available networks).

What are the three mechanisms TCP uses to accomplish a connection-oriented connection?

The three mechanisms TCP uses to accomplish a connection-oriented connection are as follows: Packet sequencing Acknowledgments, checksums, and timers Windowing

What is the purpose of the TCP three-way handshake?

The three-way handshake creates a connection-oriented virtual circuit between two devices, and establishes an initial sequence number and window size.

What functions does the transport layer perform?

The transport layer performs the following functions: Session multiplexing Identification of different applications Segmentation Flow control Connection-oriented Reliability

In a default Class A network, how many octets are used for host addresses?

Three octets are used for host addresses. One octet consists of 8 bits; thus a default Class A network uses 24 bits for host addresses. The maximum number of hosts a Class A network can have is 16,777,214 (2^24 - 2).

What is the purpose of TCP and UDP port numbers?

To pass information (such as email) to upper layers, TCP and UDP use port numbers. These port numbers are predefined and keep track of different conversations among different hosts at the same time. Originating source port numbers are dynamically assigned by the source host using a number in the range of 49,152 to 65,535.

On a Windows computer, what commands do you use to release an IP address obtained from DHCP and request a new address?

To release the IP address: ipconfig /release To request a new address: ipconfig /renew

What two common protocols function at the transport layer of the TCP/IP model?

Two protocols that function at the transport layer of the TCP/IP model are as follows: TCP (Transmission Control Protocol): A connection-oriented, reliable protocol UDP (User Datagram Protocol): A connectionless and unacknowledged protocol Note TCP deals with the three-way handshake. Reliability deals with acknowledgments (ACK) and NAKs. TCP uses ACKs and NAKs that are used by other protocols if there is a problem. UDP is characterized as connectionless and does not include a mechanism to guarantee data delivery. UDP uses a best-effort delivery and, on most networks today, can send a packet with minimal to no packet loss without the overhead of TCP.

What transport layer protocols are best suited for the transport of VoIP data?

UDP and RTP are best suited. VoIP uses a combination of UDP and RTP for transport of data. VoIP is time sensitive and uses UDP because UDP uses less overhead than TCP.

What are the benefits of variable-length subnet masking (VLSM)?

VLSM gives a network administrator the option of including more than one subnet mask within a network and of subnetting an already subnetted network address. VLSM benefits include More efficient use of IP addresses: Without VLSM, companies must implement a single subnet mask within an entire Class A, B, or C network number. Better-defined network hierarchical levels: VLSM allows more hierarchical levels within an addressing plan and allows aggregation of network addresses.

What are well-known port numbers?

Well-known port numbers are used for fundamental applications such as email and DNS. They have a range from 0 to 1023.

On a Windows computer, what command can you use at the command prompt to view the IP information assigned to the PC?

You can use the ipconfig command.

How many usable subnets and usable hosts do you have if you subnet the network address 192.168.1.0 with the subnet mask 255.255.255.240?

You have 16 subnets with 14 hosts in each network. If you subnet 192.168.1.0 with a 28-bit mask (255.255.255.240), you have 16 networks with 14 hosts in each network. If you look at the network address and subnet mask in binary, you can see that in the last octet, you have 4 bits for networks and 4 bits for hosts, as follows: 11000000.10101000.00000000.00000000 11111111.11111111.11111111.11110000 You can apply these bits to the following formula, where x is the amount of borrowed bits: Amount of subnets = 2^x Amount of hosts = 2^x - 2 Therefore, 2^4 - 2 = 14 subnets. You can then apply the same equation to determine that the number of hosts is also 14.