Networking Concepts Quiz

Course Information

• Course Number: CS461
• Course Title: Computer Networks
• Topic: Internet and Transport Protocols
• Covered Topics: Internet, Internetworking, IP, IP Addresses, Internet Apps, TCP, Application

Contents

• Course Content includes: Internetworking, The Internet Protocol, IP Addressing, Internet Applications, Transmission Control Protocol, Application Layer Protocols, LANs and WANs, and Connecting Multiple LANs and WANs
• Various concepts and topics regarding Computer Networks are covered in CS461

LANs and WANs

• LANs (Local Area Networks):
  • Different types, topologies, and technologies.
  • Operate at layers 1 and 2 (Physical and Data Link Layer) using switches and hubs.
  • Connected by bridges
• WANs (Wide Area Networks):
  • Connect LANs over a large distance.
  • Employ point-to-point links (e.g., ADSL, PDH) or networks (e.g., ATM, SDH, telephone) using packet or circuit switching.
  • Devices connecting WAN to LAN need to support both technologies.
  • Primarily operate at layers 1 and 2.

Connecting Multiple LANs and WANs

• Organizations require various network technologies.
• Aim: allow any computer to communicate with any other computer, regardless of their LAN/WAN connection.
• Internetworking: connecting the many types of networks (LANs/WANs) together.
• An internetworking protocol supports data delivery across different networks.
• Example: Internet Protocol (IP)

Internetworking with Routers

• Internetworking is accomplished using routers.
• Routers connect two or more LANs or WANs.
• Routers are packet switches that operate at the network layer.

The Internet Protocol (IP)

• The core internetworking protocol for the Internet.
• Implemented in hosts and routers.
• Features:
  • Datagram packet switching
  • Connectionless
  • Addressing
  • Fragmentation-and-reassembly
• IP version 4 (IPv4) is most prevalent; IPv6 is available.
• IP does not provide:
  • Connection control
  • Error control
  • Flow control (TCP)
  • Status reporting (ICMP)
  • Priority, QoS (DiffServ, IntServ)
  • Security (IPsec)

Terminology

• Routers: Nodes connecting networks (LANs/WANs); operate at the network layer.
• Subnetworks: Individual networks (LANs and WANs).
• Internetworking: Connects two or more networks using routers, creating an internetwork/internet.
• The Internet: A global internetwork using IP.
• Routing: Locating a path from source to destination across a network.
• Forwarding: Moving data along a network path.
• Packet Switch: A generic device performing switching in a packet switching network; routers are packet switches at the network layer.
• Circuit Switch: A generic device performing circuit switching in a circuit switching network
• Ethernet switch: An IEEE 802.3 switch (Ethernet, Fast Ethernet, or Gigabit Ethernet) that operates at the data link layer.

IP Datagram

• Variable-length header and variable-length data.
• Header (20 Bytes): Required fields and optional fields (may reach 60 bytes).
• Data: Multiple of 8 bits. Max size: 65,536 bytes.
• Field details include Version, Header Length, DiffServ/ECN, Identification, Time to Live, Protocol, Flags, Total Length, Fragment Offset, Header Checksum, Source IP Address, Destination IP Address, Options, Padding.

IP Datagram Fields

• Version (4 bits): Current value = 4 (IPv4)
• Header Length (4 bits): Measured in 4 byte words.
• DiffServ (6 bits): Used for quality of service.
• ECN (2 bits): Used for congestion notification.
• Total Length (16 bits): Length of the entire datagram (including the header) measured in bytes.
• Identification (16 bits): Sequence number for datagrams.
• Flags (3 bits): Used for fragmentation and reassembly.
• Fragment Offset (13 bits): Information about fragmented packets.
• Time To Live (8 bits): Datagram lifetime.
• Protocol (8 bits): Identifies the next higher layer protocol.
• Header Checksum (16 bits): Error-detecting code.
• Source and Destination Addresses (32 bits each): IP addresses of source and destination hosts.
• Options: Variable-length fields.
• Padding: Ensures datagram length is a multiple of 4 bytes.
• Data: Variable length containing data to be transmitted.

IP Routing and Forwarding

• Routing Tables: Store destination addresses and next node. Created manually or by routing protocols.
• Routing Protocols: Collect network information, calculate least cost paths, and update routing tables. Adaptive protocols (OSPF, RIP, EIGRP, BGP).
• Forwarding: Routers relay IP datagrams from the source to the destination host, based on destination addresses in routing tables.

Other Features

• IP includes:
  • Fragmentation and reassembly (fragmentation on source and reassembly on destination).
  • Time to Live (TTL).
  • ICMP (error reporting, ping).
  • ARP (mapping IP addresses to Ethernet addresses).
  • IPv6
  • Multicasting
  • Quality of Service (DiffServ)
  • Mobility (Mobile IP)
  • Security (IPsec)

IPv4 Addresses

• 32 bits long
• Split into network and host portions
• Network portion: identifies the subnet.
• Host portion: identifies the specific device (host/router) within that subnet.
• All subnets have unique network portions.
• Devices in the same subnet have the same network portion but different host portions.
• Classful, subnet, and classless addressing schemes (focus on classless addressing)
• Why split? Allows hierarchical addressing, making routing in the Internet scalable.

Representing IPv4 Addresses

• Written in dotted decimal notation (e.g., 192.168.1.1).
• Each part represents a byte.

Classless IP Addressing

• Subnet masks or address masks identify the split between network and host portion in an IP address.
• 32 bits long
• Bit 1 in the mask indicates network portion; Bit 0 indicates host portion.
• Represented in dotted decimal form or shortened form (counting the number of 1 bits from left).

Special Case IP Addresses

• Network Address: All bits in the host portion are 0 (identifies a subnet).
• Directed Broadcast Address: All bits in the host portion are 1 (sent to all hosts on a specific subnet).
• Local Broadcast Address: Identifies all hosts on the current subnet.
• Loopback Address: Identifies the current host (e.g., 127.0.0.1, also called localhost).
• Start-up Source Address: Identifies a host that does not yet have an assigned address (all bits are 0).
• Selected Addresses: Reserved for private networks (not connected to the Internet; behind NAT). Ranges include 10.0.0.0-10.255.255.255, 172.16.0.0-172.31.255.255, 192.168.0.0-192.168.255.255

Obtaining an IP Address

• IANA (Internet Assigned Numbers Authority) manages IP address assignment.
• IANA delegates IP network ranges to regional and national authorities.
• Organizations obtain addresses from national/local registries.
• Organizations can freely assign addresses within their allocated block.
• Manual IP configuration is possible, but automatic configuration via protocols like DHCP is more common.

Internet Applications

• Most follow a client/server model.
• Server waits for client to initiate communication.
• Client initiates communication. Data can flow in both directions.
• Examples: web browsers, email clients, instant messaging clients, and various other applications.

Issues with Client/Server Applications

• How to simplify application programming without needing in-depth communication details?
• Employing transport protocols (e.g., TCP and UDP) to implement common functions across applications.
• Facilitating communication between applications written in different languages and operating systems using common APIs like Sockets.
• Distinguishing various applications residing on the same computer utilizing port numbers.

Transport Protocols

• Transfer data between application processes at different hosts

• End-to-end communications

• Transmission Control Protocol (TCP):

  • Widely used, connection-oriented, error control, flow control, and congestion control.
  • Connection-oriented: Establishes a connection before data transfer.
  • Stream-oriented: Treats data as a continuous stream of bytes; uses sequence numbers.
  • Full duplex: Data can flow in both directions.
  • Flow and error control: Go-Back-N style.

• User Datagram Protocol (UDP): Older protocol, connectionless

  • Domain-specific protocols

• Other transport protocols: SCTP, DCCP

TCP Segment

• Header (20 bytes): Includes source and destination ports, sequence numbers, acknowledgment numbers, window size (flow control), checksum (for error checking), and urgent pointer (for critical data).
• Optional fields and padding
• Fields detailed as follows: Length, Reserved, Flags, Advertised Window, Checksum, Urgent Pointer, Options and padding

TCP Segment Fields

Source/Destination ports Sequence/Acknowledgement numbers Header Length Window: flow control Checksum: error checking Urgent pointer: critical data Options: features like maximum segment size and window scaling

TCP Segment Flags

• CWR: Congestion window reduced
• ECE: Explicit congestion notification echo
• URG: Urgent data (use urgent pointer field)
• ACK: Acknowledgement (use ACK field)
• PSH: Push function
• RST: Reset connection
• SYN: Synchronize sequence numbers
• FIN: No more data from sender

TCP Connection Establishment (3-way handshake)

• Initiator selects Initial Sequence Number (ISNA).
• B acknowledges ISNA and selects its own Initial Sequence Number (ISNB); also includes acknowledgement(ACK).
• After 2 way handshake, data transfer can start; optionally the 3rd segment can contain data.

TCP Data Transfer

• Segments hold varying amounts of data.
• ACK flags used for acknowledgement. Piggybacking of ACK are common.
• Speed depends on flow control (sliding window), error control (Go-Back-N), and congestion control (sender slowing down during congestion).

Application Layer Protocols

• Various protocols support different applications.
• Examples: HTTP, FTP, SMTP, SSH, Telnet, BitTorrent, SIP, IMAP, RDP, SMB.
• Protocols for network operation: DNS, DHCP, BOOTP, NTP, SNMP.

Port Numbers

• Ports are 16-bit whole numbers used to identify applications on a host
• Source/destination port number is included in transport layer header
• Well-known ports (0-1023): Commonly used by server applications: e.g., http = 80, https = 443, ftp = 20/21, smtp = 25, dns = 53, ssh = 22, dhcp = 67/68.
• Registered ports (1024-49151): Reserved for specific servers by convention
• Dynamic ports (49152-65535): Assigned dynamically to client applications by the OS.

Additional Topics

• Unicast
• Directed Broadcast
• Local Broadcast
• Startup Source Address

Test your knowledge on essential networking concepts, including routers, transport protocols, and the role of WANs. This quiz covers various aspects of network layers, internetworking protocols, and their functionalities within a networked environment.