CMSC 137 - Internet Protocol

Internetworking

The process of connecting multiple Local Area Networks (LANs) to form a larger network, such as the Internet, using the network, data link, and physical layers to enable communication between devices across different networks.

Network Layer

The layer in the TCP/IP or OSI model responsible for routing packets from the source to the destination across multiple networks, performing tasks such as packetizing, routing, and forwarding.

Datagram Approach

A packet-switching method used by the Internet where data is divided into independent packets (datagrams) that may take different paths to the destination, treated individually by routers.

Universal Addressing

A system in the network layer that assigns globally unique IP addresses to devices, enabling accurate routing of packets from source to destination across the Internet.

Connectionless Communication

A communication model in the network layer where each packet is sent independently without establishing a dedicated connection, allowing flexible but potentially out-of-order delivery.

IPv4

a 32-bit addressing protocol in the TCP/IP suite’s network layer, responsible for routing packets using a header with fields like version, header length, and checksum.

IPv4 Datagram

The basic unit of data in IPv4, consisting of a header (containing control information like source and destination addresses) and a payload (data from higher layers).

Version (VER) Field

A 4-bit field in the IPv4 header that specifies the protocol version, set to 4 for IPv4.

Header Length (HLEN) Field

A 4-bit field in the IPv4 header that indicates the length of the header in 4-byte words, typically 5 (20 bytes) without options, up to 15 (60 bytes) with options.

Differentiated Services

An 8-bit field in the IPv4 header (formerly service type) used to specify quality of service (QoS) requirements, such as priority or specific handling for packets.

Precedence Subfield

A 3-bit subfield within the IPv4 differentiated services field that defines the priority of a datagram (0–7), used for managing network congestion.

Type of Service (TOS) Bits

A 4-bit subfield in the IPv4 header specifying QoS preferences: 0000 (normal), 0001 (minimize cost), 0010 (maximize reliability), 0100 (maximize throughput), 1000 (minimize delay).

Codepoint Subfield

The first 6 bits of the IPv4 differentiated services field, defining service types; when the 3 rightmost bits are 0, the 3 leftmost bits act as precedence; otherwise, it defines 64 services assigned by Internet or local authorities.

Total Length Field

A 16-bit field in the IPv4 header that specifies the total length of the datagram (header + data) in bytes, up to 65,535 bytes.

Identification Field

A 16-bit field in the IPv4 header that uniquely identifies a datagram, used to reassemble fragments if the datagram is split due to MTU constraints.

Flags Field

A 3-bit field in the IPv4 header for fragmentation control: 1st bit (reserved), 2nd bit (do not fragment, if set, packet cannot be fragmented), 3rd bit (more fragments, set to 1 except for the last fragment).

Fragmentation Offset Field

A 13-bit field in the IPv4 header that indicates the position of a fragment relative to the original datagram, measured in 8-byte units.

Time to Live (TTL) Field

An 8-bit field in the IPv4 header that limits the number of hops (routers) a datagram can traverse, decremented by each router; the packet is discarded if it reaches 0.

Protocol Field

An 8-bit field in the IPv4 header that identifies the higher-level protocol (e.g., ICMP = 1, IGMP = 2, TCP = 6, UDP = 17, OSPF = 189) to which the datagram’s payload is passed.

Checksum Field

A 16-bit field in the IPv4 header used for error checking of the header only, calculated by summing 16-bit words, wrapping the sum, and taking the one’s complement.

Source Address Field

A 32-bit field in the IPv4 header that specifies the IPv4 address of the sender of the datagram.

Destination Address Field

A 32-bit field in the IPv4 header that specifies the IPv4 address of the intended recipient of the datagram.

Options Field

A variable-length field (up to 40 bytes) in the IPv4 header used for network testing and debugging, including options like no operation, end of option, record route, strict/loose source route, and timestamp.

No Operation Option

A 1-byte option in the IPv4 header used as a filler between other options for alignment purposes.

End of Option

A 1-byte option in the IPv4 header used for padding to mark the end of the options field.

Record Route Option

An IPv4 header option that records the addresses of up to 9 routers that handle the datagram, used for debugging network paths.

Strict Source Route Option

An IPv4 header option that specifies the exact sequence of routers a datagram must follow, used for testing or security purposes.

Loose Source Route Option

An IPv4 header option that suggests a list of routers to visit but allows the datagram to pass through other routers as well.

Timestamp Option

An IPv4 header option that records the time a router processes the datagram, used to measure network latency.

Maximum Transfer Unit (MTU)

The maximum size of the data field in a data link layer frame, defined by the protocol (e.g., Ethernet: 1,500 bytes, PPP: 296 bytes), requiring fragmentation if a datagram exceeds this size.

Fragmentation

The process of dividing an IPv4 datagram into smaller fragments to fit within a network’s MTU, with each fragment carrying its own header and reassembled at the destination.

IPv6

a 128-bit addressing protocol designed to overcome IPv4’s limitations, such as address depletion, and to support real-time transmission and security (IPsec).

Address Depletion

The exhaustion of IPv4’s 32-bit address space (~4.3 billion addresses), a key reason for developing IPv6 with its 128-bit address space (~340 undecillion addresses).

IPv6 Packet

The basic unit of data in IPv6, consisting of a fixed 40-byte base header (with fields like version, traffic class, and source/destination addresses) and a payload (data and optional extension headers).

IPv6 Base Header

A fixed 40-byte header in an IPv6 packet containing fields: version (6), traffic class, flow label, payload length, next header, hop limit, source address (128 bits), and destination address (128 bits).

Traffic Class Field

An 8-bit field in the IPv6 header that specifies quality of service (QoS) requirements for different payload delivery needs, similar to IPv4’s TOS.

Flow Label Field

A 20-bit field in the IPv6 header that identifies packets belonging to the same data flow (e.g., a video stream), enabling routers to provide consistent handling.

Payload Length Field

A 2-byte field in the IPv6 header that specifies the length of the datagram’s payload (excluding the base header), up to 65,535 bytes.

Next Header Field

An 8-bit field in the IPv6 header that indicates the type of the first extension header (e.g., fragmentation) or the payload’s protocol (e.g., TCP, UDP).

Hop Limit Field

An 8-bit field in the IPv6 header that limits the number of routers a packet can traverse, decremented by each router; the packet is discarded if it reaches 0 (equivalent to IPv4’s TTL).

Extension Headers

Optional headers in IPv6 that replace IPv4’s options, used for additional functionality like fragmentation, routing, or security, placed between the base header and payload.

Dual Stack

A transition strategy where a device runs both IPv4 and IPv6 protocols simultaneously, allowing communication with both IPv4 and IPv6 systems during the transition period.

Tunneling

A transition strategy where IPv6 packets are encapsulated in IPv4 packets to travel over IPv4 networks, extracted at the exit point to continue on IPv6 networks.

Header Translation

A transition strategy that converts IPv6 packets to IPv4 packets (or vice versa) for compatibility, involving steps like extracting IPv4 addresses from IPv6 mapped addresses and calculating IPv4 checksums.

IPv6 Mapped Address

An IPv6 address format that embeds an IPv4 address in the rightmost 32 bits, used during header translation to enable communication between IPv6 and IPv4 systems.