Internet protocols are standardized rules for formatting data and taking network actions so devices can communicate. The phrase can mean the wider family of protocols used on the internet. Internet Protocol, or IP, is one protocol in that family: it addresses and routes packets across networks toward their destination.
“TCP/IP” is a useful label for a protocol suite, but IP and TCP do different work. IP handles cross-network addressing and routing. IP can be used with transport protocols including TCP and UDP, which govern different aspects of sending and receiving data.
Internet protocols, separated by job
A protocol is an agreed format and procedure. Without that agreement, one system cannot reliably interpret what another sends.
- IP: addresses packets and routes them between networks. It is a network-layer protocol for moving packets from a source interface to a destination interface across IP networks.
- TCP: a transport protocol that opens a connection, uses acknowledgements, and seeks to deliver packets in order. When receipt is not acknowledged, TCP retransmits missing packets.
- UDP: a transport protocol that does not establish a connection or ensure that packets are delivered and in order.
- ICMP: Internet Control Message, a separately identified protocol in IP’s assigned protocol-number registry.
IP can be used with both TCP and UDP. TCP is one transport companion for IP, not the whole of it.
A packet’s journey through IP
Data moving across the internet is divided into packets. An IP packet has a header and a payload, the data being carried. The header includes source and destination IP addresses plus other information used to handle the packet.
Routers use destination addressing and routing tables to forward packets across interconnected networks. A packet can pass through several networks on the way to the network responsible for its destination address. Once it arrives, the receiving system handles it according to the transport protocol used with IP.
TCP supplies delivery behavior that IP does not provide by itself, including connection setup, acknowledgements, retransmission of missing packets, and in-order delivery. UDP omits connection setup and does not ensure delivery or ordering.
A simplified packet sequence
- A system prepares data for transmission.
- TCP or UDP supplies transport behavior for the data.
- IP adds source and destination addressing and identifies the next-level protocol.
- Routers forward the packet between networks using the destination IP address and routing tables.
- The destination handles the packet using the indicated transport protocol.
The header identifies what comes next
Protocols can carry other protocols. In IPv4, the IP header has an 8-bit Protocol field that identifies the next-level protocol. IPv6 calls the corresponding field Next Header. IANA publishes the assigned protocol-number registry, whose registration procedures require IESG approval or standards action.
The registry lists ICMP as protocol number 1, TCP as 6, and UDP as 17. Those identifiers distinguish the next-level protocol carried by IP.
IPv4 and IPv6 are versions of IP
IPv4 and IPv6 are versions of the Internet Protocol. Both identify what follows IP, though IPv4 calls the relevant field Protocol and IPv6 calls it Next Header.
The useful mental model is straightforward: protocols are shared rules; IP supplies cross-network addressing and routing; TCP and UDP provide different transport behavior; and IP header fields identify the next protocol for handling the packet.
Frequently asked questions
How do TCP and UDP differ?
TCP opens a connection, uses acknowledgements, seeks in-order delivery, and retransmits missing packets when receipt is not acknowledged. UDP does not establish a connection or ensure delivery and ordering.
What is the difference between IPv4 and IPv6?
IPv4 and IPv6 are versions of the Internet Protocol. In IPv4, the field that identifies the next-level protocol is called Protocol; IPv6 calls the corresponding field Next Header.
How do routers use IP addresses to forward packets?
IP packets include destination IP addresses in their headers. Routers use routing tables and destination addressing to forward packets across interconnected networks toward the destination network.
Sources
- What is the Internet Protocol? — www.cloudflare.com
- Internet Protocol — en.wikipedia.org
- Assigned Internet Protocol Numbers — www.iana.org
