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What is IP (Internet Protocol)?

The network-layer protocol (the internet layer of the TCP/IP model) that uses IP addresses to deliver packets from a source host to a destination host, with routers along the way forwarding them by destination. It is best effort: it does not guarantee delivery or order, which higher layers such as TCP provide. Two versions, IPv4 and IPv6, are in use.

Japanese name: IP(インターネットプロトコル)

IP (Internet Protocol) appears in 10 practice questions across 2 topics, including Computer Networking Basics, System Architecture and Reliability.

Field: Computer Networking Basics

Try it: questions about IP (Internet Protocol)

In the four-layer TCP/IP model, which layer do TCP and UDP belong to?

  1. AApplication layer
  2. BInternet layer
  3. CTransport layer
Show answer and explanation

Answer: C. Transport layer

The TCP/IP model is described with four layers, from the bottom: the link layer (network interface layer), the internet layer, the transport layer and the application layer. TCP and UDP are transport-layer protocols, and they use port numbers to tell which application on a host the traffic is for. IP, in the internet layer, is responsible for delivering packets from one host to another. HTTP and DNS are application-layer protocols. Mapped onto the OSI reference model, the transport layer corresponds to layer 4 and the internet layer to layer 3.

Home broadband routers perform NAPT (IP masquerading), a form of NAT (Network Address Translation). What does NAPT make possible?

  1. ASeveral devices in the home can share one global IP address simultaneously to communicate with the internet, distinguished by port number
  2. BTraffic between home devices and the internet is encrypted so it cannot be eavesdropped on the way
  3. CEach device in the home is automatically assigned its own separate global IP address
Show answer and explanation

Answer: A. Several devices in the home can share one global IP address simultaneously to communicate with the internet, distinguished by port number

NAT (Network Address Translation) rewrites the source or destination IP addresses of packets passing through a router. NAPT rewrites port numbers as well as IP addresses and records the mapping between "inside address and port" and "outside port" in a translation table. This lets several devices using private addresses share the router's single global address at the same time. Returning packets are delivered to the right device by looking up the table. It only rewrites addresses and does not encrypt anything. Also, connections started from outside have no entry in the table, so they do not reach inside devices by default; hosting a server inside requires settings such as port forwarding.

IP (Internet Protocol) in the explanations

Questions that mention IP (Internet Protocol) (10)

  1. In the four-layer TCP/IP model, which layer do TCP and UDP belong to?
  2. Home broadband routers perform NAPT (IP masquerading), a form of NAT (Network Address Translation). What does NAPT make possible?
  3. On 1 Gbps Ethernet, TCP data is sent continuously with IP packets filling the 1500-byte MTU. Taking the IPv4 header as 20 bytes, the TCP header as 20 bytes, the Ethernet header and FCS together as 18 bytes, and the preamble and inter-frame gap together as 20 bytes, which is closest to the upper limit on application-data throughput?
  4. Among the ways of connecting storage, which describes a SAN (storage area network)?
  5. When a web page's data is sent, what happens on the sending side each time the data is passed from an upper layer to a lower layer?
  6. Which correctly describes the role of ARP?
  7. A host (192.168.1.10/24, default gateway 192.168.1.1) sends a packet to server 203.0.113.80 on a different network. With an empty ARP cache, whose MAC address does the host look up with ARP?
  8. Which correctly describes UDP?
  9. A full-service resolver (caching DNS server) with an empty cache looks up the IP address of www.example.com. In what order does it query servers?
  10. Which of the following does HTTPS (HTTP protected by TLS) protect?

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Related terms

Packet IP address TCP (Transmission Control Protocol) DNS (Domain Name System) HTTP (Hypertext Transfer Protocol) Ethernet UDP (User Datagram Protocol) Router LAN (local area network) ARP

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