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Chapter 4 – IP

Chapter 4 – IP. What is IP?. IP – Internet Protocol IP is a datagram packet-switching protocol that provides for connectionless, unreliable delivery of frames Current version of IP in use today is version 4 New version of IP is called IP version 6. Services offered by IP.

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Chapter 4 – IP

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  1. Chapter 4 – IP

  2. What is IP? • IP – Internet Protocol • IP is a datagram packet-switching protocol that provides for connectionless, unreliable delivery of frames • Current version of IP in use today is version 4 • New version of IP is called IP version 6

  3. Services offered by IP • Internetworking protocol • Multiple client protocols • Datagram delivery • Fragmentation and reassembly • Datagram packet-switched protocol

  4. Internetworking Protocol • Allows for the creation of an IP internetwork – two or more networks interconnected by IP routers • Routable protocol • IP header contains source and destination IP addresses for routing the packet

  5. Multiple Client Protocols • IP is an internetwork carrier for upper layer protocols • IP can carry different upper layer protocols, but each IP packet only carries data from one upper layer protocol at a time • The packet does indicate what upper layer protocol is being carried so data can get to the correct layer at the destination • Client and server must use the same upper layer protocol • Examples of upper layer protocols: TCP, UDP

  6. Datagram Delivery • Connectionless – no handshaking occurs between source and destination prior to sending data • No logical connection is created between source and destination • Unreliable – Packets are sent without sequencing and without requiring an acknowledgement • End-to-end reliability is responsibility of upper layer protocols such as TCP

  7. Fragmentation & Reassembly • IP allows for the fragmentation of the payload when forwarding onto a link that does not support the current size of the datagram • Routers and sending host fragment the paylaod • The destination reassembles the fragments into the original payload

  8. Datagram packet-switched technology • Each router makes an independent routing decision and forwards the packet • Each packet can take a different path between the source and destination • The router uses IP address of destination to make the routing decision

  9. IP Maximum transmission Unit (MTU) for Common Network Layer Technologies • Ethernet II –1500 bytes • FDDI - 4352 bytes • Fragmentation can occur when crossing a router from a link with a higher MTU to a link with a lower MPU

  10. Format of the IP Datagram • Header – between 20 and 60 bytes • Payload – between 8 bytes and 65,515 bytes

  11. Some Fields in the IP Header • Version – 4 bits – Standard IP version is 4. There is a new version (6) • Type of Service – 8 bits – Indicates quality of service with which this datagram is to be delivered. Routers normally ignore the values in the TOS field • Total length – indicates the size of the IP datagram • Identification – used to number the the fragments of an original IP datagram • Time To Live – Indicates how many links the datagram can travel before an IP router discards it

  12. Fields in IP Header – Cont. • Protocol – Indicates upper layer protocol contained within the IP payload – TCP is indicated by 6 • Checksum – 2 bytes – provides checksum on the IP header only. The payload must provide their own checksums. This value changes with each router. Why? (TTL)

  13. See Example of Fragmentation • P. 87 • See fragmentation fields • Note use of Identification field • Note use of Fragment Offset

  14. Avoiding Fragmentation • Fragmentation and reassembly is very expensive • On Internet, fragmentation is discouraged • How to avoid fragmentation • Set the DF flag to 1 on all datagrams sent • Discover the IP MTU that is supported by all the links in the path between the source and destination

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