1 / 22

Orientation

IP. Orientation. IP (Internet Protocol) is a Network Layer Protocol. IP’s current version is Version 4 (IPv4). It is specified in RFC 891. Class A:. 0. Network (7 bits). Host (24 bits). 1. 0. Class B:. Network (14 bits). Host (16 bits). 1. 1. 0. Class C:. Network (21 bits).

warren
Download Presentation

Orientation

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. IP

  2. Orientation • IP (Internet Protocol) is a Network Layer Protocol. • IP’s current version is Version 4 (IPv4). It is specified in RFC 891.

  3. Class A: 0 Network (7 bits) Host (24 bits) 1 0 Class B: Network (14 bits) Host (16 bits) 1 1 0 Class C: Network (21 bits) Host (8 bits) IPv4 Address Model

  4. IP: The waist of the hourglass IP is the waist of the hourglass of the Internet protocol architecture Multiple higher-layer protocols Multiple lower-layer protocols Only one protocol at the network layer.

  5. Application protocol IP is the highest layer protocol which is implemented at both routers and hosts

  6. IP Service • Delivery service of IP is minimal • IP provide provides an unreliable connectionless best effort service (also called: “datagram service”). • Unreliable: IP does not make an attempt to recover lost packets • Connectionless: Each packet (“datagram”) is handled independently. IP is not aware that packets between hosts may be sent in a logical sequence • Best effort: IP does not make guarantees on the service (no throughput guarantee, no delay guarantee,…)

  7. IP • IP is connectionless in the end-to-end delivery • Data delivered in datagrams (packets / frames), each with a header • Combines collection of physical networks into single, virtual network • Transport protocols use this connectionless service to provide connectionless data delivery (UDP) and connection-oriented data delivery (TCP)

  8. IP is Best Effort Delivery • IP provides service equivalent to LAN • Does not guarantee to prevent • Duplicate datagrams • Delayed or out-of-order delivery • Corruption of data • Datagram loss • Reliable delivery provided by transport layer • Network layer - IP - can detect and report errors without actually fixing them

  9. IP Problems • Higher layer protocols have to deal with losses or with duplicate packets • Packets may be delivered out-of-sequence

  10. IP Service • IP supports the following services: • one-to-one (unicast) • one-to-all (broadcast) • one-to-several (multicast) • IP multicast also supports a many-to-many service. • IP multicast requires support of other protocols (IGMP, multicast routing) unicast broadcast multicast

  11. The IP Datagram • Formally, the unit of IP data delivery is called a datagram • Includes header area and data area • Datagrams can have different sizes • Header area usually fixed (20 octets) but can have options • Data area can contain between 1 octet and 65,535 octets (216- 1) • Usually, data area much larger than header

  12. Forwarding Datagrams • The header contains all the information needed to deliver a datagram to a destination computer • Destination address • Source address • Identifier • Other delivery information • Routers examine the header of each datagram and forwards the datagram along a path to the destination • Use routing table to compute next hop • Update routing tables using algorithms previously discussed • Link state, distance vector, manually

  13. IP Datagram Format • 20 bytes ≤Header Size< 24 x 4 bytes = 60 bytes • 20 bytes ≤Total Length< 216 bytes = 65536 bytes

  14. IP Datagram Format • Transmission is row by row • For each row: 1. First transmit bits 0-7 2. Then transmit bits 8-15 3. Then transmit bits 16-23 4. Then transmit bits 24-31 • Note: Many computers (incl. Intel processors) store 32-bit words in little endian format. Others (incl. Motorola processors) use big endian. • This iscallednetwork byte order (LE or BE) • "Big Endian" means that the high-order byte of the number is stored in memory at the lowest address, and the low-order byte at the highest address. • 0x1234: • BE: 12 34 LE: 34 12

  15. Maximum Transmission Unit • Maximum size of IP datagram is 65535, but the data link layer protocol generally imposes a limit that is much smaller • Example: • Ethernet frames have a maximum payload of 1500 bytes  IP datagrams encapsulated in Ethernet frame cannot be longer than 1500 bytes • The limit on the maximum IP datagram size, imposed by the data link protocol is called maximum transmission unit (MTU) • MTUs for various data link protocols: Ethernet: 1500 FDDI: 4352 802.3: 1492 ATM AAL5: 9180 802.5: 4464 PPP: negotiated

  16. Datagram Lifetime • Datagrams could loop indefinitely • Consumes resources • Transport protocol may need upper bound on datagram life • Datagram marked with lifetime • Time To Live field in IP • Once lifetime expires, datagram discarded (not forwarded) • Hop count • Decrement time to live on passing through a each router • Time count • Need to know how long since last router

  17. IP Fragmentation • What if the route contains networks with different MTUs? Or exceeds? • MTUs:FDDI: 4352Ethernet: 1500 • Fragmentation: • IP router splits the datagram into several datagram • Fragments are reassembled at receiver

  18. Where is Fragmentation done? • Fragmentation can be done at the sender or at intermediate routers • The same datagram can be fragmented several times. • Reassembly of original datagram is only done at destination hosts

  19. length =1500 length =4000 length =1040 length =1500 ID =x ID =x ID =x ID =x moreflag =0 moreflag =1 moreflag =0 moreflag =1 offset =0 offset =0 offset =1480 offset =2960 IP Fragmentation and Reassembly One large datagram becomes several smaller datagrams

  20. Fragmenting Fragments • A fragment may encounter a subsequent network with even smaller MTU • Router fragments the fragment to fit • Resulting (sub)fragments look just like original fragments (except for size) • No need to reassemble hierarchically; (sub)fragments include position in original datagram

  21. Dealing with Failure • Re-assembly may fail if some fragments get lost • Need to detect failure • Re-assembly time out • Assigned to first fragment to arrive • If timeout expires before all fragments arrive, discard partial data

  22. Error Control • Not guaranteed delivery • Router should attempt to inform source if packet discarded • e.g. for time to live expiring • Source may modify transmission strategy • May inform high layer protocol • Datagram identification needed • Destination doesn’t ACK or NAK if checksum fails, no retries, best-effort like Ethernet

More Related