Vaasan Yliopisto 2006

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Vaasan Yliopisto 2006

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1. IP Vaasan Yliopisto 2006

2. IP in TCP/IP Internet protocol is TCP/IP protocol family’s transfer system In TCP/IP network Internet protocol encapsulates every protocol with its own PDU except ARP

3. Internet Addresses Internet address is IP address that is assigned to interface card Computer can have many addresses 32-bit IP address encodes network ID and host ID InterNIC defines network Ids (Internet Network Information Centre) Network administrator defines host IDs

4. Addresses are usually expressed with four dot separated decimal numbers Each number represent one byte E.g.: 10000110 00011000 00001000 01000010 = 2 249 721 922 = 0x86180842 =

5. Address Classes 5 Classes

6. Class A address is used by those rare networks that must connect over 65 534 computers (max. 16 777 215 pc.)

7. Class B addresses are used in networks that have over 254 computers (max. 65534)

8. Class C addresses can be used to separate 2 097 152 network, max. 254 computers/network

9. IP addresses are divided to 1) unicast 2) broadcast 3) multicast addresses Class A, B and C addresses are unicast addresses Class D is reserved to multicast addresses Class E is reserved for later use

10. IPv4 has 32 bits for address => 4 billion addresses (expected to run out 2005-2015) IPv6 has 128 bit addresses => many thousands of addresses for each square meter in Earth (IPv5??)

11. IPV6 Resource reservation, security (user identification, data authenticity, confidentiality), data flow, priorities Packet constructs from address header (40 bytes) and optional extension headers Node options (e.g. drop packet if changed in transfer) Routing Fragmentation (smallest MTU from end to end) Destination options (checked only in destination)

12. Internet Address Protocols ARP (Address Resolution Protocol) ARP module maps internet layer addresses (IP addresses) to corresponding network interface layer addresses (e.g. Ethernet addresses) ARP is dynamic in respect of network configuration RARP (Reverse Address Resolution Protocol) Reverse mapping Gets IP address from server

13. IP packet TCP/IP network encapsulates almost all information in Internet to IP packet Encapsulation creates datagram that has IP header and data Headers length is multiple of 32 bits, usually 20 bytes Header includes all information that is needed to transfer data in IP packet

15. Version number (VERS, 4 bits) What version of IP protocol is used Header length (HLEN, 4 bits) IP header length in 32 bit words e.g. header length 20 bytes field set to 5 Encapsulated data begins directly after header

16. Type of service (TOS, 8 bits) Defines priority of IP packet Network layer can use these when handling packets 5 subfields: precedence, delay, throughput, reliability, cost Precedence field (value 0-7) defines general priority of data, other fields are application specific priorities

17. Total length (16 bits) Length of whole IP packet in bytes Maximum length is 64 kB Identification (16 bits) Identifies uniquely every packet host sends

18. Flags (3 bits) When 1st bit is set, IP packet cannot be fragmented When 3rd bit is set, more fragments follow this fragment Fragment offset (13 bits) Fragments offset in IP packet, multiple of 8 bytes from beginning of packet

19. Time-to-Live (TTL, 8 bits) Every node between source and destination subtracts one from value Initial value (usually between 30-255) defines max hop number Is value reduces to zero, packet is dropped and source is informed Protocol (8 bits) Defines what protocol created data that is encapsulated in packet (i.e. what transport module network layer must connect)

20. Header checksum (16 bits) Although IP unreliable protocol, it uses checksum to detect errors Checksum corresponds only to IP header If receiving computer detects error, packet is dropped Receiving computer does not inform sender

21. Source and destination IP addresses (32 bits) IP options (8 bits) Used when testing network applications Control fragmentation and routing of packets and information logging while routing

22. Fragmenting Fragmenting is process where one packet is divided to many smaller ones, fragments Used network technology defines maximum size of transferred packet (MTU, Maximum Transfer Unit) e.g. Ethernet MTU 1500 bytes

23. Sending computer divides IP packet bigger than MTU to smaller fragments Fragments include information needed to reassemble packet Fragment size is as close to MTU as possible, but it has to be multiple of 8 bytes If “don’t fragment” flag is set, too big packet is dropped

24. Receiving computer assembles fragments using source address, identification, flags and fragment offset fields Source address defines sender of fragment Identification field defines to what packet fragments belong Flags field informs if this is last fragment Fragment offset defines fragments position in packet

25. When destination computer receives packet that has “more fragments” flag set, it starts fragment timer All fragments must arrive before times stops If fragmenting is used, probability that data does not reach destination increases

26. Avoiding Fragmentation TCP uses 576 byte default MTU when it transfers data to host across many routers This value gives 512 bytes to data and leaves space for TCP and IP headers and header options Most of data link layer protocols support 576 byte MTU and do not fragment packets TCP/IP application type can be used to analyze different routing possibilities Possibly can use bigger packet size

27. Routing When sender and receiver are in same network, sender gets receivers network address using ARP and sends packet directly to receiver Sender gets receivers network ID from IP address using subnet mask and compares to its own subnet mask Otherwise sender transmits packet to local router Router is found using routing table

28. IP routing table contains addresses of defined network destinations Routing protocols take care of information in routing table Every row in routing table contains 3 fields: Network = destination network ID Gateway = Id to router that is on route to destination Flags = set when destination network is connected directly to routing table owner

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