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Internet Protocol

Internet Protocol. 2005. 3. 16 백 일 우. Basic Features. Unreliable, connectionless Delivery Best Effort Service No Guarantee that IP datagram successfully get to its Dest. When Something wrong, IP runs A simple error Handling Algorithm ICMP : Congestion, Redirect, Packet Arrived or Not

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Internet Protocol

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  1. Internet Protocol 2005. 3. 16 백 일 우

  2. Basic Features • Unreliable, connectionless Delivery • Best Effort Service • No Guarantee that IP datagram successfully get to its Dest. • When Something wrong, IP runs A simple error Handling Algorithm • ICMP : Congestion, Redirect, Packet Arrived or Not • Each Datagram is Handled Independently, so Delivered out of order • Fragmentation/Reassembly For supporting network Interface which has variable frame sizes

  3. IP Header • Version • Only V4 and V6 are used • Other is not used

  4. IP Header • Header Length • Range is 4bits, so it can present values 0~15 • Specifies the length of the IP packet header in 32 bit words • Header Length = Real Value Times(*) 4byte(32bits) • If value is 5, Real Length is 5*4 = 20 (bytes) • Header Length valid Range • 5 ~ 15 • Minimun 20 ~ Maximum 60 (5*4 ~ 15*4) • It is only can be presented by a multiple of 4 • So, If Can not be presented by 4-multiple, Must add ‘Padding’ to be type of 4-multiple

  5. IP Header • Type of Service (TOS) • Specifies the parameters for the type of service requested • The parameters may be utilized by networks to define the handling of the datagram during transport • Precedence • Basically Setted by 000, the others is not allowed • Delay • 0 : Normal Delay, 1: Low Delay • 1 for sound, movie and Logon request • Throughput • 0 : normal Throughput, 1: High throughput • If 1, a Router select the way which has the best BW

  6. IP Header • Precedence

  7. IP Header • Reliability • 0 : normal Reliability, 1: High Reliability • As so many traffics are driven to some router, the router decide which packet is less significant with Reliability Field, and Drop it. • Cost • 0 : normal Cost, 1 : Low Cost • Decide which way is more reasonable, checking this field. • Reserved • Last field is always set by 0 (MBZ : Must Be Zero), So routers ignore this field. • Total Length • Contains the length of the datagram (16 bits) – MAX : 65535 bytes • IP header + IP Payload • MAX(65535 bytes) possible, but most link-Layer will fragment this

  8. IP Header • Identification (16bits) • Used to identify the fragments of one datagram from those of another. • Flags • R, Reserved. 1 bit. Should be cleared to 0. • DF, Don’t Fragment, 1bit. • Controls the fragmentation of the datagram • 0 : Fragment if necessary, 1 : Nope! Fragment • MF,More fragments. 1 bit. • Indicates if the datagram contains additional fragments • 0 : This is the last Fragment, 1: More Fragments follows after this • Fragment Offset (13 bits) • Used to direct the reassembly of a fragmented datagram

  9. 001 123 0000 123 2,300 bytes IP Header – Fragmentation More Fragments follow <Identification & Fragmentation> Identification 1000 001 123 Last Fragment 2000 000 123 MTU = 2,300 MTU = 1,000 ROUTER <Fragment Offet 역할> B C D A IP Header IP Header PayLoad A까지 IP Header PayLoad B까지 IP Header PayLoad C까지 IP Header PayLoad D까지

  10. IP Header H7 R3 H8 H1 H2 H3 Network 4 (Point-to-Point) Network 2(Ethernet) Network 2(Ethernet) R1 R2 Ethernet MTU : 1500 FDDII MTU : 4500 Suppose PtoP MTU is 532(included Header) H1 datagram : 1420 H4 Network 3(FDDI) H5

  11. Start of header Start of header Start of header Start of header Iden = A Iden = A Iden = A Iden = A 1 0 1 0 Offset = 0 Offset = 0 Offset = 1024 Offset = 512 Rest of Header Rest of Header Rest of Header Rest of Header 512 data bytes 376 data bytes 1400 data bytes 512 data bytes IP Header • 1400 bytes split into pieces of 512 bytes > 1400 = 512 + 512 + 376

  12. IP Header • TTL (Time To live) – 8bits • A timer field used to track the lifetime of the datagram. When the TTL field is decremented down to zero, the datagram is discarded • Protocol – 8bits • This field specifies the next encapsulated protocol

  13. IP Routing - Intro • Forwarding • That is, Send the packet which is sent from outside to reasonable path, checking the routing table • Routing • That is, Configuring the routing table to make the router send the packet to the reasonable path • Routing Table Contains.., • Destination IP addr • This can be either a complete host addr, or a network addr, as specified by the flag field • IP addr of a next-hop router • Flags • One specifies whether Dest IP addr is Addr of Network or Host • Another says whether the next-hop router field is really a next-hop router or a directly connected interface.

  14. IP Routing - Intro Minimal Encapsulation

  15. IP Routing - Intro • Key Points from previous examples • All hosts and routers in this example used a default route. Indeed, most host and some routers can use a default route for everything other than destinations on Local networks • The Destination IP addr in the datagram never changes. All the routing decision are based on this destination address • In previous Example, Both Ethernets encapsulated header containing the next-hop’s ethernet address, but the SLIP link did NOT • The Ethernet addresses are normally obtained using ARP

  16. Subnetting & Subnet Mask • Purpose • For efficient IP address usage, and Reducing the size of routing tables • Subnet • One network Number of IPs can be assigned in many physical Networks • Conditions • Seen from outside as if It were single Network • That is, Router can select one path for them • Campus can be good example • All nodes on each subnet must be configured with same subnet mask to share Just one network number • Subnet Mask • IP organization Could be more specific • Network and host to Network, subnet, and host

  17. Network Number Host Number Class B 111111111111111111111 00000000 Subnet mask(255.255.255.0) Network Number Subnet ID Host ID Subnetted Address Subnetting & Subnet Mask Subnet Mask : 255.255.255.128 Subnet Number : 128.96.34.0 128.96.34.15 128.96.34.1 H1 R1 • H1 -> H2로 보내고자 한다면, • And 연산을 한다 • 결과 : 128.96.34.128 • H1의 서브넷과 일치 않함!! • H1과 H2는 다른 서브넷상에 있다는 것을 알수 있음 128.96.34.130 Subnet Mask : 255.255.255.128 Subnet Number : 128.96.34. 128 128.96.34.139 H3 R2 H2 128.96.33.1 128.96.33.14

  18. Subnetting & Subnet Mask • H1 -> H2 • R1: 128.96.34.139 AND 255.255.255.128 • Result : 128.96.34.128 • Compare 128.96.34.0 with 128.96.34.128 -> X • Compare 128.96.34.0 with next entry • Through this works, R1 forward to H2 using interface 1 <Subnetted Forwarding Table>

  19. Question • 패킷 단편화후 그 단편화된 Datagram들이 꼭 순서에 맞게 도착하지 않음 . • Host에서는 맨 마지막 조각이 오고 나서 재조립을 시작하는가. • Flag M = 0 이라는 마지막 조각이 먼저 오게 되면, 언제까지 기다려야 되나.

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