1. TCP/IP Illustrated Volume I Internet Protocol 2005. 3. 16 백 일 우

2. 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 Network TypeIP MTU (BYTE) Ethernet(Ethernet II)1500 Ethernet(802.3)1492 Token Ring(802.5) 4440 – 17940(Token Ring 의 Holding Time 에 따라 다름 ) FDD I1600 Frame Relay4352 Minimun MTU576

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

4. 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. 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. 6 IP Header Precedence Precedence ValuePrecedence 000Routine 001Priority 010Immediate 011Flash 100Flash Override 101CRITIC/ECP 110Internetwork Control 111Network Control

7. 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. 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. 9 IP Header – Fragmentation MTU = 1,000MTU = 2,300 2,300 bytes 123 ROUTER 0000 001123 2000 000123 1000 001123 More Fragments follow Last Fragment Identification IP Header PayLoad IP HeaderPayLoad IP HeaderPayLoad IP HeaderPayLoad A BCD A 까지 B 까지 C 까지 D 까지

10. 10 IP Header Network 3(FDDI) H1H2H3 H7R3H8 H4 H5 R1R2 Network 2(Ethernet) Network 4 (Point-to-Point) 1. Ethernet MTU : 1500 2. FDDII MTU : 4500 3. Suppose PtoP MTU is 532(included Header) 4. H1 datagram : 1420

11. 11 IP Header 1400 bytes split into pieces of 512 bytes Start of header Iden = A1Offset = 0 Rest of Header 512 data bytes Start of header Iden = A1Offset = 512 Rest of Header 512 data bytes Start of header Iden = A0Offset = 1024 Rest of Header 376 data bytes Start of header Iden = A0Offset = 0 Rest of Header 1400 data bytes > 1400 = 512 + 512 + 376

12. 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. 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. 14 IP Routing - Intro Minimal Encapsulation

15. 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. 16 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 Subnetting & Subnet Mask

17. 17 Subnetting & Subnet Mask Network NumberHost Number 11111111111111111111100000000 Network NumberSubnet IDHost ID Class B Subnet mask(255.255.255.0) Subnetted Address H3 R2H2 R1 H1 Subnet Mask : 255.255.255.128 Subnet Number : 128.96.34.0 Subnet Mask : 255.255.255.128 Subnet Number : 128.96.34. 128 128.96.34.139 128.96.33.1 128.96.33.14 128.96.34.1 128.96.34.130 128.96.34.15 1. H1 -> H2 로 보내고자 한다면, 2. And 연산을 한다 1. 결과 : 128.96.34.128 3. H1 의 서브넷과 일치 않함 !! 1. H1 과 H2 는 다른 서브넷상에 있다는 것을 알수 있음

18. 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 Subnet NumberSubnet MaskNext Hop 128.96.34.0255.255.255.128Interface 0 128.96.34.128255.255.255.128Interface 1 128.96.33.0255.255.255.0R2

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