IPv4 (Part III) รศ.ดร. อน นต ผลเพ ม Asso. Prof. Anan Phonphoem, Ph.D. Nov 2010

Transcription

1 Nov 2010 IPv4 (Part III) รศ.ดร. อน นต ผลเพ ม Asso. Prof. Anan Phonphoem, Ph.D. Computer Engineering Department Kasetsart University, Bangkok, Thailand 1

2 Outline IP Fundamental Operation Internet Protocol Addressing Supporting Protocol ARP ICMP: ping + traceroute NAT DHCP 2

3 Internet Control Message Protocol (ICMP) 3

4 ICMP IP supporter For error generating Transmission problem TTL exceed Destination unreachable etc. Serve as useful diagnostics ping, traceroute 4

5 ICMP ICMP error messages never generates due to: ICMP error messages selves Broadcast/Multicast (prevent broadcast Storms) What are Broadcast Storms? A large number of broadcast datalink frames transmitted nearly simultaneous LAN may be freeze! 5

6 Positioning of ICMP 6

7 ICMP encapsulation Type: 0x0806 Preamble and SFD Destination address Frame Header Source address Type Data CRC 8 bytes 6 bytes 6 bytes 2 bytes 4 bytes 7

8 ICMP packet DA IP SA T Type Code Other info. header Frame (Ethernet) Header IP Header ICMP Type Code Description 8 0 Echo request 0 0 Echo reply 11 0 Time exceed 3 3 Port unreachable 8

9 ICMP header type - relevant ICMP message code - more detail information checksum - covers ICMP header/data (not IP hdr) type:8 code:8 checksum:16 Content specific 9

10 ping ping request ping reply Generate an ICMP echo request Receive the ICMP echo reply All TCP/IP node is supposed to implement ICMP and respond to ICMP echo 10

11 ping command Send an echo request message every seconds Records the time it takes for each reply Every echo request contains a unique sequence number to match replies and request Record round-trip timing Perform packet lost statistics 11

12 ping example anan]$ ping iwing.cpe.ku.ac.th PING iwing.cpe.ku.ac.th ( ) from : 56(84) bytes of data. Warning: time of day goes back, taking countermeasures. 64 bytes from iwing.cpe.ku.ac.th ( ): icmp_seq=0 ttl=252 time=1.187 msec 64 bytes from iwing.cpe.ku.ac.th ( ): icmp_seq=1 ttl=252 time=601 usec 64 bytes from iwing.cpe.ku.ac.th ( ): icmp_seq=2 ttl=252 time=594 usec 64 bytes from iwing.cpe.ku.ac.th ( ): icmp_seq=3 ttl=252 time=594 usec 64 bytes from iwing.cpe.ku.ac.th ( ): icmp_seq=4 ttl=252 time=585 usec 64 bytes from iwing.cpe.ku.ac.th ( ): icmp_seq=5 ttl=252 time=590 usec 64 bytes from iwing.cpe.ku.ac.th ( ): icmp_seq=6 ttl=252 time=584 usec 64 bytes from iwing.cpe.ku.ac.th ( ): icmp_seq=7 ttl=252 time=587 usec --- iwing.cpe.ku.ac.th ping statistics packets transmitted, 8 packets received, 0% packet loss round-trip min/avg/max/mdev = 0.584/0.665/1.187/0.198 ms 12

13 ping as debugging tools What do we get from ping? Timing information Connection reliability Destination is reachable (routable) Layer is functional, but not guaranteed telnet! 13

14 ping results no response no end node, no connection lost packet (significant when >2-3%) transmission error on WAN/LAN, overloading bridges/routers time acknowledge vary host/network overloading, >100 ms make telnet less acceptable) no lost and echo time is reasonably constant Congratulation! That s all we want. 14

15 traceroute Command to determine the active route to a destination address How to? send a UDP messages to an unused port on the target host with ttl=1 router decrease ttl to 0, it has to return an ICMP time exceed message traceroute sets ttl =2 and retransmits, this time go one more hop ttl++ until UDP messages reach the destination. the target returns an ICMP service unavailable because there is no UDP port service. 15

16 How traceroute works? UDP(TTL =1) Destination unused port # 16

17 How traceroute works? UDP(TTL = 0=1) ICMP(time UDP(TTL =1) exceed) 17

18 How traceroute works? UDP(TTL ICMP(time = 0=1) exceed) UDP(TTL ICMP(time =1) =2) exceed) UDP(TTL ICMP(time =2) exceed) 18

19 How traceroute works? UDP(TTL =8) UDP(TTL =9) ICMP(port UDP(TTL =10) unreachable) ICMP(port UDP(TTL unreachable) =0) Various of traceroute: TCP sync (not common) 19

20 Traceroute example anan]$ /usr/sbin/traceroute iwing.cpe.ku.ac.th traceroute to iwing.cpe.ku.ac.th ( ), 30 hops max, 38 byte packets 1 fe-cpegw2-server ( ) ms ms ms 2 gb-cpegwbb-cpegw ( ) ms ms ms 3 gb-cpec4k6-cpec6k ( ) ms ms ms 4 iwing ( ) ms ms ms 20

21 Traceroute example anan]$ /usr/sbin/traceroute traceroute to ( ), 30 hops max, 38 byte packets 1 fe-cpegw2-server ( ) ms ms ms 2 gb-cpegwbb-cpegw ( ) ms ms ms ( ) ms ms ms ( ) ms ms ms ( ) ms ms ms ( ) ms ms ms ( ) ms ms ms ( ) ms ms ms 9 S1-1.R00.LA-POP.uni.net.th ( ) ms ms ms ( ) ms ms ms 11 snvang-losang.abilene.ucaid.edu ( ) ms ms ms 12 dnvrng-snvang.abilene.ucaid.edu ( ) ms ms * 13 kscyng-dnvrng.abilene.ucaid.edu ( ) ms ms ms 19 nox300gw1-peer-nox-umass nox.org ( ) ms ms ms 20 lgrc-rt gw.umass.edu ( ) ms ms ms 21 lgrc-rt gw.umass.edu ( ) ms ms ms 22 * * * 23 * * * 21

22 Example GUI Traceroute program: Visual Route 22

23 Example GUI Traceroute program: Visual Route 23

24 Assignment Select 2 URLs from any site in the world Not the same continent On different times (e.g. 9AM, 3PM, 11PM) of the day ping traceroute (from your machine) Create an example graphical route for each URL a comparison table for different times / sites Summarize and criticize the results 24

25 Ping Example Ping Time results Average (ms) % loss 9AM [ ] with 32 bytes of data: Reply from : bytes=32 time=322ms TTL=127 Reply from : bytes=32 time=506ms TTL=127 Reply from : bytes=32 time=502ms TTL=127 Reply from : bytes=32 time=325ms TTL= PM 11PM 25

26 Outline IP Fundamental Operation Internet Protocol Addressing Supporting Protocol ARP ICMP: ping + traceroute NAT DHCP 26

27 Network Address Translation (NAT) 27

28 Network Address Translation (NAT) Private Network Good practice to use private address Map local addresses to (real) public IP address(es) Security (not expose internal details) Alleviate IP depletion 28

29 Private IP address Class RFC 1918 CIDR prefix A /8 B /12 C /16 29

30 NAT Operates at the border of a stub network 30

31 NAT 31

32 ADSL Connection ADSL Modem Telephone Line ISP Internet ADSL Router ADSL Modem ADSL Modem WLAN ADSL Router 32

33 Configure NAT Static Translation Dynamic Translation 33

34 Static Translation 34

35 Example Source: Source: Internet Site using private addresses Destination: Destination:

36 Dynamic Translation 36

37 PAT: Port Address Translation (Overloaded NAT) 37

38 PAT

39 Disadvantages of NAT Delay Loss of end-to-end ability Might not work with some applications 39

40 Bootstrap Protocol (BOOTP) 40

41 BOOTP Diskless terminal Discover its own IP address Download executable image file Small program built in chip BOOTH and TFTP Application Protocol Encapsulated in IP and UDP 41

42 BOOTP packet format 42

43 Operation 43

44 Dynamic Host Configuration Protocol (DHCP) 44

45 DHCP BOOTP Enhancement Same message structure as BOOTP Can choose among many DHCP servers 45

46 DHCP packet 46

47 Operation 47

48 DHCP Message 48

49 DHCP transition diagram 49

50 DHCP Relay 50

51 DHCP Relay 51

52 Summary IP Fundamental Operation Internet Protocol Addressing Supporting Protocol ARP ICMP: ping + traceroute NAT DHCP 52