TCP IP Illustrated

2521365 bsdi 1402521335

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Unformatted text preview: 0.252.13.35) file:///D|/Documents%20and%20Settings/bigini/Docu...homenet2run/tcpip/tcp-ip-illustrated/pingprog.htm (8 of 13) [12/09/2001 14.46.45] Chapter 7. Ping Program svr4 (140.252.13.34) 64 bytes from 140.252.13.65: icmp_seq=1 ttl=254 time=280 ms (same route) 64 bytes from 140.252.13.65: icmp_seq=2 ttl=254 time=270 ms (same route) ^? --- slip ping statistics --3 packets transmitted, 3 packets received, 0% packet loss round-trip min/avg/max = 270/276/280 ms Figure 7.4 shows the four hops that the packets take (two in each direction), and which hop adds which IP address to the RR list. Figure 7.4 ping with record route option. The router bsdi adds a different IP address to the list in each direction. It always adds the IP address of the outgoing interface. We can also see that when the ICMP echo reply reaches the originating system (svr4) it adds the IP address of the incoming interface to the list. We can also watch this exchange of packets from the host sun, running tcpdump with its -v option (to see the IP options). Figure 7.5 shows the output. 1 0.0 2 0.267746 (0.2677) svr4 > slip: icmp: echo request (ttl 32, id 35835, optlen=40 RR{39}=RR(#0.0.0.0/0.0.0.0/0.0.0.0/ 0.0.0.0/0.0.0.0/0.0.0.0/0.0.0.0/0.0.0.0/0.0.0.0} EOL) slip > svr4: icmp: echo reply (ttl 254, id 1976, optlen=40 RR{39}= RR(140.252.13.66/140.252.13.65/ 140.252.13.35/#0.0.0.0/0.0.0.0/0.0.0.0/0.0.0.0/ 0.0.0.0/0.0.0.0} EOL) Figure 7.5 tcpdump output of record route option. The output optlen=40 indicates there are 40 bytes of option space in the IP header. (Recall that the length of the IP header must be a multiple of 4 bytes.) RR{39} means the record route option is present, and its length field is 39. The list of nine IP addresses is then shown, with a file:///D|/Documents%20and%20Settings/bigini/Docu...homenet2run/tcpip/tcp-ip-illustrated/pingprog.htm (9 of 13) [12/09/2001 14.46.45] Chapter 7. Ping Program pound sign (#) indicating which IP address is pointed to by the ptr field in the RR option header. Since we are watching the...
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This test prep was uploaded on 04/04/2014 for the course ECE EL5373 taught by Professor Guoyang during the Spring '12 term at NYU Poly.

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