TCP IP Illustrated


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Unformatted text preview: ion Protocol 1 2 3 4 5 0:0:c0:6f:2d:40 ff:ff:ff:ff:ff:ff arp 60: arp who-has svr4 tell bsdi 0.002174 0:0:c0:c2:9b:26 0:0:c0:6f:2d:40 arp 60: (0.0022) arp reply svr4 is-at 0:0:c0:c2:9b:26 0:0:c0:6f:2d:40 0:0:c0:c2:9b:26 ip 60: 0.002831 bsdi.1030 > svr4.discard: S (0.0007) 596459521:596459521(0) win 4096 <mss 1024> [tos 0x10] 0:0:c0:c2:9b:26 0:0:c0:6f:2d:40 ip 60: 0.007834 svr4.discard > bsdi.1030: S (0.0050) 3562228225:3562228225(0) ack 596459522 win 4096 <mss 1024> 0:0:c0:6f:2d:40 0:0:c0:c2:9b:26 ip 60: 0.009615 bsdi.1030 > svr4.discard: . ack 1 win 4096 (0.0018) [tos 0x10] Figure 4.4 ARP request and ARP reply generated by TCP connection request. 0.0 Figure A.3 in Appendix A contains the raw output from tcpdump used for Figure 4.4. Since this is the first example of tcpdump output in the text, you should review that appendix to see how we've beautified the output. We have deleted the final four lines of the tcpdump output that correspond to the termination of the connection (which we cover in Chapter 18), since they're not relevant to the discussion here. In line 1 the hardware address of the source (bsdi) is 0:0:c0:6f:2d:40. The destination hardware address is ff:ff:ff:ff:ff:ff, which is the Ethernet broadcast address. Every Ethernet interface on the cable will receive the frame and process it, as shown in Figure 4.2. The next output field on line 1, arp, means the frame type field is 0x0806, specifying either an ARP request or an ARP reply. The value 60 printed after the words arp and ip on each of the five lines is the length of the Ethernet frame. Since the size of an ARP request and ARP reply is 42 bytes (28 bytes for the ARP message, 14 bytes for the Ethernet header), each frame has been padded to the Ethernet minimum: 60 bytes. Referring to Figure 1.7, this minimum of 60 bytes starts with and includes the 14-byte Ethernet header, but does not include the 4-byte Ethernet trailer. Some books state the minimum as 64 bytes, which includes the Ethernet trailer. We purposely did not include the 14-byte Ethernet header in the minimum o...
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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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