TCP IP Illustrated

Htm 5 of 7 12092001 144702 chapter 13 igmp internet

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Unformatted text preview: d. We have shown the hardware addresses in these two lines, to verify that the Ethernet destination address is the correct multicast address. We can also see that the source IP address is the one corresponding to sun, and file:///D|/Documents%20and%20Settings/bigini/Docum.../homenet2run/tcpip/tcp-ip-illustrated/igmp_int.htm (5 of 7) [12/09/2001 14.47.02] Chapter 13. IGMP: Internet Group Management Protocol the destination IP address is the multicast group address. We can also see that the reported address is that same multicast group address. Finally, we note that the TTL is 1, as specified, tcpdump prints the TTL in square brackets when its value is 0 or 1. This is because the TTL is normally greater than this. With multicasting, however, we expect to see lots of IP datagrams with a TTL of 1. Implied in this output is that a multicast router must receive all multicast datagrams on all its interfaces. The router has no idea which multicast groups the hosts might join. Multicast Router Example Let's continue the previous example, but we'll also start a multicast routing daemon on the host sun. Our interest here is not the details of multicast routing protocols, but to see the IGMP queries and reports that are exchanged. Even though the multicast routing daemon is running on the only host that supports multicasting (sun), all the queries and reports are multicast on the Ethernet, so we can see them on any other system on the Ethernet. Before starting the routing daemon we joined another multicast group: 224.9.9.9. Figure 13.5 shows the output. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0.0 0.00 ( 0.00) 5.10 ( 5.10) 5.22 ( 0.12) 7.90 ( 2.68) 8.50 ( 0.60) 11.70 ( 3.20) 125.51 (113.81) 125.70 ( 0.19) 128.50 ( 2.80) 129.10 ( 0.60) 247.82 (118.72) 248.09 ( 0.27) 248.69 ( 0.60) 255.29 ( 6.60) sun sun sun sun sun sun sun sun sun sun sun sun sun sun sun > > > > > > > > > > > > > > > 224.0.0.4: 224.0.0.1: 224.9.9.9: 224.0.0.1: 224.1.2.3: 22...
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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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