TCP IP Illustrated

type interrupt key to stop 1402521363 ping statistics

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Unformatted text preview: cmp_seq=0 ttl=254 time=280 ms (DUP!) 64 bytes from; icmp_seq=0 ttl=254 time=360 ms (DUP!) 64 bytes from; icmp_seq=l ttl=255 time=180 ms 64 bytes from icmp_seq=l ttl=254 time=270 ms (DUP!) 64 bytes from icmp_seq=l ttl=254 time=360 ms (DUP!) ^? type interrupt key to stop - ping statistics - file:///D|/Documents%20and%20Settings/bigini/Docu...homenet2run/tcpip/tcp-ip-illustrated/broadcas.htm (7 of 12) [12/09/2001 14.47.00] Chapter 12. Broadcasting and Multicasting 3 packets transmitted, 2 packets received, +4 duplicates, 33% packet loss round-trip min/avg/max = 180/273/360 ms We see that this does indeed work. We also see that the BSD ping program checks for duplicate sequence numbers and prints DUP! when this occurs. It normally means a packet was duplicated somewhere, but here we expect to see this, since we sent the requests to a broadcast address. We can also run this test from a host much farther away from the network to which the broadcast is directed. If we run ping from the host (14 hops away from our network), it still works if the router sun is configured to forward directed broadcasts. In this case the IP datagrams (carrying the ICMP echo requests) are forwarded by every router in the path as a normal datagram. None of them knows that it's really a directed broadcast. The next to last router, netb, thinks it's for the host with an ID of 63, and forwards it to sun. It is the router sun that detects that the destination IP address is really the broadcast address of an attached interface, and turns the datagram into a link-layer broadcast on that network. Broadcasting is a feature that should be used with great care. In many cases IP multicasting will prove to be a better solution. 12.4 Multicasting IP multicasting provides two services for an application. 1. Delivery to multiple destinations. There are many applications that deliver information to multiple recipients: interactive confer...
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