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Unformatted text preview: cmp_seq=0 ttl=254 time=280 ms (DUP!)
64 bytes from 184.108.40.206; icmp_seq=0 ttl=254 time=360 ms
64 bytes from 220.127.116.11; icmp_seq=l ttl=255 time=180 ms
64 bytes from 18.104.22.168: icmp_seq=l ttl=254 time=270 ms
64 bytes from 22.214.171.124: icmp_seq=l ttl=254 time=360 ms
^? type interrupt key to stop
- 126.96.36.199 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 vangogh.cs.berkeley.edu (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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- Spring '12