TCP IP Illustrated

1 so it tries to forward the datagram to do this it

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Unformatted text preview: al UDP port numbers at 32768 by default, there is a much greater chance that the destination port is in use on the destination host. Chapter 9 9.1 When the ICMP standard was first specified, RFC 792 [Postel 1981b], subnetting was not in use. Also, using a single network redirect instead of N host redirects (for all N hosts on the destination network) saves some space in the routing table. 9.2 The entry is not required, but if it is removed, all IP datagrams to slip are sent to the default router (sun), which then forwards them to the router bsdi. Since sun is forwarding a datagram out the same interface on which it was received, it sends an ICMP redirect to svr4. This creates the same routing table entry on svr4 that we removed, although this time it is created by a redirect instead of being added at bootstrap time. 9.3 When the 4.2BSD host receives the datagram destined for 140.1.255.255 it finds that it has a route to the network (140.1) so it tries to forward the datagram. To do this it sends an ARP broadcast looking for 140.1.255.255. No reply is received for this ARP request, so the datagram is eventually discarded. If there are many of these 4.2BSD hosts on the file:///D|/Documents%20and%20Settings/bigini/Docu...homenet2run/tcpip/tcp-ip-illustrated/append_d.htm (6 of 20) [12/09/2001 14.48.03] Appendix D: Solutions to Selected Exercises cable, every one sends out this ARP broadcast at about the same time, swamping the network temporarily. 9.4 This time a reply is received for each ARP request, telling each 4.2BSD host to send the datagram to the specified hardware address (the Ethernet broadcast). If there are k of these 4.2BSD hosts on the cable, all receive their own ARP reply, causing each one to generate another broadcast. Each host receives each broadcast IP datagram destined to 140.1.255.255, and since every host now has an ARP cache entry, the datagram is forwarded again to the broadcast address. This continues and generates an Ethernet meltdown. [Manber 1990] describes other forms of chain reactions in networks. Chapter 10 10.1 Thirteen of the routes came from kpno: all except 140.252.101.0 and 140.252.1...
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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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