TCP IP Illustrated

We used udp to examine this checksum and to see how

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Unformatted text preview: int gets the unicast datagram is implementation dependent. 11.13 Summary UDP is a simple protocol. Its official specification, RFC 768 [Postel 1980], requires only three pages. The services it provides to a user process, above and beyond IP, are port numbers and an optional checksum. We used UDP to examine this checksum and to see how fragmentation is performed. We then examined the ICMP unreachable error that is part of the new path MTU discovery feature (Section 2.9). We watched path MTU discovery using Traceroute and UDP We also looked at the interaction between UDP and ARP whereby most ARP implementations only retain the most recently transmitted datagram to a given destination, while waiting for an ARP reply. The ICMP source quench error can be sent by a system that is receiving IP datagrams faster than they can be processed. It is easy to generate these ICMP errors using UDP. Exercises 11.1 In Section 11.5 we caused fragmentation on an Ethernet by writing a UDP datagram with 1473 bytes of user data. What is the smallest amount of user data that causes fragmentation on an Ethernet if IEEE 802 encapsulation (Section 2.2) is used instead? 11.2 Read RFC 791 [Postel 1981a] to determine why all fragments other than the last must have a length that is a multiple of 8 bytes. 11.3 Assume an Ethernet and a UDP datagram with 8192 bytes of user data. How many fragments are transmitted and what is the offset and length of each fragment? file:///D|/Documents%20and%20Settings/bigini/Doc...omenet2run/tcpip/tcp-ip-illustrated/udp_user.htm (28 of 29) [12/09/2001 14.46.58] Chapter 11. UDP: User Datagram Protocol 11.4 Continue the previous exercise, assuming these fragments then traverse a SLIP link with an MTU of 552. You also need to remember that the amount of data in each fragment (i.e., everything other than the IP header) must be a multiple of 8 bytes. How many fragments are transmitted and what is the offset and length of each fragment? 11.5 An application using UDP sends a datagram that...
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