TCP IP Illustrated

TCP IP Illustrated

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Unformatted text preview: sing the sock program. Using the loopback interface under SunOS 4.1.3, the maximum size IP datagram was 32767 bytes. All higher values failed. But going across an Ethernet from BSD/386 to SunOS 4.1.3, the maximum size IP datagram the Sun could accept was 32786 (that is, 32758 bytes of user data). Using the loopback interface under Solaris 2.2, the maximum 65535-byte IP datagram could be sent and received. From Solaris 2.2 to AIX 3.2.2, the maximum 65535-byte IP datagram could be transferred. Obviously this limit depends on the source and destination implementations. We mentioned in Section 3.2 that a host is required to receive at least a 576-byte IP datagram. Many UDP applications are designed to restrict their application data to 512 bytes or less, to stay below this limit. We saw this in Section 10.4, for example, where the Routing Information Protocol always sent less than 512 bytes of data per datagram. We'll encounter this same limit with other UDP applications: the DNS (Chapter 14), TFTP (Chapter 15), BOOTP (Chapter 16), and SNMP (Chapter 25). Datagram Truncation Just because IP is capable of sending and receiving a datagram of a given size doesn't mean the receiving application is prepared to read that size. UDP programming interfaces allow the application to specify the maximum number of bytes to return each time. What happens if the received datagram exceeds the size the application is prepared to deal with? Unfortunately the answer depends on the programming interface and the implementation. The traditional Berkeley version of the sockets API truncates the datagram, discarding any excess data. Whether the application is notified depends on the version. (4.3BSD Reno and later can notify the application that the datagram was truncated.) file:///D|/Documents%20and%20Settings/bigini/Doc...omenet2run/tcpip/tcp-ip-illustrated/udp_user.htm (19 of 29) [12/09/2001 14.46.58] Chapter 11. UDP: User Datagram Protocol The sockets API under SVR4 (including Solaris 2.x) does not truncate the datagram. Any excess data is returned in su...
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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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