TCP IP Illustrated

This can lead to timeouts for resolver queries that

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Unformatted text preview: ecedes the actual DNS message. 14.5 When a name server starts it normally reads the (possibly out of date) list of root servers from a disk file. It then tries to contact one of these root servers, requesting the name server records (a query type of NS) for the root domain. This returns the current upto-date list of root servers. Minimally this requires one of the root server entries in the file:///D|/Documents%20and%20Settings/bigini/Docu...homenet2run/tcpip/tcp-ip-illustrated/append_d.htm (9 of 20) [12/09/2001 14.48.04] Appendix D: Solutions to Selected Exercises start-up disk file to be current. 14.6 The registration services of the InterNIC updates the root servers three times a week. 14.7 Since the resolver comes and goes, as applications come and go, if the system is configured to use multiple name servers and the resolver maintains no state, the resolver cannot keep track of the round-trip times to its various name servers. This can lead to timeouts for resolver queries that are too short, causing unnecessary retransmissions. 14.8 Sorting the A records should be done by the resolver, not the name server, since the resolver normally knows more than the server about the network topology of the client. (Newer releases of BIND provide for resolver sorting of A records.) Chapter 15 15.1 TFTP requests sent to the broadcast address should be ignored. As stated in the Host Requirements RFC, responding to a broadcast request can create a significant security hole. A problem, however, is that not all implementations and APIs provide the destination address of a UDP datagram to the process that receives the datagram (Section 11.12). For this reason many TFTP servers don't enforce this restriction. 15.2 Unfortunately, the RFC says nothing about this block number wrap. Implementations should be able to transfer files up through 33,553,920 bytes (65535 x 512). Many implementations fail when the size of the file exceeds 16,776,704 (32767 x 512) since they incorrectly maintain the block number as a signed 16-bit integer instead of an unsigned integer. 15.3 This simplifies coding a TFTP client to fit in read-only memory, because the server is the sender...
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