Chapter 6

p. 71

Information request/reply have been superseded by BOOTP (Chapter 16) or DHCP as means of configuring discless machines. RFC 1700 (and the updating files) lists several other possible ICMP types, but these are not in widespread use.

p. 79

The statement in figure 6.10, that the error message should contain the first eight bytes of the IP data, has been obsoleted by RFC 1812. This says ``The IP datagram SHOULD contain as much of the original datagram as possible without the length of the ICMP datagram exceeding 576 bytes'' (576 is the minimum MTU that the (IPv4<sup>28</sup>) Internet should support without fragmentation). The reason given for this is ``the use of IP-in-IP tunneling and other technologies''. Note that RFC 1812 only applies to routers, not hosts, but many ICMP errors (probably most that would use the extra information) will be generated by routers rather than hosts.

p. 82

RFC 1812 says that routers SHOULD NOT originate ``Source Quench'' errors (of course, they may forward them if originated at a host). The justification is that experiments show that generating ``Source Quench'' (which is ignored by UDP anyway, at least under Berkeley UNIX) actually consumes bandwidth and router resources, so is counter-productive.

p. 82

ICMP error 12 code 1 (required option missing) is used in the US DoD part of the Internet to indicate that a required security option is missing.