UNIX System Administration Handbook - Evi Nemeth [205]
4. This is a small lie that’s true in most situations. See the discussion of NAT starting on page 279 for the straight dope on nonunique IP addresses.
5. Another lie in the name of a simple, as yet incomplete description; see the discussion of Classless Inter-Domain Routing (CIDR) on page 276 for the real scoop.
6. The original Ethernet on RG-11 coaxial cable allowed at most 1,024 hosts on a single network, probably because of the maximum length of a cable and the separation required between hosts. This limit might still be lurking in code today, so this arrangement would not be practical for the real world.
7. But be careful not to back yourself into a corner ... This puzzle is left as an exercise for the reader.
8. When we started writing this chapter in the summer of 1999, the number of routes in the backbone table was 60,000. Now, less than a year later, it is 80,000—that’s more than 25% growth per year. Current routing hardware and algorithms can sustain a few percent growth per year, but not 25%. See www.telstra.net/ops/bgp/index.html for more information.
9. A new registry is being created for Latin America, but it won’t be operational for a while.
10. Strictly speaking, Red Hat does not support NAT, but rather PAT (port address translation). It uses the IP address of the machine doing the translation as the only “external” address and uses the source port number as a basis for multiplexing connections.
11. CAIDA, pronounced “kay duh,” is the Cooperative Association for Internet Data Analysis at the San Diego Supercomputer Center on the UCSD campus (www.caida.org).
12. Except on point-to-point links, on which the identity of the destination is sometimes implicit.
13. Routers can often be configured to flood broadcast packets to other networks; don’t do this.
14. ARP uses the underlying link layer’s broadcasting conventions, not IP broadcasting.
15. Each of the DHCP protocol message types begins with “DHCP.” We’ll leave out the DHCP from now on to make the text easier to read.
16. Be careful: the dhcpd.conf file format is a bit fragile. Leave out a semicolon, and you’ll receive an obscure, unhelpful error message.
17. PPP is normally used at speeds over 19,200 bps. Technically, it can be used on slower links, but it becomes insufferably slow.
18. However, some versions of routed will overwrite static routes.
19. /etc/networks can be used to map names to network numbers much like the /etc/hosts file maps hostnames to complete IP addresses. Many commands that expect a network number can accept a network name if it is listed in the /etc/networks file (or in DNS, on some systems).
20. Solaris network interfaces must be scoped out with ifconfig plumb to make them accessible. You might have to run this command by hand when performing manual configuration.
21. The netmasks man page is broken on Solaris 7; it is fixed in later versions.
22. routed has no access controls and believes everything it hears. A host running routed -q listens but doesn’t talk; without the -q, the host can advertise routes. A confused host can really mess up your network because every other routed will believe its advertisements.
23. On HP-UX 11, the hop count field is not required; it defaults to 0 if not explicitly specified. Earlier versions required the count field to be present.
24. A pump, like a boot (as in BOOTP), is a type of footwear.
25. If you try this command in the form sudo echo 1 > icmp_echo_ignore_broadcasts, you’ll just generate a “permission denied” message—your shell attempts to open the output file before it runs sudo. You want the sudo to apply to both the echo command and the redirection. Ergo, you must create a root subshell in which to execute the entire command.
26. Strictly speaking, Red Hat performs only a limited form of NAT which is more properly called PAT, for Port Address Translation. Instead of using a range of IP addresses