Cirrus Logic CS485 Bedienungsanleitung PDF herunterladen (Seite 64)

CS485G Spring 2015 64

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dresses in region.

(d) Special purpose addresses: ﬁrst octet 225-255.

(e) This division into classes is no longer followed.

(f) A network ID is written in the form w.x.y.z/n, where n is the

number of bits in a host address. For instance, CS uses the class

C region 128.163.146/8.

(g) Some regions are pre-allocated as private, unrouted addresses:

10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16.

16. Human-readable host names

(a) The Domain Name Service (DNS) maps IP addresses into a hi-

erarchy of names.

(b) First-level domain names: .net, .edu, .gov, .com

(d) Third level: cs, www.

(e) No limit on levels, and no particular conventions.

(f) The mapping is maintained in a huge distributed database, which

can be understood as a collection of host-entry structures.

1 struct hostent {

2 char

h_name;

official domain name of host

3 char

h_aliases;

null-terminated array of domain names

4 int h_addrtype;

host address type (AF_INET)

5 int h_length;

length of an address, in bytes

6 char

h_addr_list; /

null-terminated array of in_addr structs

7 }

(g) The gethostbyname() library call queries the DNS database.

(h) Queries in Unix are ﬁrst checked in /etc/hosts. If that fails,

they are sent to a name server, as listed in /etc/resolv.conf.

(i) Command-line programs: nslookup, dig (Domain Informa-

tion Groper)

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Cirrus Logic CS485 Bedienungsanleitung Seite 64