tyt09fi.htm

一个学习tcp/ip协议的教程

# ping -c5 147.120.0.1

PING 147.120.0.1 (147.120.0.1): 56 data bytes

64 bytes from merlin (147.120.0.1): icmp_seq=0 ttl=64 time=0 ms

64 bytes from merlin (147.120.0.1): icmp_seq=1 ttl=64 time=0 ms

64 bytes from merlin (147.120.0.1): icmp_seq=2 ttl=64 time=0 ms

64 bytes from merlin (147.120.0.1): icmp_seq=3 ttl=64 time=0 ms

64 bytes from merlin (147.120.0.1): icmp_seq=4 ttl=64 time=0 ms

--- 147.120.0.1 ping statistics ---

5 packets transmitted, 5 packets received, 0% packet loss

round-trip min/avg/max = 0/0/0 ms</FONT></PRE><P>In the preceding example, issued on the server merlin with IP address 147.120.0.1, I used the ping command with the -c option to specify how many packets to send. As you can see, both the localhost and IP address responded properly, indicating that the TCP/IP software is properly loaded and the IP address is recognized.<BR><P>As you saw earlier today, UNIX TCP/IP networking software relies on several files for configuration. These were summarized in Table 9.2. You can look at each of these files now with respect to the SCO UNIX server on the sample network.<BR><P>The /etc/hosts file contains the names of the other machines on the network and their network addresses. The file looks like this:<BR><PRE>

<FONT COLOR=#000080>#      @(#)hosts    1.2 Lachman System V STREAMS TCP  source

#      SCCS IDENTIFICATION

127.0.0.1           localhost tpci

147.120.0.1         merlin merlin.tpci.com

147.120.0.2         freya freya.tpci.com

147.120.0.3         brutus brutus.tpci.com

147.120.0.4         megan megan.tpci.com_

147.120.0.10        whitney whitney.tpci.com

147.120.0.11        sinbad sinbad.tpci.com

147.120.0.12        pepper pepper.tpci.com</FONT></PRE><P>Each line contains the local machine name and its full name with the domain so that either version is recognized by the operating system. As new machines are added to the network, new lines are added to the file. The local machine has two entries in the file: one for the local name and one for localhost.<BR><P>The /etc/networks file holds a list of network names and their addresses. This is an optional file as far as most TCP/IP installations are concerned, and most system administrators use it only when the users need it. The /etc/networks file lets you name networks in the same way as machines. The following example shows some of the SCO network machines as well as two networks that the local machines frequently connect to. Using the name maclean_net as part of a machine identifier supplied by a user is now possible because the operating system can resolve it to its IP address through this file.<BR><PRE>

<FONT COLOR=#000080>#      @(#)networks 1.2 Lachman System V STREAMS TCP  source

#      SCCS IDENTIFICATION

loopback       127

sco            132.147

sco-hq         132.147.128

sco-mfg        132.147.64

sco-engr       132.147.192

sco-slip       132.147.32

sco-tcplab     132.147.160

sco-odtlab     132.147.1

maclean_net    147.50.1

bnr.ca         47</FONT></PRE><P>On Day 6 &quot;Telnet and FTP,&quot; you examined the /etc/services file. It includes information about all the TCP and UDP services supported by the system. For the sample network and most small networks, the default values are acceptable. These entries are changed only if a service is being removed from TCP/IP, such as to prevent Telnet access. The file looks like this:<BR><PRE>

<FONT COLOR=#000080>#      @(#)services 5.1 Lachman System V STREAMS TCP  source

#

#    System V STREAMS TCP - Release 4.0

# Network services, Internet style

#

echo            7/tcp

echo            7/udp

discard         9/tcp         sink null

discard         9/udp         sink null

systat          11/tcp        users

daytime         13/tcp

daytime         13/udp

netstat         15/tcp

qotd            17/tcp        quote

chargen         19/tcp        ttytst source

chargen         19/udp        ttytst source

ftp             21/tcp

telnet          23/tcp

smtp            25/tcp        mail

time            37/tcp        timserver

time            37/udp        timserver

rlp             39/udp        resource       # resource location

nameserver      42/tcp        name           # IEN 116

whois           43/tcp        nicname

domain          53/tcp        nameserver     # name-domain server

domain          53/udp        nameserver

mtp             57/tcp                       # deprecated