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Understanding the network.pdf - Back to Home

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The client <strong>the</strong>n sends an ACK back <strong>to</strong> <strong>the</strong> server. Now <strong>the</strong> dedicated<br />

VC is established and full duplex data exchange can take place.<br />

TCP ports can support many simultaneous connections or processes.<br />

TCP keeps <strong>the</strong>se processes organized by using <strong>the</strong> process endpoints<br />

<strong>to</strong> track <strong>the</strong> connections. The endpoint address is <strong>the</strong> process port<br />

number plus <strong>the</strong> IP address of <strong>the</strong> host that started <strong>the</strong> connection. In<br />

this example, <strong>the</strong> process endpoint on <strong>the</strong> server would be<br />

192.160.33.20.2200 and <strong>the</strong> process endpoint on <strong>the</strong> client would be<br />

90.16.44.8.25. The most common TCP service ports are listed in<br />

Table 2.12.<br />

Table 2.12. Common TCP Service Ports<br />

Port Number Service<br />

1 TCPMUX<br />

21 FTP<br />

20 FTP-DATA<br />

22 SSH (Secure Shell)<br />

23 Telnet<br />

25 SMTP<br />

53 DNS (Domain Name Service)<br />

80 HTTP (WWW)<br />

139 WINS<br />

119 NNTP (Network News Transport Pro<strong>to</strong>col)<br />

110 POP3 (Post Office Pro<strong>to</strong>col)<br />

543 Klogin (Kerberos login)<br />

544 Kshell (Kerberos shell)<br />

751 Kpasswd (Kerberos password)<br />

750 Kerberos server<br />

512 Berkeley rcommands<br />

513 login<br />

443 HTTPS secure WWW server<br />

2105 eklogin (encrypted Kerberos login)<br />

2049 NFS (Network File System)

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