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1 Figure 3-27: Use of TCP and UDP Port Number Client 60.171.18.22 From: 60.171.18.22:50047 To: 60.171.17.13:80 SMTP Server 123.30.17.120 Port 25 Webserver 60.171.17.13 Port 80
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2 Figure 3-27: Use of TCP and UDP Port Number Client 60.171.18.22 From: 60.171.17.13:80 To: 60.171.18.22:50047 SMTP Server 123.30.17.120 Port 25 Webserver 60.171.17.13 Port 80 From: 60.171.18.22:50047 To: 60.171.17.13:80
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3 Figure 3-27: Use of TCP and UDP Port Number From: 60.171.18.22:60003 To: 123.30.17.120:25 Client 60.171.18.22 SMTP Server 123.30.17.120 Port 25 Webserver 60.171.17.13 Port 80
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4 Figure 3-27: Use of TCP and UDP Port Number From: 60.171.18.22:60003 To: 123.30.17.120:25 Client 60.171.18.22 From: 60.171.18.22:50047 To: 60.171.17.13:80 SMTP Server 123.30.17.120 Port 25 Webserver 60.171.17.13 Port 80 Clients Used Different Ephemeral Ports for Different Connections
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5 Figure 3-29: User Data Protocol (UDP) (Study Figure) UDP Datagrams are Simple (Figure 3-30) Source and destination port numbers (16 bits each) UDP length (16 bits) UDP checksum (16 bits) Bit 0 Bit 31 IP Header (Usually 20 Bytes) Source Port Number (16 bits)Destination Port Number (16 bits) UDP Length (16 bits)UDP Checksum (16 bits) Data Field
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6 Figure 3-29: User Data Protocol (UDP) (Study Figure) Port Spoofing Still Possible UDP Datagram Insertion Insert UDP datagram into an ongoing dialog stream Hard to detect because no sequence numbers in UDP
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