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Chapter 10 Local Area Network Security > TCP SYN (Half-Open) Scanning

TCP SYN (Half-Open) Scanning

This technique is often referred to as half-open scanning because you don’t open a full TCP connection. You send a SYN packet, as though you were going to open a real connection, and wait for a response. A SYN|ACK indicates that the port is listening. An RST is indicative of a nonlistener. If a SYN|ACK is received, you immediately send an RST to tear down the connection (actually, the kernel does this for you). The primary advantage of this scanning technique is that fewer sites will log it! SYN scanning is the -s option of Nmap.


[**] [1:0:0] DOS Teardrop attack [**]
[Priority: 0]
01/26-11:37:10.667833 192.168.1.20:1631 -> 192.168.1.22:21
UDP TTL:128 TOS:0x0 ID:60940 IpLen:20 DgmLen:69
Len: 41
[**] [1:0:0] DOS Teardrop attack [**]
[Priority: 0]
01/26-11:37:10.668460 192.168.1.20:1631 -> 192.168.1.22:21
UDP TTL:128 TOS:0x0 ID:60940 IpLen:20 DgmLen:69
Len: 41
[**] [1:0:0] DOS Teardrop attack [**]
[Priority: 0]
01/26-11:37:11.667926 192.168.1.20:1631 -> 192.168.1.22:21
UDP TTL:128 TOS:0x0 ID:60941 IpLen:20 DgmLen:69
Len: 41
[**] [1:0:0] DOS Teardrop attack [**]
[Priority: 0]
01/26-11:37:11.669424 192.168.1.20:1631 -> 192.168.1.22:21
UDP TTL:128 TOS:0x0 ID:60941 IpLen:20 DgmLen:69
Len: 41
[**] [1:0:0] DOS Teardrop attack [**]
[Priority: 0]
01/26-11:37:12.669316 192.168.1.20:1631 -> 192.168.1.22:21
UDP TTL:128 TOS:0x0 ID:60942 IpLen:20 DgmLen:69
Len: 41


  

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