tcp udp port scan

httpNmap done: 1 IP address (1 host up) scanned in 1274.21 seconds 3.2nmap also has a reason to perform UDP scan, such as some UDP-based services, SNMP, TFTP, DHCP, DNS, etc. [emailprotected]:~# nmap -sU 192.168.115.188Starting Nmap 6.47 ( http://nmap.org ) at 2014-10-23 20:21 CSTNmap scan report for 192.168.

means this is a sack packet length of 2, no content part 8 indicates a timestamp, length is 10, and 8 bytes of time stamp*/ typedef struct _TCP_OPTIONS{Char M_ckind;Char m_clength;Char m_ccontext[32];}__ATTRIBUTE__ ((Packed)) tcp_options, *ptcp_options; the definition of UDP head structure /*UDP header definition, total 8 bytes */ typedef struct _UDP_HEADER{unsigned short m_ussourport; Source

information is transmitted, a response signal is required when the connection is disconnected, which increases the resource overhead for the connection protocol. For TCP and UDP protocols, apart from the source port and destination port, TCP also includes serial number, val

M_ssourport; Source Port number 16bitShort M_sdestport; Destination port number 16bitunsigned int m_uisequnum; Serial number 32bitunsigned int m_uiacknowledgenum; Confirmation Number 32bitShort M_sheaderlenandflag; Top 4 bits: TCP header length, medium 6 bit: reserved, last 6 bits: Flag bitShort m_swindowsize; Window Size 16bitShort m_schecksum; Inspection and 1

-65535, generally we use a certain software, such as QQ, and other services, randomly take this range of ports, rather than to get the front of which fixed, get the communication end, will release the port.Know what the port is? What did the transport layer specifically do? Transport layer is to connect two ports to communicate media, otherwise the light knows what two ports are used, how to communicate, or to rely on transport layer to do this thing,

port number with a unique identity on the network can be combined to form a uniquely identifiable identifier socket. socket principle mechanism:? There are sockets on both ends of the communication. ? network communication is actually the communication between sockets. ? data is transmitted via IO between two sockets. UDP Transport Datagramsocket and Datagrampacket establish the sending end, t

wait for the response from the receiver and confirm whether the information is transmitted, a response signal is required when the connection is disconnected, which increases the resource overhead for the connection protocol. For TCP and UDP protocols, apart from the source port and destination port,

oriented;In the UDP protocol, recvfrom this receive function will always remain blocked, because the server itself does not know that the client has exited or disconnected, proving that it is facing a non-connected.It can also be clearly seen that TCP communication requires the server to listen for listen, receive client connection request accept, wait for the client connect to establish a connection befor

receives the closed request message, it returns a confirmation message to the server, in which the ack=1, acknowledge Number=n+1,client enter the TIME_WAIT state. After the server receives the acknowledgement message, it disconnects from the client, and the two-way connection is closed.4. UDP Message Header formatUDP is similar to TCP is the Transport layer protocol, is also based on IP protocol, so in the

. Description of Use: Solve the data in the network can be transmitted efficiently Relationship Description: In the OSI reference Model, only TCP and UDP two, TCP need link security efficiency is low, UDP wireless connection is not safe and efficient, we usually use long HTTP protocol based on

data. The value is the ordinal of the last 1 bytes of the emergency data, which represents the offset of the message segment ordinal. For example, if the sequence number of the message segment is 1000 and the first 8 bytes are emergency data, then the emergency pointer is 8. The general purpose of the emergency pointer is to enable the user to abort the process. One) option, fill field This may include options such as window enlargement factor, timestamp, and so on. The length is