packet sniffer

them in the/etc/services file of Linux.FTP-data 20/tcpFTP 21/tcpTelnet 23/tcpSMTP 25/tcp mailWWW 80/tcp HTTP # worldwideweb HTTPWWW 80/udp # Hypertext Transfer ProtocolPop-3 110/tcp # Pop Version 3Pop-3 110/udp In fact, the port number can be used with any services you like to specify, but in order to avoid "finding the wrong door" (unless you deliberately want to hide) people will use some of the more common services (wellKnownServices. However, in the TCP data transmission process, more than

, as determined by target: A. Continue to match next rule B. Make some changes to the packet C. Jump to another chain (that is, start by matching each rule in the chain sequentially) D. Returns the chain that raised the jump (that is, the next rule that continues to match the chain before the jump) E. Drop packet F. Receive packets (i.e. no longer continue to match down, return directly) G. Logging

origin:http://blog.csdn.net/e_wsq/article/details/12835457 For the TCP-based development of the communication program, there is a very important problem to be solved, that is, the packet and unpacking. Since I've been working on network communication programming (about three years), I've been thinking about and improving the way that packets and unpacking are addressed. Here's what I think about this question. If it's wrong, The wrong place, begged ev

Group First, let's look at the concept of the next grouping. The so-called grouping is to divide a packet into smaller packets. For example, for a 10GB packet, it is not always a one-time delivery of the past bar, but it is divided into a number of small packets sent past. Structure diagram for each block of data:File headers are typically descriptive data, such as source and destination addresses, data typ

Transferred from: http://cizixs.com/2018/01/13/linux-udp-packet-drop-debug?hmsr=toutiao.ioutm_medium=toutiao.ioutm_ Source=toutiao.ioRecent work encountered a server application UDP packet loss, in the process of reviewing a lot of information, summed up this article, for more people to refer to.Before we get started, we'll use a graph to explain the process of receiving network messages from a Linux system

on the network. Therefore, the network analysis tools in the system are not a threat to the security of the local machine, but a threat to the security of other computers on the network. Tcpdump is defined as simple as possible, namely: dump the traffice on anetwork. a packet analysis tool that intercepts packets on the network according to the user's definition. As a necessary tool for the classic system administrator on the Internet, tcpdump, with

transmits data packets, if the length of the IP datagram plus the data frame header is greater than MTU, the data packets are divided into several parts for transmission and reorganized in the target system. For example, the maximum IP packet size (MTU) that can be transmitted over Ethernet is 1500 bytes. If the size of the data frame to be transmitted exceeds 1500 bytes, that is, the IP datagram length is greater than 1472 (1500-20-8 = 1472, normal

1. Circuit Switching Technology The network switching technology has gone through four stages: Circuit Switching Technology, packet switching technology, group switching technology and ATM technology. Both the Public Telephone Network (PSTN) and the mobile network (including the GSM network and CDMA network) Adopt the circuit switching technology. Its basic feature is that the connection-oriented approach is adopted before both parties can communicate

of the IP datagram plus the data frame header is greater than MTU, the data packets are divided into several parts for transmission and reorganized in the target system. For example, the maximum IP packet size (MTU) that can be transmitted over Ethernet is 1500 bytes. If the size of the data frame to be transmitted exceeds 1500 bytes, that is, the IP datagram length is greater than 1472 (1500-20-8 = 1472, normal datagram) bytes, the data frame needs

Basic use of the packet capture tool EtherealThis is a tutorial written by enthusiastic people on the Internet. I have put it into practice and it is very simple, but the basic work is enough. I will organize it for the moment.You can perform basic packet capture according to the steps. 1. Use the prefix parameter settings -- capture option settings Interface: Specifies the interface (NIC) on which the

The protocol number for OSPF is 89, and when OSPF packet multicasting occurs, their TTL is set to 1,1. Packet headerAll OSPF packets are started by a 24-byte eight-bit group header650) this.width=650; "Style=" Background:url ("/e/u261/lang/zh-cn/images/localimage.png") no-repeat Center;border : 1px solid #ddd; "src="/e/u261/themes/default/images/spacer.gif "alt=" Spacer.gif "/>650) this.width=650; "Style="

this This paper mainly introduces the realization of WEBRTC in Nack, Weizhenwei, the article was first published in the Wind network , Id:befoioSupport original, reprint must indicate the source, welcome attention to my public number blacker (Id:blackerteam or WEBRTCORGCN).In WEBRTC, forward error correction (FEC) and packet loss retransmission (NACK) are important methods to resist network errors. FEC adds a redundant error-correcting code to the

used to specify the maximum life cycle of each packet on the Internet. Each intermediate router reduces the TTL value by one before forwarding the IP packet to the next hop. A. Extract the final TTL value When a data packet arrives at the destination address to extract the TTL field value, this value is called the final TTL value. The challenge of hop count stat

Author: sodimethyl Source: http://blog.csdn.net/sodme statement: This article can be reproduced, reproduced, spread without the consent of the author, but any reference to this article please keep the author, source and this statement information. Thank you!The common network servers are basically 7x24. For online games, at least require the server to work continuously for more than a week and ensure that no catastrophic event such as server crash occurs. In fact, it is almost unrealistic to req

The 1th chapter, router-based packet filtering firewall General concepts of 1.1 packet filtering firewalls 1.1.1 What is a packet filter firewall A packet filtering firewall is a software that looks at the header of the packet that flows through it, thus determining the fate

I don't know how to say it. In short, the boat, from the mouth, I can not see HUANGFA and impoverished! I'm not going to say anything except cursing!Prior to BBR, there are two kinds of congestion control algorithms, based on packet loss and delay-based, regardless of which is based on detection, in other words, packet loss based on packet loss as a means to find

Packet Capture analysis tool-tcpdump Tcpdump (dump the traffic on a network) is a more practical tool for analyzing data packets in Unix, it supports filtering at the network layer, protocol, host, network or port, and provides logical statements such as and, or, not, and boolean expressions for packet header matching, in Linux, you can use yum to install yum if it is not installed. However, you need the fo

Document directory TCP packet TCP Reliability Assurance TCP data packets Source Port and destination port field -- each occupies 2 bytes. Identifies the application process of the sender and receiver. Number Field-4 bytes. Each byte in the data stream transmitted in the TCP connection is a serial number. The value of the serial number field refers to the sequence number of the first byte of the data sent in this section. The validation number

In the last lecture, we learned how to get the appropriate information, this one will let us write a program Chiang every packet printed through the adapter.The function that opens the device is Pcap_open (). function prototypes arepcap_t* pcap_open (const char* source,int snaplen,int flags,int read_timeout,struct pcap_rmtauth *auth,char * errbuf); 'Pcap_rmatauth{int type.Char *username;;/ /zero-terminated string containing the username that have to i

There are three scenarios when a packet passes through a firewall:1. Local-Targeted packagesWhen a packet enters the firewall, if the destination address is native, the order in which the firewall is checked is as follows:If a packet is discarded at one step, no subsequent checks are performed Steps Table Chain Description