TCP stands for Transmission Control Protocol and is one of the core protocols of the Internet Protocol Suite. TCP complements the Internet Protocol (IP), and therefore the entire suite is commonly referred to as TCP/IP.

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Does pipelineing HTTP requests really result in faster page loads? Why?

A frequently cited argument is basically the one contained in this picture However, this does not reflect the reality of an underlying TCP connection which has to slowstart, and where the client ...
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88 views

in a browsing session, is it possible that web server initiates the TCP tear-down process?

when a user use browser to visit a website, it is the browser who initiates a TCP tear-down , namely it is the browser who sends the FIN/ACK first. is it possible that web server sends the FIN/ACK ...
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1answer
112 views

Hexadecimal Values Are Seemingly Backwards When Analyzing Packets Using Wireshark

Using Wireshark I am trying to debug an error that I am experiencing with one of my applications. I am having difficulty understanding how the packet contents are being formatted and displayed in ...
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1answer
207 views

how to maintain a inactive TCP connection?

if a TCP server establishes a TCP connection with a TCP client. Then the TCP client never sends any packet to the server. I roughly know firewalls near the TCP server may send a RST to it. or there ...
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3answers
787 views

should every TCP data packet be acknowledge or not? [closed]

If a tcp program A send two data packets to another TCP program B, packet 1: sequence number from 1000 to 2000; packet 2: seq number from 2000 to 3000. Generally B should reply with 2 ACKs, one for ...
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1k views

can TCP client use the same port to connec to different remote TCP servers?

I'm wondering whether TCP client can use the same port to connec to different remote TCP servers or not? In network-programming, there are two functions: sendto and send. When WE use send we don't ...
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1answer
266 views

Is it possible that a web server initiates a tcp connection to a browsing client? [closed]

when users use browser to visit a web site, it is of course the client send TCP SYN to initiate a tcp connection with the web server. I'm wondering are there any cases that a web server initiates a ...
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1answer
196 views

Router/NAT and IP/TCP header checksum

We know that IP/TCP has checksum mechanism to guarantee communication reliability. However, when a IP/TCP packet is relayed by router or NAT, the IP header may be modified, if if the router/NAT ...
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1answer
136 views

Gaining insight on TCP traffic

I have an iMac on which I turned off almost all applications. Browser, Skype, Spotify all turned off. Despite that, when I do a tcpdump I record still a lot of TCP traffic. How can I get insight into ...
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1answer
178 views

How does TCP get the MSS values for a certain path?

when a TCP client initiates a TCP connection with a remote TCP server, it will announce its MSS in the TCP option. I'm at a loss how TCP knows the path MSS value. This value is specific to the path ...
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1answer
139 views

Where can I find a table of TCP header options, which lists the kind number and corresponding option [closed]

Several days ago I came across a table of common TCP header options (tens of them), which lists the kind number and corresponding option, now I can't find it through google. like kind ...
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2answers
156 views

If there are 2 NICs on the same machine, can a TCP client on one NIC connect to a TCP server on the other NIC?

I use TUN/TAP to create a tun NIC tun0 with IP 10.10.10.2, and I have a real NIC eth0 with IP 202.112.34.49 Then I run a TCP client which binds its socket to 202.112.34.49 and a TCP server binding ...
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33 views

Can anyone explain how the loopback interface works? [duplicate]

I got to understand how TUN/TAP works from the following illustration: TUN/TAP illustration I'm at a loss how the loopback interface works. Can anyone explain a bit about how the loopback interface ...
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1answer
48 views

is it possible to update tcp window scaling factor after 3-way handshake by sending a syn/ack?

tcp window scaling factor is notified during 3-way handshake period is it possible to update tcp window scaling factor after 3-way handshake for example, by sending a SYN/ACK with tcp header option ...
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1answer
51 views

TCP vs UDP Error-Checking

I've bounced upon two articles that describe in-depth on how TCP and UDP connections work. However there is some kind of inconsistency. Where one article tells me that UDP does no Error-Checking at ...
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1answer
2k views

The best way to do TCP/IP over USB on Linux

I want to establish a TCP/IP link between two Linux machines that have several USB 2.0 ports as the only connection options. Since both host and slave ports are available, I can connect them via a ...
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2answers
91 views

Port forwarding beginner

I have been trying to set up port forwarding for the past 48 hours and I can't quite get it. I have used online port scanners to see what ports are open and they are saying none, not even the port I ...
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2answers
80 views

Sending TCP command from external network to specific device in home network

I'm working on a mobile phone application which has to send a TCP command to from external network (like a coffee shop or it's connecting to 3G) to a specific device in home network. Let's say A ...
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1answer
278 views

DNS: can't dig 8.8.8.8 directly

me@ubuntu:# dig @8.8.8.8 google.com ; <<>> DiG 9.9.2-P2 <<>> @8.8.8.8 google.com ; (1 server found) ;; global options: +cmd ;; connection timed out; no servers could be ...
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1answer
526 views

Scapy: TCP Retransmission error

I've been using Scapy to send SCCP or Skinny packets to my Cisco Desk Phone. However I keep getting these TCP Retransmission errors, and I believe this is causing the Cisco Phone to not respond. I ...
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1answer
824 views

MTU, RWIN, and MSS

I have been doing some reading into TCP Receive Window (RWIN), Maximum Segment Size (MSS) and Maximum Transmission Unit (MTU). Right off the bat I have some questions and I need a power user's help! ...
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261 views

How to use NetLimiter to block inbound TCP traffic?

I'm using NetLimiter to block TCP traffic. (Rule type: Firewall, Direction: In, Action: Deny) I can block outbound, but not inbound. You can try blocking inbound TCP on Chrome to see it is not ...
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3answers
2k views

How to pipe data over tcp from the command line?

I would like to pipe data from one machine in the command line to another machine over tcp. I guess I could write a socket server but this must already be implemented. For example I could use it to xz ...
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182 views

how tcp stack deal with the ack_seq number and seq number of tcp FIN/ACK packet?

from my knowledge, seq and ack_seq are processed by tcp stack independently. when a packet arrives with a inconsistent ack_seq number if: 1) the ack_seq number is obsolete(smaller than expected), ...
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1answer
54 views

Automating an IP Phone

I've been very interested in Automating an IP phone, currently I am automating phone calls by using PuTTY to a Dial-Up modem through simple AT commands. However, this is a poor method because it does ...
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1answer
954 views

Can't connect to SSH over VPN when using 3G only

I'm having a bit of a strange problem that I'm not sure how to debug/fix. I have a Raspberry Pi connected to a Windows VPN via either a wired interface or 3G dongle. With the wired interface I can ...
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2answers
227 views

TCP Throughput versus Packet Loss

How does the packet loss rate affect the TCP throughput rate: throughput rate reduce exponentially with respect to loss increase or throughput rate reduces by the same amount as loss increase?
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1answer
161 views

find the process which is listening on a specific port

I want to find some processes which are running on a specified port for example 80 I ran fuser 80/tcp and got nothing and then netstat -tulpn|grep "80\|PID" and got Proto Recv-Q Send-Q Local ...
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3answers
9k views

TCP Retransmission vs. TCP Fast Retransmission

In Wireshark I can see things that say "TCP Retransmission" and "TCP Fast Retransmission." What's the difference? How is Wireshark able to tell the difference?
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1answer
330 views

Testing network equipment, TCP window size matters

We are currently testing some network equipment (consumer routers with 1 Gbit/s ports) with Jpef 2.0. All kinds of connection parameters are tested: wired and wireless, different wireless standards, ...
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1answer
699 views

using iptables to prevent RST related to a specific port

I have a program which uses libpcap to capture incoming TCP SYN packets, these SYN packets are destined for a specific port. But I have no tcp listening socket for that port, so in practice, the OS ...
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3answers
372 views

How can I open a TCP/UDP connection on Linux?

I am looking for a simple command line tool to open TCP/UDP server/client on a desired port on a Linux machine. Are there any applications or commands that I can use to achieve this?
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2k views

Connecting Android via wifi to Wifly RN-XV RN-171 using Access Point (soft AP) mode not working

I hope somebody has encountered this problem and knows how to fix it. I purchased a Roving Networks RN-XV module to communicate directly with an Android device. I thought it would be perfect because ...
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1answer
163 views

Why does Knoppix mess up my internet connection?

I have this problem that when I boot Knoppix on my Windows box, it screws up the internet connection somehow, so Windows cannot get an IP when I reboot back to XP. I use Verizon FIOS. Normally I have ...
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1answer
115 views

How to set TCP SEQ number generation

There is a Windows 2000 system, that when I scanned it, it said, that the TCP SEQ number prediction is really low (nmap – trivial joke). While I'm still trying to verify that, I wondered, how could ...
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2answers
5k views

What do these remote addresses, local addresses, and states in TCPview mean?

I have been using TCPview lately to see what connections are made by different processes on my PC. Would somebody please explain what the following situations mean? Thanks. TCP Local Address: ...
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1answer
478 views

Is it possible for a PC to use two net connections simultaneously?

We have two net connections in our office - a 10mb Wired DSL provider and a 3mb Wireless backup provider. The wireless is a backup, but it has the advantage of 3mb upload speeds whereas the wired is ...
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1answer
162 views

How do NAT or proxy react to incoming TCP SYN packet?

In some messaging systems, two messaging clients send/receive packets directly from each other in chatting or voice call. I think the basic mechanism is (TCP for example): these client programs open a ...
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8answers
1k views

How to make Firefox use TCP for DNS

I want to use TCP for DNS, to bypass my ISP's slow and broken DNS servers. I'm not using (and don't want to use) a proxy. Note: I want to use DNS over TCP because if I use it over udp, no matter what ...
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1answer
360 views

Virtual Windows Server 2008 R2 system unexpectedly responds on TCP echo port 7

We have a virtual system running Windows Server 2008 R2, and it responds on TCP port 7 (echo). (I.e, in response to a SYN it sends ACK,RST, which is enough to make InetAddress#isReachable() return ...
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0answers
347 views

intercept TCP/UDP Packets on a host before they are sent to or recevied from the network [closed]

for example, 1 when I'm using some programs, like visiting websites using firefox if the webserver send my program some data, my program TCP stack will issue an ACK packet. Is it possible to ...
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1answer
773 views

is tcp header timestamp mandatory or optional? and how to generate tcp timestamp

I noticed that in all tcp communications, in the tcp header option parts, tcp timestamp is always there is it mandatory or not? so if there is no tcp timestamp in a tcp packet, the tcp client or ...
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1answer
2k views

How is TCP/UDP checksum working?

I used raw socket to create some UDP packets and then send them to a UDP server I notice that when I put a wrong UDP checksum number the UDP server doesn't accept it, but if I put all 0 on the ...
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1answer
71 views

sent packet is different from received packet

I use raw socket to create TCP packets, with focus on the sequence number and TCP flags(SYN, ACK) I used one machine S to send a tcp ACK packet (flag ACK is set to 1) and another machine R to receive ...
2
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0answers
762 views

tcp port numbers reused on wireshark

I used raw socket to build a tcp client program on machine A to reproduce tcp 3-way handshake with a simple regular tcp server on machine B I captured packets on the client host and server host, and ...
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1answer
313 views

stopped a service but outgoing port still exists on netstat -aon

bit more detail.... I have a port, specifically port 2869 for Windows Media Player Network Sharing Service that uses UPnP port 2869, however even when turning off all the sharing possibilities I can ...
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1answer
169 views

TCP number of connections differ from client to server

How can this be ? netstat shows x 'established' connections from the client to y 'established' connections on the server. Situation stays like this for 10 minutes, then x and y change, then another ...
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1answer
141 views

How does the browser know which packet is the response to a specific request?

I am sniffing the in/out packets over TCP. I have some GET output, but I want to know which of the packets is the input? How does the browser determine this? Simpler explaination: I'm sniffing and I ...
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1answer
5k views

Remotely push DNS server to client via OpenVPN

When I try to push a DNS server via the OpenVPN server-config I don't get that server to be the first DNS server on the connected client system. It ends up being specified as an alternative DNS ...
3
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1answer
2k views

Is there a way to kill an open connection without killing the process?

I've search around and all the suggestions just say to kill the process. But I'm surprised I can't find any simple way to force a "connection" to close, without killing a pid associated with it. ...