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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Is it possible to suspend a socket (SSH session, specifically) to switch network devices?

When resuming a tmux workspace on my laptop, I regularly have to decide between the wired and WiFi connection. Ethernet has very low latency, but forces me to reconnect any time the laptop is moved. ...
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1answer
3k views

Wireshark - How do i filter the TCP[RST] packet?

I am looking for filter out the TCP[RST] packets on wireshark. I have tried tcp.analysis.flag but it didn't help.
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263 views

Firewall is blocking echo request on port 7 (TCP)

I have an app which needs to receive a message back from the server. With the firewall on, I do not get the message back. If I turn off the firewall I get the request back. I have added some rules ...
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1answer
6k views

Windows 7 firewall causing remote connection to time out; should refuse connection

The Windows 7 Firewall is running with default options to allow outbound connections and block incoming connections. I have a process trying to connect regularly from within my local network, which is ...
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3answers
637 views

How to monitor TCP connections over time

I have an application which is a windows service. It accesses a number of other services using TCP/IP. E.g. sql server databases, informix databases, mail servers, etc. For instance it will also ...
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1answer
469 views

How does a proxy know where to forward the requests to?

When a proxy receives a connection how does the proxy know where to forward the request to? For example in Java we can set a system property for proxy. So we set the IP of the proxy and the request is ...
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3answers
1k views

Network Traffic per process/application windows

I know that there are plenty of applications to do this (like procexplorer) but is there anyway to access the winapi (what method/reference is used) to retrieve the network traffic (TCP, UDP, etc) per ...
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171 views

Data corruption after upgrading broadband speed and modem/router

I'm using an ISP called Fibertel in Argentina, and I recently upgraded my connection to 30 down/3 up. With this change came a new modem+router: the Motorola SBG 6580. Before I had something like 1 ...
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4answers
89 views

TCP/IP on the transport level

I'm trying to understand what happens when I send a packet using a socket on the transport level. Do all packets which leave my computer go first to a geographical location designated by my ISP? Then ...
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1answer
323 views

What type of TCP connections are counted?

In Windows 7's Resource Monitor, in the TCP Connections graph at the top right -- how are those connections being counted? Does a "listening" state count, for example? Does it matter what state a ...
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2answers
4k views

TCP: Maximum number of connections (client and server)

In the description of TCP in the Wikipedia, it is stated that The number of sessions in the server side is limited only by memory and can grow as new connections arrive, but the client must ...
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1answer
305 views

why TCP window scale values (scaling factor) are different in different hosts?

why TCP window scale values (scaling factor) are different in different hosts? why not make this value the same on all hosts? in theory, this value is between 0-14. what is the practical range for ...
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459 views

Are there any requirements for the sequence numbers on TCP Reset packets?

If there is a TCP connection between TCP program A and B, and its source IP address/port and destination IP address/port are known by an attacker, now the attacker wants to send a TCP Reset packet to ...
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9k views

what is TCP Half Open Connection and TCP half closed connection

I am trying to understand what is the difference between TCP Half Open Connection and TCP Half closed connection can any one tell what exactly are they?
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131 views

TCP video streaming: TCP throughput(rate) and RTT

we know that a rough estimation of TCP rate is: WINDOW/RTT, where WINDOW is the min(CWIN, RWIN), CWIN is the congestion window size of the sender, while RWIN is the receiving window. nowadays, the ...
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2answers
417 views

TCP SYN does not reach TCP server

I have a TCP server listening on 10.10.10.101, port 2000, running on a Windows 7 machine. Below is the corresponding output line for the command netstat -aon: TCP 10.10.10.101:2000 0.0.0.0:0 ...
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1answer
206 views

Find processes listening on the wildcard address in `lsof`

Using lsof, I can find all of the processes with a TCP socket listening for connections: lsof -Pni -sTCP:LISTEN e.g.: COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME cupsd 662 ...
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2answers
771 views

Why does TCP sometimes not acknowledge the packets it receives?

I use firefox to visit a web server running on a computer on my LAN. I notice that sometimes TCP doesn't acknowledge the packets it receives. For example, in the following captured packets: ...
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3answers
8k views

How exactly does a proxy work?

If I want to connect to say, IP 100.100.100.100, Port 80, my computer will send a tcp packet with this adress into the wire. Now If I use a proxy server say, 200.200.200.200 Port 8080 (such kind of ...
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2answers
5k views

TCP Slow start and congestion control, and how to modify them

I'm trying to change the behavior of the tcp slow start protocol on a CentOS5 box (uname -r => 2.6.18-238.12.1.el5). I have read that the following command will change my icwnd to 8: ip route change ...
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3answers
1k views

Open TCP port in Windows 7 and read incoming data, what program to use?

I have an external device which can connect over GPRS to the Internet using a SIM card and I want to see what data it sends. I can program it to use my computer as a server and then use a program to ...
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1answer
621 views

about combinations of TCP flags

TCP FIN packet, ACK flag is always set? In TCP tear-down phase, there are usually 4 packets: FIN/ACK, ACK, FIN/ACK, ACK. Is it possible some of these packets may not be sent by a TCP peer? When there ...
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398 views

TCP: when in TIME_WAIT state, will TCP starts a new 2MSL time if it receives a retransmitted FIN with 2MSL

we know that when a TCP program is in TIME_WAIT state, it waits for a FIN for 2MSL. if it receives a retransmitted FIN with 2MSL and retransmits an ACK, will it starts another 2MSL timeout or not?
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1answer
346 views

How to intentionally delay TCP packets in one direction

I've looked at this already: How to deliberately introduce a delay for incoming UDP packets I am testing a server-client system, and need to delay messages from the server to the client by some ...
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1answer
247 views

Disable tcp slow start

I am looking for disable tcp slow start mechanism for high-speed network. Currently clients send 100MB flows to random servers with non-blocking 1Gbps link. In my math, the completion time of the ...
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2answers
962 views

TCP header option: SACK-permitted (Selective Acknowledgments) negotiation

I'm doing a research project, which needs to split tcp connection. so I have some pecular questions, which may happen in my development. The problem is understanding of TCP SACK-permitted ...
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676 views

if a TCP packet got partially acknowledged, how will the retransmission mechanism react?

if a tcp client send a packet, with sequence number from 10000 to 20000, to a tcp server. the tcp will respond with an ACK with seq_ack 20001. if I intercept the TCP packet from the client, and ...
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1answer
718 views

Ports 1935 and 843 are getting blocked for no reason

I have Windows 7, and my computer has been blocking ports 1935 and 843 for no reason for a while now. If for example, I try to watch twitch, nothing will work because those two are getting blocked. ...
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142 views

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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1answer
106 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
126 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
257 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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1k 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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2answers
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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
329 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 ...
2
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1answer
277 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
149 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
193 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
166 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
173 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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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
52 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
57 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
3k 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 ...
0
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2answers
100 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
85 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
332 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
614 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
1k 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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390 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 ...