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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Direct host SMB - Ports

It's well known that SMB uses port 445, and that NetBIOS uses ports 137-139. However, according to all official MS documentation (https://support.microsoft.com/en-us/kb/204279), SMB uses both TCP and ...
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2answers
691 views

How can I remap outgoing TCP ports?

Is there any way to remap a TCP port from a program were you not can change the port number? The program talks on port 4321 and I want it to go out on port 14321 on the local computer.
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TCP congestion control

I was curious to know which are the default TCP congestion control method used in latest version of MacOSx, linux kernal, windows 8, windows 7 and windows xp. Does it use newreno or anything newer?
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1answer
10 views

DrayTek Vigor 2830 open port issue

We're using a Vigor2830 for routing VoIP/SIP traffic. One of the ports required to be open is 5090 for TCP/UDP. Going into the open ports section of the Vigor menu we have opened all the ports ...
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2answers
837 views

Can IPSec (or any other VPN tunnel) hide your IP address while browsing?

Is there a VPN/tunnelling method which you can use to browse the web, but will also prevent somebody from seeing your IP address if they were sniffing the network? I wasn't sure if the IP address ...
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5answers
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How do IP answer packets reach their destination inside of a private LAN?

This is a little theory question that has been confusing me for a pretty long time. Basically, if we are inside of a private LAN, and we want incoming packets to reach, for example, an HTTP server ...
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2answers
81 views

Send TCP with incorrect checksums

I'm having trouble sending large files to an OpenStack machine. Our Internet connection is over LTE so bad packets are to be expected. However, even sending data over TCP results in corrupted data ...
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1answer
7 views

Reason for TCP Slow Start in Subsequent Connections

From my understanding TCP slow start is used to compensate and prevent congestion and loss. When a connection is successfully established and used for a while, the bandwidth of the TCP connection is ...
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0answers
6 views

pfSense does not close connections coming from LAN

I created a NAT rule that redirects external_ip:1234 of modem (pfSense itself) to 192.168.1.100:1234. I also wrote a server application which listens for connections on 192.168.1.100:1234. When I ...
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2answers
18 views

TCP: Disable pure ACKs?

I have a scenario where I wish to disable pure ACKs (TCP ACKs with no data), but I can't find how to do this. Is there an option that I can set so that ACKs are always piggybacked onto the next data ...
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1answer
20 views

Socat not closing tcp connection

I use socat 1.7.3.1-r0 and run following command on an alpine 3.3 linux server: socat -d -d -d PTY,link=/dev/ttyFOOBAR,echo=0,raw,unlink-close=0 TCP-LISTEN:7000,forever,reuseaddr Socat will listen ...
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1answer
11 views

Connecting from WAN to LAN

I'm developing an app for my family that uses sockets to comunicate between devices in LAN or WAN. As IP addresses change constantly I am planning an FTP server for address book and TCP/IP for ...
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0answers
339 views

Tunnelling TCP connection through NAT

My server is in my school's NAT and my desktop computer is in my home NAT. I want to SSH to my server from home. I normally used school's VPN, but recently for some reason I can't. So I'm looking for ...
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4answers
20k views

Subnet mask of 255.255.255.255

I have a subnet mask of 255.255.255.255.( Why is my subnet mask 255.255.255.255?). I refer that from the above question that it is as good as each computer is on its own network and cant interact with ...
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1answer
30 views

ping works but iperf3 doesn't show any traffic for TCP

machine A has IP (eth0: 192.168.1.1, eth1: 10.10.xxx.yy) machine B has IP (eth0: 192.168.1.2) A and B are connected through RJ5 on eth0, both sides. ping works fine on both side, but when running ...
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2answers
58 views

Why game latency fluctuates aggressively during day?

I play World of Warcraft (uses TCP) from India, on a server located in France. I get 180-200ms in-game past midnight which is quite comfortable for me, and unfortunately the best I can get due to the ...
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1answer
32 views

TCP RST Connection - Netflix - Only on Linux

I wouldn't have asked this here, but I am at wit's end, this makes absolutely no sense at this point. I have been trying everything. I have a single iptables rule: -A POSTROUTING -o eth0 -j ...
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0answers
21 views

How to add latency to TCP packets?

I have tried netem and wanem neither seem to be affecting the TCP packets. How can I add latency to TCP packets?
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1answer
34 views

RST sequence number and window size

RFC793 states the following about RST processing: In all states except SYN-SENT, all reset (RST) segments are validated by checking their SEQ-fields. A reset is valid if its sequence number is ...
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1answer
26 views

Can two different applications bind the same port on a host if they use different protocols?

 my question is quite clear I think. If two applications use different transport layer protocols (e.g. TCP and UDP or something else) can they open the same port number? How does the OS do the ...
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0answers
22 views

Duplicate and retransmission

Please help me understand why the receiver keeps sending duplicate acknowledgements, yet the senders keeps sending old packet sequence (re-transmitting of old packet seq) in the below capture: Please ...
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1answer
17 views

A bunch of tcp unseen segments and duplicates on wireshark?

Recently, my Mac has been unable to use the internet well. Even though it said my ping was between the ranges of 10-20 ms and my download speed was around 20 Mbps along with around a 10 Mbps upload ...
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0answers
14 views

tcp sesssion duplicate acknowledgement and retransmission

Please help in understanding why the receiver keeps sending duplicate acknowledgement yet the senders keeps sending old packet sequence (re transmitting of old packet seq)
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1answer
37 views

Close a TCP connection using nmap

I am trying to close connections in command line. For instance, I am trying to close my SSH connection with this Nmap command: $ sudo nmap -p 22 --scanflags RST <mySSHServerPublicIP> $ sudo ...
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45 views

Drop resilient tcp tunnel

I'm looking for a tcp tunnel that can provide connection drop resilient TCP connections to my VPS. Currently when I have some tool connected to my VPS and I switch from Wifi to LAN or my internet dies ...
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79 views

No connection could be made because the target machine actively refused it

On Windows machine, I start a server on port 62325 $ netsh firewall show state shows: Ports currently open on all network interfaces: Port Protocol Version Program ...
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1answer
77 views

Is it necessary for an RST packet to have an acknowledgement number?

I am studying about TCP reset attack. I know that some RST packets have an acknowledgement number (with the ACK bit set), and some RST packets do not have an acknowledgement number (the ...
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1answer
18 views

Acknowledgement number of an RST packet

This question states that the acknowledgement number of an RST packet should be 0, but I have found it to be other than 0 when I captured some HTTP packets using Wireshark. So when does the ...
2
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1answer
15 views

Can't get windows host file to forward HTTPS headers

I'm currently trying to write a proxy in C# using the host file to redirect requests (specific request). I only want it to intercept one address. It's on Windows and the proxy is run locally on the ...
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2answers
32 views

During queuing delay, do TCP, IP, and Data Link headers act as a packet or 3 different packets?

According to the definition from wikipedia, I found processing delay to be the delay caused by router processing the packet header. I am just wondering are TCP, IP, and Data link Headers all ...
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22 views

Still Lost on Blocking TCP Port Connections form Terminal

I'm still not 100% understanding what to do in Terminal to block certain URLs for specific ports. And I don't want to use Little Snitch. I really want to wrap my head around this. So if someone can ...
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2answers
33 views

what distinguished OSI from TCP/IP in practice?

so i am going through cisco ccent/ccna. working through the text on my own just for general useful knowledge. so in the early part of the book it goes into describing the different layers of the ...
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1answer
18 views

Where do I start to troubleshoot this strange activity from my firewall?

I noticed that my firewall yesterday blocked outgoing attempts starting at port 61494 and worked its way up to 62381, making a TCP outgoing attempt at each port once. The remote IP address seems ...
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TCP and UDP do not work with firewall

I can not connect my TCP-Client to my TCP-Server. Here is my Code: http://stackoverflow.com/questions/35661591/tcp-server-does-not-work-with-firewall I have already opened my TCP-Port "8888" in the ...
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2answers
36 views

Why ICMP is different that TCP and UDP? [closed]

what is the difference between Internet Control Messaging Protocol over Transmission Control Protocol and User Datagram Protocol
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1answer
1k views

How can I setup a Bluetooth device to serve web pages to a BT client via TCP/HTTP?

I'm thinking of making a linux-based Blueooth enabled device, which allows an external client (e.g. a laptop) to connect to it via TCP over Bluetooth and retrive web pages which allow it to interact ...
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3answers
6k views

Get the current/default value of TCP initcwnd on Linux

I can manipulate such value with: ip route change ... initcwnd 10 and then have a feedback with: ip route show But what about the default value before any modification? Is there a way to query ...
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1answer
48 views

Can HTTP deliver video over the internet or is that TCP?

The post below talks about delivering video content to users via HTTP. Is it confusing it with the TCP protocol? ...
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0answers
44 views

How to simulate TCP simultaneous open and close conditions?

I am learning TCP/IP protocol. I want to see simultaneous open, close, half open/close, etc conditions in practice. I have created simple TCP server and client program. How can I simulate simultaneous ...
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4answers
19k 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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1answer
746 views

Is ICMP port unreachable error generated by both TCP and UDP? [closed]

A program on machine X attempts to open a UDP connection to port 5376 on a machine Y, and a TCP connection to port 8632 on machine Z. However, there are no applications listening at the corresponding ...
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36 views

Is there a way to completely disable TCP keepalive?

I'm trying to disable TCP Keepalive in a linux machine. If I set the three keepalive parameters to 0, the machine refuses connections. sysctl net.ipv4.tcp_keepalive_time=0 sysctl ...
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Ubuntu IPTables

I started hosting my game-server on Ubuntu Linux 14.04 I am having an issues ، some enemies/bug abusers log in 2+ characters in the same second then they spam a certain spell/word that lags/stops my ...
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23 views

How to know that I passed the firewall from the TCP connections?

In my company, in order to access some intranet-sites, I have first to login to webpage (which I suppose is a firewall or something) with my account. If I login from FF for example, I can access the ...
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42 views

NAT doesn't allow TCP ACK for sent TCP SYN

We are using TCP Simultaneous Open for connecting TCP socket. Lets call one SideA and other SideB. From the wireshark log I see that first two SYN sent from SideB is blocked by SideA NAT. Then SideA ...
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1answer
501 views

make Xvfb listen only on local ip

to use graphical software even on my debian based systems without graphic cards (or in addition to its main graphic) i use the virtual frame buffer x server Xvfb. I am starting it with a little bash ...
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2answers
287 views

DNS Resolver for Windows over TCP

I know that DNS uses UDP with Port 53 for DNS queries. However, at my place sometimes UDP requests are blocked and DNS fails. I know that there is protocol for DNS over TCP and many public DNS servers ...
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2answers
41 views

How does a Router/Modem obtain the Port Number from an IP Datagram?

The IP datagram header is a layer below the TCP segment which contains information on the port. Therefore before a firewall can inspect a port number, must the IP datagrams be rebuilt into the TCP ...
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22 views

Wireshark FTP multiple ACK?

I'm trying to visualise somes frames that correspond to a file transfer between two machines on Wireshark. The thing is that there are multiple ACK for each FTP-DATA segment and I don't understand ...
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63 views

Replay captured TCP packets

I captured a tcp traffic using wireshark and saved the traffic in pcap file. I did two tests: Test 1: sudo tcprewrite --infile=capturedtraffic.pcap --outfile=temp.pcap ...