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.

learn more… | top users | synonyms

97
votes
14answers
10k views

Must TCP use IP?

Is it true that TCP is short for TCP/IP and they mean the same thing? Is it possible for TCP to be built on top of another protocol besides IP?
38
votes
2answers
15k views

How does Router know where to forward packet

If several computers with local addresses (192.168.0.#) are connected to a router and each computer opens a web browser and requests a page over HTTP, when these TCP:80 packets are sent out, the ...
36
votes
4answers
72k views

What does “On-link” mean on the result of “route print” command?

I'm using Windows 7. When I type "route print" under command prompt, I get a IPv4 Route Table with several "On-link" values under the Gateway column. For example, like this one: IPv4 Route Table ...
32
votes
1answer
3k views

What happens to TCP connections when I remove the ethernet cable?

For a TCP connection, when I remove the cable and reconnect after 30-40 seconds there is no packet loss issues. But when the reconnect time is more than a few minutes all the packets are lost. I know ...
29
votes
15answers
74k views

How do I kill a process that is dead but listening?

I'm developing an app that listens on port 3000. Apparently there's an instance of it still listening to the port because whenever I start it, it can't create a listener (C#, TcpListener, but that's ...
25
votes
4answers
4k views

How does HTTP become stateless?

HTTP is said to be stateless. Meaning, it doesn’t need to store information for the transmission of data. But HTTP uses TCP, which is state oriented. If that's the case, how does HTTP becomes ...
20
votes
5answers
14k views

Ethernet vs TCP vs IP?

What is the difference between Ethernet, TCP, and IP in simple (simple abstract) terms? Please do not copy from Wikipedia...
20
votes
7answers
26k views

Why is it bad to have open ports?

Here's something that has always baffled me. Why is it bad to have open ports on your computer? Assuming you don't have a virus on your computer or some other program listening to a port that may ...
19
votes
2answers
33k views

For what does ssh use UDP?

Wile doing research I noticed that SSH both uses TCP and UDP. I completely understand the use of TCP, but UDP seems a bit strange. Why would I use an "unreliable" transport protocol with minimal ...
16
votes
3answers
2k views

Does the sequence number of TCP packet headers wrap around?

I was wondering, since the sequence number in a TCP header field is randomly chosen during the handshake and is gradually incremented as packets are exchanged, what happens after 2^32 - initial_seq_no ...
12
votes
5answers
17k views

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 ...
12
votes
2answers
6k views

Do browsers create new TCP connections for each HTTP requests?

So I know that HTTP is basically just a text protocol over TCP, and that TCP is state / connection based. That means that the browser has to connect over TCP to a server before doing an HTTP request. ...
11
votes
1answer
16k views

Is there a hard limit of 65536 open TCP connections per IP address on linux?

Is there a hard limit of 65536 open TCP connections per IP address on linux? I read somewhere that there was, but someone is asking for confirmation and i just can't find it. I seem to remember it ...
11
votes
2answers
7k views

On the Performance of TCP implementations of Linux and Windows

I understand the implementation of TCP stack in windows and Linux are different. Windows uses a congestion control algorithm known as the TCP Reno while Linux uses Cubic. How do the 2 protocols ...
11
votes
2answers
13k views

How does circumventing IP restrictions through DNS work in the case of hulu.com?

I just heard from an australian guy that it is possible to watch hulu.com from Australia (which is actually restricted by country IP checks) by using certain DNS servers. Now I was wondering, how ...
10
votes
3answers
2k views

What do the numbers used in a IPV6 address mean?

I am trying to understand IPV6. I have a server with the following IPV6 address: 2607:f750:0:3f::f59. I don't understand what the numbers mean. It looks totally different from an IPV4 address. ...
10
votes
5answers
81k views

Open a test TCP connection to a specified IP/Port

I'm looking for a tool that works across windows (xp through 7) that will allow me to open a TCP connection to a specified ip and port. This functionality used to exist in windows xp (netsh diag ...
10
votes
1answer
7k views

Why Windows 7 / PuTTY drop TCP connections even on very brief outages?

I have a small local network that piggybacks on a captive WiFi, and I use ssh on OS X with -oServerAliveInterval=240 and PuTTY 0.62 on Windows 7 Professional for establishing connections to my Linode, ...
9
votes
5answers
881 views

What ports are used by an application [duplicate]

I'm testing an application which opens its own ports (acts as a server for these ports, hence listens at that ports) and where the same application connects to ports bound by other applications (acts ...
9
votes
4answers
18k views

What's the minimum size of a TCP packet

A post here: http://blogs.adobe.com/dreamweaver/2011/02/optimal-css-tiled-background-image-size.html staes that "The smallest download that browsers can do is 1K bytes." Is this due to minimum size ...
9
votes
4answers
10k views

Why is multi thread downloading faster than single thread?

There is one large file in my server. I find that multi thread download can get 20Mbs, but single thread can get 10Mbps, can anyone explain this?
9
votes
6answers
8k views

Port scan revealed port 1111 open. What is it?

I am new to systems administration and have a new server running a website with http (at port 80), https (at port 443) and ssh (at port 22). I did an nmap port scan using my personal laptop and other ...
9
votes
2answers
1k 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 ...
8
votes
2answers
1k views

Puzzling TCP performance over 3G / UMTS

I'm using 3G as my primary internet connection, and TCP over this thing is getting more puzzling every day. For example: Downloading from kernel.org is crazy fast: $wget ...
7
votes
5answers
2k views

How does a server get notified about the HTTP request?

I have a basic understanding of how HTTP works. I understand the client (web browser) makes a request and server responds back to the request. However, the thing I don't understand is how does a web ...
7
votes
2answers
28k views

what is type of ICMP packets? TCP or UDP

ping packets is a type of ICMP packets.Is there any relation between ICMP with TCP.In other can we guaranty their arrival in the network I want to know ICMP packets in the network is tcp or udp or ...
7
votes
2answers
19k views

How can I see 127.0.0.1 traffic on Windows using Wireshark?

Every time I try to filter to just show a specific IP address, I get an error indicating that it is "not an interface or a field." I have no idea what that means. Furthermore, I don’t really see any ...
6
votes
4answers
20k 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?
6
votes
4answers
16k 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?
6
votes
1answer
4k views

In TCPView, why does the svchost.exe process need to listen on so many TCP and UDP ports

Looking at TCPView I can see over 25 svchost processes using TCP and UDP ports. If these svchost processes are the various services required by Windows, then why would so many be using the network?
6
votes
1answer
815 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 ...
6
votes
3answers
15k 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 ...
5
votes
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 ...
5
votes
1answer
619 views

Does TCP/UDP send file sequentially or randomnly?

Does TCP/UDP protocol always send or receive file packets sequentially? Would it possible to make a choice which data packets will be sent first using sockets API?
5
votes
1answer
3k views

What's up with port 8080 on my OSX box?

I thought a web server process I brought up was listening on localhost:8080, and tried to connect to it, but kept getting connection reset errors. As it turns out, I was mistaken and my process was ...
5
votes
2answers
6k views

Redirect serial com to tcp port

I would like to know if exists some utility that connects to serial port and redirect input and output to a tcp port. I need this for a Java application, I need to write and read to a serial port but ...
5
votes
1answer
9k views

Is there a half-open TCP connection limit in Win 7?

Or at least, is it a low limit like 10 or 50? It was present since XP SP2 (I think), and was finally cancelled (= I think now the user can set the limit manually) in Vista SP2. What is the current ...
5
votes
3answers
3k views

Good process specific packet sniffer / viewer?

I am looking for a good, free or not free, packet sniffer. The main feature I am looking for is an ability to watch a chosen process and view / read all of the data it is sending or receving. Also I ...
5
votes
1answer
319 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 ...
5
votes
3answers
9k views

Cannot connect to guest OS from host OS

I have installed OpenSUSE on VMWare player as guest OS and my host OS is Windows XP. What I want to achieve is to send message from my host (i.e XP), say on port 7000 and receive it on a specific port ...
5
votes
1answer
326 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 ...
4
votes
3answers
2k views

How to force a process transmit over UDP instead of TCP?

I 'm running an ffserver process on a Linux machine, in order to achieve video streaming via ffmpeg. However, there is a delay on video streaming. On ffserver configuration file I define Port 8090. ...
4
votes
9answers
3k 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 ...
4
votes
1answer
3k views

What is the purpose of ports?

I have a few questions in regard to the following explanation of ports I found. The Application layer talks to the Transport layer through a port. Ports are numbered and standard ...
4
votes
2answers
9k views

How to make tcpdump (or other tool) to actually dump TCP stream?

I expect something like this: $ nc example.com 80 GET / HTTP/1.0 HTTP/1.0 500 K.O. Content-Type: application/null Content-Length: -1 $ Meanwhile: # tcpdump -i eth0 --actually-dump-all-tcp ...
4
votes
2answers
2k views

How to manually do a TCP handshake

Telnet can be used to manually do things that programs do automatically. When I connect to a server I noticed that it automatically does the 3-way handshake to establish a TCP connection. Can it be ...
4
votes
3answers
5k views

How to use DNS over TCP?

Google DNS (8.8.8.8 and 8.8.4.4) are blocked (or polluted) by all ISPs available to me (and DNS by ISPs just return wrong answers for some sensitive sites!!), and it is said that if we change DNS from ...
4
votes
1answer
8k 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 ...
4
votes
2answers
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 ...
4
votes
1answer
353 views

Why does writing IP addresses this alternate way work, and is there a practical use case for it? [duplicate]

Recently I saw an incorrectly typed telnet command, and I saw that "regular" numbers were interpreted to IP addresses. I tried this myself in Windows and the same behavior is shown there, so obviously ...