The Transport Control Protocol (TCP) is a low-level part of the protocol stack used by the Internet. It sits directly above the IP layer and is responsible for making sure that dropped packets are resent.

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How do I share stdout between multiple processes?

I want to receive live TCP stream, and make it readable by another processes at the same time, without saving it. For example, 111.222.233.244:1234 streams actual time. Server supports only one ...
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2answers
508 views

What ports are essential and should generally be allowed on a Linux system?

I'm running a desktop computer, but one with high threat risk. I've blocked all ports using a firewall except: HTTP, HTTPS, DNS, one port for torrent client. Do any common processes in distros ...
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1answer
3k views

Linux:How to tweak TSO and GSO from proc window / sysctl

OS:CentOS 5 I am doing some TCP optimization on my Linux box and want to put ON tcp segmentation offload and generic segmentation offload. I am doing it through ethtool Here is what I am doing: ...
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0answers
753 views

How to redirect/forward between a tun/tap device and a socket using linux tools?

I have a socks5 proxy that is bind to eth0. It opens two ports, Port1 is used to connect to remote (for example a http server), Port2 is to listen for clients to connect. Then I created a tun device. ...
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2answers
21k views

How to configure SVN/SSH with SSH on non standard port?

I have configured SSH to be on port 20000. When I try: svn co svn+ssh://server.com:20000/home/svn/proj1 proj1 --username jm I get svn: To better debug SSH connection problems, remove the -q ...
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2answers
544 views

I want a static IP address for my (network? or computer?)

Me and two friends have been making a video game. We've thought about download hosting a bit, but found that Mediafire, Box, and those sorts of file-hosting sites' maximum free file-upload size is far ...
4
votes
1answer
4k views

Run nmap via Tor

Is it possible to runnmap via Tor? When I googled around, I got the impression that Tor uses Polipo / Privoxy, which are socks5 proxies. So any TCP / UDP aware applications should be able to use them ...
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0answers
234 views

How to make Network alive but speed low, slow for upload, download?

I have own application written (Python, Java) which does upload/download for streaming. Now in my local office network and home network setup i can't simulate slow/low latency network (as a result i ...
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1answer
349 views

`cat /dev/ttyACM` loses data when piped through netcat

I'm reading data from /dev/ttyACM0 using cat /dev/ttyACM0 on a Raspberry Pi. The data comes from a device, which sends lines in the form 15.00 1316013 15 where the first number is a value, the ...
14
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1answer
3k views

Kernel socket structure and TCP_DIAG

I'm working on a software which connects to a Real Time data server (using TCP) and I have some connections dropping. My guess is that the clients do not read the data coming from the server fast ...
4
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1answer
4k views

What does net.ipv4.tcp_app_win do?

I can't figure out why do these variables coexist in Linux. The information from man tcp says (Ubuntu 12.04): For tcp_adv_win_scale: tcp_adv_win_scale (integer; default: 2; since Linux 2.4) ...
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1answer
139 views

How do I verify that the Linux kernel is not freezing when uploading or downloading large data over the ethernet interface?

How to verify if the Linux kernel is doing what it's saying for network interfaces? I have one network interface eth0 which has hardware support to do 1GB full-duplex. I have prepared 2 box. Now ...
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4answers
25k views

How does the server find out what client port to send to?

As I understand it this is what happens when a client makes a connection request: The server will be bound to a particular port number. The port number is always bound to a listening process. Since ...
6
votes
5answers
28k views

How can I tell if a TCP port is open or not? [closed]

I am trying to implement socket programming in C. When I try to connect from a client to a server (Ubuntu), it shows an error like "connection failed". So I think the problem is with the port. I am ...
5
votes
3answers
4k views

ssh will sporadically hang temporarily on fast connection

I am using Ubuntu 13.04 on my laptop, connected to my router at home. When working from home, I will ssh into the servers on campus, through a vpn, with X11 forwarding. ssh -X server.address.on....
23
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2answers
18k views

Performance of unix sockets vs TCP ports

For example on php-fpm: #listen = 127.0.0.1:9000 listen = /var/run/php-fpm/php-fpm.sock Is there any major performance differences between using unix socket-based listeners over TCP ports? (Not ...
3
votes
1answer
158 views

detect process that executes portscans

I have to administer an ubuntu 12.04 server, where there seem to go portscans to the whole subnet. How can I find out the process that does the scans? pstree init─┬─acpid ├─apache2───14*[apache2]...
3
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1answer
2k views

How to 'free' a TCP port?

I have some code that listens to a specific TCP port. However, when I stop this code and restart it quickly afterwards, I see the error ERROR: could not bind to socket on 0.0.0.0:7700 If I wait a ...
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0answers
253 views

No ports can be found using port scan

Problem: I have a laptop and a server (Home-Server) with fc17. They are both using the desktop environment. I am trying to set up a VNC server on Home-Server so that I can set everything up without ...
8
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2answers
10k views

Ephemeral port : What is it and what does it do?

I suddenly came across the term "ephemeral port" in a Linux article that I was reading, but the author did not mention what it is. What is an ephemeral port in UNIX?
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0answers
98 views

Why isn't hydra being disconnected?

I have SSHD running on port 5800 on some machine. (It is a my machine at home.) If I run this manually in a terminal: # ssh someIP -p 5800 The connection is lost because I am disconnected after 3 ...
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1answer
90 views

Enforce strict outbound ports (or ranges) for protocol

Is it possible to narrow the allowed range of outbound ports that can be used for a specific protocol (e.g. HTTP(S))? I understand that, by default, the system will randomly allocate any available ...
0
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1answer
2k views

How to connect to port immedeately, avoiding socket_bind(): unable to bind address?

When running a code that is supposed to read from a TCP/IP port I often get the following message (depending exactly what language have been used): socket_bind(): unable to bind address I know that ...
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0answers
65 views

Can we Bring Up eth1 after removing e1000e modules?

I am trying to setup TCP in RTnet. I am not sure whether its possible. I read that RTnet is not supporting TCP. Is that so? So now I am trying to setup rteth0 as server and eth1 as client. To setup ...
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1answer
3k views

Cannot create new service with xinetd in RHEL6

I've installed the Nagios on My RHEL 6.4(x64) machine. and i added one more module name called "NSCA" for some central monitoring solution.so the setup required add NSCA service detail under xinetd. ...
2
votes
1answer
448 views

iptables string not dropping packet from tcp streams while using conntrack and string

I'm facing an unusual issue where specific TCP steams are not getting dropped by iptables; instead it's like iptables is just removing those specific packets. We're getting the following traffic: x....
2
votes
1answer
117 views

Browser fails to reach any host on Solaris 8

I'm running Solaris 8 on a Sun Ultra 2 connected to a Verizon router. nslookup seems to work (it finds google.com) but the existing browser (Netscape 4.76 - yes - it's very old) fails to reach any web ...
0
votes
1answer
378 views

Read and parse XML input via TCP [closed]

I'm setting up something where I'll need to be able to setup a service that accepts input on a TCP port and then parses the XML provided and extracts the necessary data, then posts that to Google's ...
1
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0answers
93 views

configure allowed_tcp_congestion_control via config files in linux kernel

I am trying to come up with a custom set of TCP congestion control variants as part of the tcp_allowed_congestion_control. I do have multiple variants on my tcp_available_congestion_control list but ...
3
votes
3answers
730 views

Transfer a TCP connection from one Linux box to another behind NAT?

While experiencing an extremely slow download rate on one of my HTTP connections, I thought it'd be nice if I could just transfer the connection from my PC to an energy-saving home server that shares ...
3
votes
2answers
3k views

Is there a faster interface for info from /proc/net/tcp?

Given a linux TCP socket's inode (obtained via /proc/<pid>/fd), is there a faster way to look up the information that I can get from /proc/net/tcp about this socket? I have written a ...
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2answers
88 views

Is Port 13330 a standard-port?

I saw some programs using the port 13330. What is the meaning of this port? Is this port used by a special program?
3
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2answers
2k views

200ms latency between TCP send and tcpdump only with large messages

In our REHL server, latency between application send and tcpdump log is always very large for large messages, about 200 milliseconds (see below 697572-488690=208882 microseconds), whereas latency for ...
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3answers
5k views

rsh runs perfectly in normal user but not in root, very strange, why?

When I run command, rsh localhost pwd as a root It shows below output. connect to address 127.0.0.1 port 544: Connection refused Trying krb4 rsh... connect to address 127.0.0.1 port 544: Connection ...
3
votes
2answers
9k views

Checking if I can reach some ports from my computer

Is there a terminal command or something on OSX that I can use to test if I can reach some ports on a remote server? I know these ports are reachable on that server, because I can access them from ...
0
votes
1answer
147 views

What are the other congestion control algorithms specially designed for lossy Wireless Networks like LTE and WiMax?

I am trying different congestion control algorithms for getting maximum throughput and minimum delay across my setup for TCP flow.Please suggest other available algorithms apart from Veno, ...
2
votes
3answers
3k views

Linux Shell Script - Send command over TCP to Sharp Aquos

I'm writing a shell script that needs to send an 8 character string terminated with a x0d to a Sharp Aquos TV. An example is 'POWR1 \x0d' (POWR1 followed by three spaces and LF) The documentation ...
0
votes
3answers
816 views

How to send an email to myself on the same local machine (tcp port 25)

Does anyone know how to sent email to myself? I am trying to generate TCP traffic on port 25.
0
votes
1answer
940 views

How to display TCP handshake in Linux [closed]

Hi is there a way to display TCP handshake in Linux? Like for example this WIKI - TCP handshake Not exactly like the illustration but at least it would show client has sent SYN, ACK, FIN etc and the ...
3
votes
1answer
1k views

How to run Different congestion control algorithms in FEDORA 17 ..?

Earlier versions of Fedora has different loadable kernel modules which includes diffrent congestion control algorithms etc at (/lib/modules/"kernel-name"/kernel/ipv4).These are present in the form of ....
0
votes
2answers
679 views

Why my Http Proxy doesn't reply [SYN,ACK] after received a [SYN] packet from the client?

I have a http proxy running on Linux (RHEL 5.5), intermittently it doesn't reply [SYN,ACK] packet after received a [SYN] packet from the client. This issue can be recovered by restarting the proxy. I ...
2
votes
1answer
2k views

Why can't I use strace with rsh?

If I run rsh, it works, but prints some strange “Connection refused” messages at the beginning: $ rsh localhost pwd connect to address 127.0.0.1 port 544: Connection refused Trying krb4 rsh... ...
26
votes
1answer
862 views

Why does it take up to several minutes to clean a listening TCP port after a program dies?

If I kill a program that is listening on a TCP port, it takes up to several minutes until the port is reclaimed by the system and usable again. I've seen several Q/A mentioning this phenomenon, but ...
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vote
2answers
2k views

Why TCP TIME-WAIT State is present at both ends after a connection termination?

I am reading how the TCP states work and especially the connection termination part. All of the books or online material I read, shows that for the termination procedure these states are followed ...
12
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2answers
24k views

Getting current TCP connection count on a system

Instead of doing wc -l /proc/net/tcp, is there a faster way of doing it? I just need a total count of tcp connections.
1
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1answer
2k views

Default value for SO_RCVTIMEO option on Solaris

Is there any way to find out what is the default value set for option SO_RCVTIMEO on Solaris 10? If there is a way to find out how would one go about changing it? P.S. I am aware of ability of ...
2
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2answers
2k views

Port forwarding and masquerading

What is the relationship between port-forwarding and masquerading? If server A is configured to masquerade its clients, and client B accesses the Internet through server A, then since client B is ...
5
votes
2answers
128 views

Is it more dangerous to connect to the net as root?

If I make some kind of tcp connection to the net as root, is that less safe then making the same tcp connection as a normal user? I have been suspecting for a while that by making a connection as ...
2
votes
1answer
530 views

Running a local port scan and found open ports but, don't know what they're used for?

I wrote a very basic python script to port scan my system. I'm running linux-mint lisa: open_ports = [] for port in xrange(65536): conn = socket.socket(socket.AF_INET, socket.SOCK_STREAM) ...
3
votes
3answers
1k views

What process is sending TCP SYNs on Solaris 10?

Some process on my Solaris 10 machine is sending TCP SYNs to a remote machine. The remote machine never responds, so the connection is not established. How do I find out what process is initiating ...