0
votes
1answer
25 views

How to add code into the linux kernel?

I am studying how to analyse and evaluate the TCP/IP protocol stack of Linux. My goal is to study the performance of the tcp/ip protocol stack as a whole, to study the time cost of each layer and ...
0
votes
0answers
13 views

How to use netperf on specific NIC port?

I have two servers, SERVER and CLIENT and each server has its own onboard 1 GbE ports, and its own NIC with a 10 GbE port. SERVER and CLIENT are interconnected on both a 1 GbE switch (administrative ...
0
votes
0answers
47 views

How to send message to virtual serial port created with socat?

I am using socat to create a virtual serial port on linux socat -d -d PTY,raw,echo=0,link=/dev/ttyVA00 PTY,raw,echo=0,link=/dev/ttyVB00 which prints socat[31640] N PTY is /dev/pts/2 socat[31640] N ...
0
votes
0answers
6 views

Setting/clearing packet's TCP flags with iptables

I know iptables can match packets with certain TCP flags using --tcp-flags. But how do I set or clear some flags on a matched IPv4 packet?
1
vote
0answers
36 views

Delete Hung TCP Sessions with SNMP

What I am trying to do, and failing horribly, is to close a TCP connection... I am trying to do this via SNMP and the functionality that is provided in the TCP MIB. First, I look at all the ...
1
vote
0answers
55 views

No response received from github ssh randomly

My git pull started to stop working randomly with this error $ git pull ssh: connect to host github.com port 22: Connection timed out fatal: The remote end hung up unexpectedly I tried debugging ...
1
vote
0answers
81 views

TCP/IP resets (Linux, SSH, RDP, ADSL router)

I have an ADSL router (model Pirelli DR A226G) that seems to cause dropped tcp/ip connections (not ADSL connection per se). I have tracked it using Wireshark and captured a few cases and they always ...
1
vote
1answer
42 views

How to configure the physical machine and virtual machine?

If I want to transfer data between the physical machine (windows operating system) and virtual machine (Linux real time operating system). Could anyone please explain about configuring the data ...
0
votes
0answers
23 views

Switching ethernet interfaces in Fedora

I am working on a computer which has two gigabit ethernet interfaces. This is the current configuration: PORT 1 (INTERNET) PORT 2 (SPP) Port 1 connects my computer to the internet whereas ...
0
votes
0answers
326 views

connect to a serial device via TCP socket

My setup is this: serial device ttyUSB0 connected to laptop A software that opens TCP socket to listen and write to, also runs on laptop A (linux) My goal is to pipe data from/to serial device ...
0
votes
1answer
187 views

How can I detect long-lived connections and mark them for shaping

I would like to detect TCP connections which have been open for more than one minute (or for greater than N bytes, or M packets), so I can classify them as bulk traffic ("downloads") and de-prioritise ...
0
votes
0answers
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 ...
0
votes
2answers
143 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 ...
0
votes
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 ...
1
vote
1answer
824 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 ...
3
votes
3answers
1k 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 ...
0
votes
1answer
521 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 ...
0
votes
1answer
136 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 ...
3
votes
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. ...
2
votes
2answers
2k 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 ...
3
votes
1answer
155 views

Maximum TCP session time on Linux

I have two python scripts, which reside on different machines and are connected by a TCP connection. If the scripts do not share any data, they send dummy packets, so that the session is never idle ...
2
votes
1answer
148 views

terminal tools and logs for debugging TCP issues

I have a server which I am testing for functionality (not load, not stress) with tsung. 50 users / second, 100 total users. Judging from tsung (tsung is the testing framework) graphs, there TCP ...
0
votes
1answer
100 views

What is the difference between :::: and 0.0.0.0 from the netstat -an output?

I just want to understand the difference between :::: and 0.0.0.0. I believe both are same which let connection from outside if any processor is listening to that port. udp 0 0 ...
8
votes
2answers
528 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 ...
0
votes
1answer
106 views

How to log selected tcp packet

I am troubleshooting a problem where a long TCP transaction (>=60s) would disconnect between my source (Point A) and destination (Point B), whilst passing through an internal Linux Gateway and several ...
0
votes
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 ...
7
votes
6answers
3k 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 ...
1
vote
1answer
486 views

Connection stays alive but endpoint is dead?

Does anyone have an idea what would cause a TCP connection (client side) to stay in the ESTABLISHED state for about 24 hours, even though the server was restarted? The client process stays on the ...
2
votes
1answer
290 views

Why is my tcp window size going to zero when using VIM over VPN

I use a mac os laptop over a typical (i.e. crappy) wireless home network and connect to work over a VPN. I ssh into the linux (ubuntu) desktop I have in my office at work. (When I say, "I ssh": I ...
10
votes
2answers
3k views

On the Performance of TCP implementations of Linux and Windows

As 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 ...
3
votes
2answers
3k views

Kill established tcp connection on Linux

How can you kill an established TCP connection on Linux?
2
votes
4answers
1k views

Linux Command Line Tools for Analyzing OS + NIC TCP Latency

I'm hoping to find an existing Linux tool for measuring latency: I'm trying to diagnose how much latency my OS and NIC card are adding to TCP latency in Linux. I looked at the following tools but ...
1
vote
1answer
1k views

Can't access HTTP server, but ping works in LAN

I encounter a problem when configure the connection. My computer resides in a LAN, I want to assign it a static IP address. Thus with the help of port mapping on the router, I will be able to access ...
3
votes
1answer
350 views

Why small TCP connections succeeds, but big ones fails?

Sometimes from Linux system I see the following weird behaviour: I able to ping things and sometimes use some services, but networking is very bad. For example, now I routed connection through my ...
3
votes
2answers
4k 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 ...
3
votes
3answers
149 views

Distinct Proxying for any TCP-related Protocol

I'm not sure what to call it (proxy/redirection/relay), and I am hoping some software or solution possibly exists for linux. My intention is to be able to listen on a single public facing ip:port ...
2
votes
2answers
4k 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 ...
3
votes
3answers
366 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?
0
votes
2answers
198 views

tcptraceroute showing paths of greatly varying length

I'm tracing a path to my server using tcptraceroute. The server is showing intermittent network availability. It's as if some packets get through fine, others take a long time and some never get ...
1
vote
2answers
1k views

Count exchanged bytes per TCP connection

I need to get a table updated with the exchanged bytes (Rx and/or Tx) for each ESTABLISHED TCP connection on a linux machine (well, at least, a list of connections (port ranges), thus not actually ...
4
votes
1answer
6k 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 ...
1
vote
1answer
790 views

What does netstat mean by “acknowledgments not containing data received”?

Netstat reports some TCP packets in the following category acknowledgments not containing data received. However, I'm not clear what this phrase means. Goggling and the netstat documentation don't ...
0
votes
1answer
49 views

Which element of network refused connection

How could I determine, which element of the network actually refused/closed the connection?
0
votes
2answers
568 views

Finding all processes that are using a given port [duplicate]

Possible Duplicate: Finding the process that is using a certain port in Linux More specifically, how can I find out what processes are using port 8080 (for example a web server)?
1
vote
2answers
1k views

Manually forcing TCP connection to retry

I have a TCP connection (SSH session to some computer for example) Network suddenly goes down and drops all packets (disconnected cable, out of range). TCP resends packets again and again, retrying ...
1
vote
3answers
1k views

Tcp Port Open by Unknown Service

Running openSUSE 11.2 x86_64. Here's what a nmap of my IP provides: PORT STATE SERVICE 23/tcp open telnet 80/tcp open http 2800/tcp open unknown 8008/tcp open http I would like ...
3
votes
6answers
2k views

(linux) tool to monitor “quality” of tcp connection?

I am looking for a tool to monitor the quality of a TCP connection. I am trying to describe what I mean: It should be a tool with a client and a server part. The client sends, say, 1kB of data per ...