Stack Exchange Network

Stack Exchange network consists of 174 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

Questions tagged [tcp]

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.

0
votes
0answers
15 views

Tcp TCPBacklogDrop and packets pruned from receive queue

I am analyzing two virtual machines in the same LAN, tcp packet loss problem, but the knowledge has been exhausted. platform CentOS Linux release 7.2.1511 (Core) 3.10.0-327.el7.x86_64 #1 SMP Thu Nov ...
0
votes
1answer
25 views

possible packet loss

I have a program running on my local machine that prints data to port 50000. In a terminal on my local machine I run nc to connect to and print the data on the port. However, when using nc in terminal ...
9
votes
1answer
338 views

Which Unix-like system really provides the /dev/tcp special file?

I know /dev/tcp/<host>/<port> is a magic path handled specifically by some shells in redirections. But according to man bash: If the operating system on which bash is running provides ...
0
votes
0answers
18 views

Knockd disabled but it still intercepts packets [closed]

I set up knockd on latest Debian stable to enable pretty knocking but it didn't work reliably so I settled on doing it myself using just iptables. However, I couldn't get that to work using the exact ...
0
votes
1answer
41 views

Using socat to make a secure tcp connection to an irc server

Recently, I got into irc, so I installed sic and started - obviously - chatting. But, it turns out that sic doesn't provide any security features like SSL or TCP so I in man sic, they told to use ...
0
votes
1answer
77 views

How to Disable Ping ( TCP ) in Linux all the time? [closed]

I want to disable ping response all the time. I use the following command for disable ICMP ping iptables -A INPUT -p icmp --icmp-type echo-request -j DROP what should I do for disable TCP ping ?
2
votes
0answers
29 views

What happens to a TCP connection when the network is abruptly terminated

Say a user space application has a TCP connection with some non local endpoint. At some point, network gets abruptly broken (i.e. connection deleted in network manager, unplug the wifi dongle, cut the ...
0
votes
1answer
61 views

Delay between TCP send and actual write to the NIC

While looking for solution to a problem in socket programming with python described here (In short the problem is: I want my message(~ 25 Bytes) sent by a client over a TCP socket to be dispatched(...
0
votes
2answers
39 views

port 1556 listening on tcp6 causing issues

on my RedHat 7, i noticed that network connection for Netbackup stopped working and i tried everything including rurning off my firewall and disabled SELINUX with no luck. the only thing i noticed ...
0
votes
0answers
124 views

lsof shows protocol: TCP

I ran sudo lsof -p $(pidof foo) and I got a lot of these. Does anyone know what these represent? I know they come from the process but there are no ports / IP addresses. COMMAND PID USER FD ...
0
votes
0answers
19 views

nc shows partial output

I'm using busybox v1.28.1 on an embedded device (armv7l). I want to use nc to listen to TCP connections made by a javascript application (QML) on the same machine. Here an example of the request: ...
1
vote
0answers
88 views

Understanding how MobaXterm keeps an ssh connection alive

I want to have a stable ssh connection to a server where I do things. That would last for days or weeks. In general, one can set TCP keepalive to more than 7200 seconds: Socket reset by peer ever 2 ...
0
votes
1answer
44 views

Locally forward tcp port bidirectional

I wonder how it is possible to locally forward a tcp port, bidirectional, i. e. all packets leaving the local machine on port 25 (this port of course is actually dynamically assigned) should be ...
-1
votes
1answer
29 views

Restrict inbound access on localhost:TCP port

For reasons beyond my control, I have a binary that binds to TCP "localhost:$PORT". (Unix socket bindings would make this question moot). If I understand correctly, this means that although no ...
1
vote
0answers
41 views

Total socket count steadily increasing, tcp/udp sockets steady. Why?

I have a server (Ubuntu 16.04.5) running sockets.io and a few other things. This server is running about 5 or 6 different python apps and sockets.io. When the server reaches this level of ~6144 ...
1
vote
1answer
764 views

max no of tcp connections on a linux system

I know that /etc/security/limits.conf provides the persistent soft and hard limits for several values. However, in the relevant list there is no indication about imposed limits on: a) concurrent ...
0
votes
2answers
48 views

Telnet - how to verify why a port is blocked?

We have linux machines with RedHat 6.5 operating system. When we try to telnet to localhost on port 8182, we get connection refused: service iptables status Firewall is not running telnet localhost ...
0
votes
1answer
49 views

How to close one side of a TCP connection leaving other side hanging open? (No FIN or RST sent)

I am trying to recreate a scenario where a Solaris client is connected to a Linux server via TCP socket, but the client side of the connection suddenly goes down without sending sending a FIN or RST ...
1
vote
1answer
95 views

Deployment of haproxy between devices and Syslog server

Below is the current architecture of Syslog-NG to avoid single point of failure. Currently devices send same syslog message to two syslog servers listening on UDP port 514. Each server stores the ...
0
votes
1answer
52 views

nc getting stuck unexpectedly

I expected this: nc -l localhost 7000 </dev/null & nc localhost 7000 </etc/profile and this nc -l localhost 7000 </etc/profile & nc localhost 7000 </dev/null to finish after ...
0
votes
0answers
43 views

Why do we use sk_wmem_alloc in linux kernel?

I am analysing TCP kernel source code on kernel version 4.9.59 I learn about sk_wmem_queued variable thanking to refering to TCP-IP Architecture, Design and implementation in Linux book. From ...
0
votes
0answers
34 views

Executing a script after a TCP connection closes

I'm trying to figure out a way to execute a given script (a file) after a TCP connection closes, and if possible filter out the interface it was going through. Now, what i want to do with this data is ...
1
vote
0answers
35 views

Is is possible to disable TCP timestamping per-connection?

I am writing simple TCP/IP client (in python, later perhaps using ASIO or Qt) for an embedded system which rejects connections when the first SYN packet uses TCP timestamps. I can make it working by ...
0
votes
0answers
39 views

Load-balancing through multiple interfaces on the same server using Nginx

I'm testing proxy server with combination of Nginx TCP load balancing and SNI based HTTPS proxy. In my testing debian box I have following interfaces configured eth0 192.168.1.10 - proxy eth0:1 ...
1
vote
1answer
38 views

TCP variants under lsmod

I was reading about how TCP congestion variants are implemented in Linux. Each variant is implemented as a separate module. When I had read this question: Add TCP congestion control variant to Linux ...
0
votes
0answers
100 views

Transmission Control Block Size used in TCP

How can I find out the Transmission Control Block Size used in different Operating Systems, such as Linux and Mac OS?
0
votes
0answers
77 views

How to calculate packet loss ratio based on TCP segment?

I'm trying to calculate packet loss ratio to assess the quality of network based on 'netstat -s' command. My algorithm is below: step 1: send1 = the amount of 'segments send out' , retransmited1 = ...
1
vote
0answers
188 views

order of rules' processing in iptables chains [closed]

Isn't the order of processing the rules in iptables top to bottom? Given the following example; Chain DOCKER (2 references) target prot opt source destination RETURN ...
0
votes
0answers
140 views

TCP RST flag (windows vs linux)

I have broken client who I need to serv, and I can't change it or affect it in any way. I put same software serwer on windows and on linux. Windows is working, linux is not. After analyzing I figured ...
1
vote
1answer
325 views

How does MTR (run with TCP protocol) calculate the loss rate?

I thought TCP protocol itself will guarantee not to loose any bytes while connecting. About this viewpoint, please refer to https://stackoverflow.com/questions/23841896/will-tcp-connection-lose-...
0
votes
1answer
283 views

How to find the cause of TCP RST on Linux (Ubuntu Server)

In my mail server I'm getting high TCP reset send between working hours, as shown in this grafic: This is a capture of the server traffic filter by tcp-rst: When I run "netstat -i" I get this: ...
1
vote
2answers
190 views

Send TCP packet to the same source [closed]

I want to design a system which reduce travel time of packet what is happening in reality is I send a SYN bit from client side, this bit travel through router then to server and server reply SYN+ACK ...
1
vote
3answers
142 views

Is it possible to spoof a successful TCP connection with iptables?

Typically with IP tables you would either drop or reject traffic. For TCP is there a way to have iptables instead send a syn back but forget the connection?
0
votes
0answers
72 views

Different behavior between kernel 4.8 and 4.10 when receives the SYN packet

I have two Linux servers. server A: 4.8 server B: 4.10 There is a socket running on each server and listen at port 9999 with concurrent request limit as 1. When all concurrent request threads of A ...
2
votes
1answer
219 views

How to change TCP congestion control algorithm on OpenBSD?

On FreeBSD, I can change the TCP congestion control algorithm via net.inet.tcp.cc.algorithm. On OpenBSD, there is no net.inet.tcp.cc.algorithm parameter. So, here is the question: How to change TCP ...
0
votes
1answer
375 views

Get IP address of socket used by process

given a process Id (that use sockets), I would like to get the IP on socket endpoints. e.g When new SSH session is created, the sshd demon fork process per session. I want to get the IP endpoints ...
-1
votes
1answer
47 views

How to open up a tcp server compatible with tcpgoon

I have tcpgoon installed on one computer, provided that there is a direct VLAN connection, how do I create a TCP server on my second computer?
2
votes
1answer
36 views

How can I be sure that an application is running on same cpu/core that its TCP send flow is?

Let's suppose the following (very simplified egress tcp queuing) flow: -->[app (nginx)] -->[send_buffer(tcp_wmem)] -->(qdisc txqueuelen) -->[ring buffer(tx_rx)] -->(dma) -->[...
1
vote
1answer
280 views

connect to server with netcat and receive *multiple* files with one request/connection

Say I have an http or tcp server running, which serves tarballs (.tgz files). Is there some way I can receive files individually so I can do something like this: nc localhost 5000 | how can I read ...
2
votes
1answer
175 views

How do I make ppp reliable over lossy radio modems using pppd and tcp kernel settings on debian?

I am having a lot of trouble establishing a reliable ppp / tcpip link between two debian systems over radio modems. My hardware topology is a little complex. The system uses: Raspberry Pi 3B at ...
1
vote
2answers
803 views

How can I detect if telnet is running on a server?

I have a digital scope, with LAN connection. I'd like to check if telnet is running on the scope (the manual doesn't say so, but then the manual doesn't offer anything useful about the LAN port). I ...
0
votes
0answers
287 views

Send response based on netcat client request

I am trying to create a socket where the client receives a response based on their request, but I can not figure out how to achieve this on CentOS 7. Until now I have the socket opened on port 100 ...
0
votes
1answer
36 views

How can I run this tcp command in Ubuntu? [closed]

I want to run this command in Ubuntu: tcp 0 0 0.0.0.0:50010 0.0.0.0:* LISTEN <pid>/java but tcp is not recognized in Ubuntu. What could be an alternative for this?
0
votes
0answers
58 views

mtu 9000 issues only on tcp and not icmp possible?

I have a connection between two datacenters and rsync between them stalls often. I think it is related to the mtu 9000 (I actualy set it to 8900 because of some possible vlan use) I have the ...
0
votes
1answer
78 views

Using bash for tcp connections

In order to redirect the tcp connections with bash, why the following commands return nothing? [root@rocks7 ~]# echo -e "GET / HTTP/1.1\n\n" > /dev/tcp/yahoo.com/80 [root@rocks7 ~]# printf "GET / ...
0
votes
1answer
38 views

How is data transfer initiated in TCP?

Conceptually, I think of a TCP connection as having two aspects. The "connection" - i.e. an arrangement where the two hosts "agree" to commnunicate with each other. loosely analogous to calling ...
1
vote
1answer
267 views

Read and write to same netcat tcp connection

I have this pipeline: ( tail -f ${named_pipe} | nc localhost ${port} | ql_conditional_release &> "$HOME/debug.log" & disown; ) &> /dev/null so I am reading from the netcat ...
2
votes
2answers
46 views

Distinct network subnet masks

I understand that 192.168.1.0/24 & 10.0.0.0/24 are distinct networks however are the following also distinct networks? 10.0.0.0/24 & 10.0.8.0/24 10.0.0.0/8 & 10.0.8.0/24 I have a LAN ...
0
votes
0answers
68 views

spurious TCP reset with IP id 0 from linux based forwarder

I am trying to debug an issue with spurious TCP reset being sent by a linux based device that forward traffic from one interface to another after doing a NAT. The setup is something like this client -...
3
votes
2answers
50 views

how to make a secure local port as a normal user

I am working on a shared linux server as a normal user with no root access. Can I start a program listening on a local tcp port, and be the only user able to connect to that port? I can control the ...