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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Why does reading /proc/net/tcp take a long time ss is quick to return the same sort of data about the connections table?

On Linux 2.6.32, if you read (for example, cat) /proc/net/tcp, on a very loaded system (for example, a web server), you will find that reading 100K entries takes over 30 seconds. That's a long time. ...
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1answer
28 views

Iptables Help redirecting specific TCP/UDP Ports to VPN (tun1)

So I have a linux based router and have a vpn client set up to route traffic through the vpn and isp per iptables commands i am attempting to route specific tcp and all udp ports through the vpn only ...
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0answers
636 views

Improving TCP performance over a gigabit network

I have two machines both network cards speed is 10Gbps. The inbound bandwidth between the two machines is 10Gbps, the outbound bandwidth internet bandwidth is 500Mpbs. Both machines are using public ...
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2answers
3k views

Redirect the default HTTP port to an application

On my CentOS server at mydomain.com, I have an svn web application running on port 8880. I want to hide the port: at this moment, if anybody wants to access, they need to access through http://...
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2answers
81k views

how to connect ssh 'with' specified port?

I know how to connect 'to' a certain port when ssh'ing. ssh user@remotehostip -p XXX but is there a way to establish a ssh 'with' a certain port? I mean, is there a way to specify the port which ...
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0answers
20 views

Port netcat request info to bash script

I have this super simple TCP server that takes requests and returns the output of handler.sh: #!/bin/bash while true ; do nc -l -p 1234 -e handler.sh; done I'd like to port the requested path to ...
4
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1answer
1k views

How to investigate a random reset on TCP client port connected via loopback interface to a server

I have a test suite which initializes a server on the localhost and then runs thousands of stress tests which include starting and stopping clients connecting to this local server on same machine. I ...
15
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1answer
746 views

How to terminate a TCP connection established by bash itself?

I have used exec 3<>/dev/tcp/192.168.0.101/6435 to establish a TCP connection with 192.168.0.101:6435. And I have received as well as sent a few messages with the pipe command. Now, I want to ...
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5answers
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Simple way to create a tunnel from one local port to another?

I have a development server, which is only accessible from 127.0.0.1:8000, not 192.168.1.x:8000. As a quick hack, is there a way to set up something to listen on another port (say, 8001) so that from ...
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1answer
35 views

TCP over TUN: SYN/ACK is received, but no ACK is generated, and socket remains in SYN_SENT state

I am tunneling an outgoing TCP connection over a TUN interface set up by a program I wrote. The TUN interface basically just relays the packets to/from a proxy server, with minimal modifications (...
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1answer
237 views

does NFS overrides TCP keepalive time?

NFS server somehow disconnect NFS client detect server is disconnected client tries to reconnect server reappears and reconnect successfully it seems that TCP keepalive, connection timeout is ...
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28 views

Cannot telnet outside network to open port on OEL 6 machine

I have an OEL 6 server that locally is assigned IP 10.200.15.79. It is hosting a business application that uses port 1031 to send and receive information through TCP/IP. To allow this on the OEL ...
2
votes
1answer
49 views

Transfer Size limit for SCP, SFTP, RSYNC?

Is there a maximum size limit to the size of collective size of the files that are to be transferred in one go for the above protocol. My intent is to know if for example after 1 GB any of these ...
3
votes
2answers
8k views

How do I find out what file Apache is serving when a port is hit?

I'm working on a server someone else set up. The server is CentOS 4.6 running Apache/2.0.59 (httpd). They have an update service setup on port 8443. I know it is working but I need to find out what ...
2
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0answers
51 views

Why would all our CLOSE_WAIT connections have 24 bytes in the receive queue?

We have an Apache reverse proxy that is having connectivity issues with the back-end. This results in timeout errors such as this: [Thu Apr 21 12:12:26.031207 2016] [proxy_http:error] [pid 64620:tid ...
3
votes
1answer
45 views

How do I configure Docker containers to have unique IP addresses that are not the default ones?

How do I configure Docker containers to have unique IP addresses that are not the default ones? The Docker containers will run Apache or some web service. These Docker containers will share one host ...
1
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1answer
24 views

How do I configure VirtualBox snapshots running server processes to restore correctly?

I'm running VirtualBox 5.0.20 on an OS X host. There's a variety of guest systems, including Ubuntu, CentOS, Windows and OS X. For each of these systems, I created a live snapshot (i.e. while the VM ...
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3answers
10k views

Is it possible to connect to TCP port 0?

Listening to TCP port 0 allocates me a free port number on the system. But what happens when I try to connect to TCP port 0? The obvious answer is: "It doesn't work": $ nc localhost 0 ...
2
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1answer
32 views

Can you send a TCP packet with RST flag set using IPTABLES as a way to trick NMAP into thinking a port is closed?

I am learning Nmap and a thought occurred to me with regards to a SYN scan... A SYN scan sends an empty TCP packet with the SYN flag set to illicit a response from the target of either RST, ...
0
votes
1answer
65 views

SSH connection giving Connection refused error

I am using CentOs. I can SSH from local machine to server A. I can also SSH from local machine to server B. But I cannot SSH from server A to server B: $ ssh -p <portB> root@B root@B's ...
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0answers
68 views

How do I get Consul to work so I can get Docker Overlay to work?

I am running CentOS 7 with Docker. I am trying to install Consul on the Docker server. Consul is unzipped. The binary file works for showing the version. I ran this: echo $CONSUL_RPC_ADDR This ...
0
votes
1answer
50 views

netcat daemon for calling functions in sh script

I'm new to shell programming and I have created a script that opens a connection to a server of mine. I want to have this script listen for an input from a client node and use that to run a function. ...
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0answers
31 views

What does TCPRcvCoalesce, TCPAutoCorking and TCPHystartTrainCwnd in netstat mean?

We have some RHEL7 Apache reverse proxies that experienced a performance degradation event. After a few hours, restarting Apache restored performance to normal levels. We are trying to determine the ...
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2answers
72 views

Add TCP congestion control variant to Linux Ubuntu

I want to test different variants of TCP in Linux Ubuntu. I have Ubuntu 14.04 LTS with Kernel version 3.14. When I check the available congestion control algorithm using the following command sysctl ...
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1answer
35 views

log script output to file and terminal at the same time

I have a simple tcpnotification receiver script that logs notifications. At first I just printed the notifications in terminal but then changed script so that notifications are logged in a file. But ...
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1answer
52 views

Connecting to server on localhost with same source and destination port

Here is simple server listening to port 80 of localhost: nc -4 --listen 127.0.0.1 80 Here is the client to connect to server on localhost using source port same as destination port of server: nc -4 ...
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0answers
38 views

why does nmap shows same ports sometimes as filtered and sometimes as closed?

When I'm scanning port range 4050-4060 of an smart metering device all ports are reported as closed: root@abc:~/rvm/dlms# nmap -p 4050-4060 192.168.1.242 Starting Nmap 6.47 ( http://nmap.org ) at ...
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1answer
63 views

Bash reading from /dev/tcp, without external binaries

I'm trying to read files with bash tcp socket, So on one host I do, nc -l 8888 < /etc/passwd And on another machine, echo </dev/tcp/127.0.0.1/8888 But it didn't read the file as expected, ...
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0answers
16 views

Several TCP Window Scale values depending on interface?

Is it possible that TCP Window Scale value set by default on a socket (not raw) depends on the interface used? Where are these values stored?
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0answers
77 views

TCP SYN,ACK Retransmissions

The following network trace was recorded on a Raspberry PI running Debian Linux. It seems the Raspberry is not seeing the data packet #36995 for some reason; it is just stupidly repeating his SYN,ACK ...
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1answer
104 views

How to pass received data from netcat to another script as argument?

I have simple bash nc script: #!/bin/bash nc -k -l 127.0.0.1 4444 > filename.out which listens 4444 port for TCP connection. Instead of redirecting received data to filename.out I would like, if ...
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2answers
41 views

Count Bytes by Ports

Using RHEL/CentOS 6.7 -- I want to be be able to know byte counts on IPv4 ports. We have thousands.. I would think counting via IP Tables for that would be a bit unweldy and slow the firewall a wee ...
0
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1answer
46 views

reading the output of netstat for tcp

If I ssh root@server -R 5901:localhost:5900 and netstat -an I get: Active Internet connections (servers and established) │ Proto Recv-Q Send-Q Local Address ...
2
votes
1answer
268 views

socat/netcat UDP to TCP

I am trying to bridge a connection between UDP and TCP. The UDP - must listen on port. The TCP - must connect to a server. The purpose of the connection is to control VLC player. I tried netcat and ...
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0answers
110 views

Apache Load Balancer Timeout

We have two httpd servers running on RHEL 6 behind a hardware load balancer We are getting timeout errors in our httpd error log. [Fri Feb 19 15:06:49.823372 2016] [proxy_http:error] [pid 15760] (...
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votes
4answers
8k views

Can TCP provide more than 65535 ports?

Is it possible to setup a Linux system so that it provides more than 65,535 ports? The intent would be to have more than 65k daemons listening on a given system. Clearly there are ports being used ...
0
votes
1answer
154 views

Lots of TIME_WAIT in netstat on apache server

What would be the reason for many TIME_WAIT here? Even we have very few ESTABLISHED, SYN connection. [root@www ~]# netstat -natp | grep "210.XX.XX.XX:80" | awk '{print $6}' | sort | uniq -c 1 ...
0
votes
1answer
51 views

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 ...
15
votes
5answers
67k views

How to check whether firewall opened for a port but not listening on the port

We will be deploying a new application to a Server and the application will be listening on port 8443. We have asked Network team to open the firewall for the port 8443 on that server before deploying ...
2
votes
0answers
41 views

Netid in ss output is confusing

I'm on an Ubuntu 14.04 x64 machine. I have something running on port 51236 and I want to know whether it's TCP or UDP. So I ran ss -an | grep 51236 and got the following output. tcp ESTAB ...
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0answers
161 views

Half-close netcat connection

How can I have a netcat connection terminate the sending half of a TCP connection if its input reaches EOF? I have a (non-standard) TCP service which reads all its input (i.e. until the client sends ...
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0answers
20 views

Changing the Retransmisson Timeout (RTO) estimation in Fedora

Retransmission Timeout(RTO) in a TCP plays a vital role in the internet. There are many algorithms proposed for calculating the Retransmission timeout. RFC 6298 is used for the estimation of RTO. I ...
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0answers
62 views

nginx server never resolves

I have set up an nginx server which is a proxy for port 80 to http://127.0.0.1:3000, but the request never gets through. It just infinitely loads. I have tried sudo /sbin/iptables -I INPUT -p tcp -m ...
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0answers
43 views

Cannot access server outside of server`

I have a node server listening on port 80. If I send a request to it like this: request('http://127.0.0.1:80',function(err,res,data) {console.log(data)}) It works. It returns what I would expect. ...
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4answers
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Killing tcp connection in linux

I have some dead connection in one application which is in hanged state if client machine is dead. ->192.168.1.214:49029 (ESTABLISHED) Is there a way to terminate these option from linux ...
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0answers
39 views

WARNING: at net/ipv4/tcp.c:1654 tcp_recvmsg

Our Linux based device (3.7.2) experiencing following issue when we try to do FTP or SCP over WiFi Connection. Same will work on Ethernet Connection or on TFTP. Here is the dmesg log for this issue: ...
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1answer
111 views

pfsense tcp connection between openvpn and lan is broken

I am trying to connect openvpn clients into an internal lan, so they can access a http server. pfSense as well as my http server are running on a virtual machine of my home proxmox node. Both are ...
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4answers
1k views

Writing a TCP server in bash [duplicate]

So, I recently found out about how you can send TCP packets through the /dev/tcp/hostname/port file, but my main problem here is how I receive them. I want to make a bash script that can host a TCP ...
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2answers
179 views

How to know if port 25 is blocked?

I am running Debian Jessie 8.1. The VPS provider says that port 25 is open. However, when I installed Rainloop and am not able to use it with the System users. Under the RainLoop admin panel I went ...
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1answer
552 views

Can nmap display only hosts with specific ports open?

Can nmap list all hosts on the local network that have both SSH and HTTP open? To do so, I can run something like: nmap 192.168.1.1-254 -p22,80 --open However, this lists hosts that have ANY of ...