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.

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Tomcat is continues running, but stops responding

We are using aws (4 Core + 16GB RAM) running Ubuntu 16.04.4 LTS (Gnu/Linux) as host 1) Web Server to host our java web application 2) WebSocket server (Provided in Tomcat) 3) TCP server (built ...
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Bad adderss (EFAULT) with TCP send

I have a very basic tcp code which sends some data on an active connection using write(). Sometimes on a very big data transfer, I see tcp_send return with EFAULT and if I retry the transmission ...
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Limit outgoing tcp syn packets

I want to rate limit outgoing TCP SYN packets to prevent syn floods from local virtual private server customers. Since the virtual private servers use the macvtap driver I cannot use iptables. I have ...
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EC2 SSH connection refused after changing elastic IP and reboot

I've browsed several dozen copies of this question but none of them seem to fix my situation. I have already checked: permissions on pem key (it worked before) checked correct new ip in ssh config ...
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socat - multiple connection attempts fail to pass through serial

I'm using socat to route serial input over a network to allow me to control an Arduino device over a virtual COM port setup. My command to start socat is: socat /dev/serial0,b500000,raw,echo=0 TCP-...
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How to use IP_TRANSPARENT to avoid too-many-TIME_WAIT

I've heard that we can avoid the issue of "too many TIME_WAIT" with the help of IP_TRANSPARENT in TCP/IP connection. In this way, it seems that a RST is used to disconnect, instead of FIN and ACK. ...
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Is this number of active connections normal in a reverse ssh tunnel?

I've some problems with TCP connections on my VPS. Sometimes the maximum number of connections allowed on the server is reached and ssh conections are refused. I've a few devices connected to the ...
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Ssh connection refused due to reach max socket TCP limit

I've a VPS and a lot of device connected to VPS thorugth a reverse ssh tunnel. Lately the vps rejects the connections because it has reached its maximum limit of tcp connections and I read how to ...
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omnios: how to disable tcp_timestamps?

On linux with tcp timestamps disable, the hping3 command confirm is working sudo hping3 linuxserver -S --tcp-timestamp -c 1 HPING linuxserver (bridge0 192.168.0.2): S set, 40 headers + 0 data bytes -...
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Why can't the UDP coming from nc command without -v be captured by tcpdump

Saying that I have two machines in my LAN, A and B. I execute tcpdump -i eth0 port 1234 at A to capture the packet coming from the port 1234. Then I execute nc -u -v -z -w2 IP_OF_A 1234 at B to scan ...
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NFS v3 TCP one specific socket high number of drops and larger rcvbuf setting than others

I have a lot of NFS v3 (TCP) activity on my CentOS 7.7 system, and I have noticed some latency which I am investigating currently. During my investigation, I'd noticed that out of the several TCP ...
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NFS client source port on reconnect

I am using NFS client to connect to NFS cluster. I have noticed that the default behaviour when server is unavailable is to retry the TCP connections from the same source TCP port, which I have ...
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tcp turning for high query [closed]

Server Details: Centos 6.9 1GIG Uplink IPV6 We query an external server via a TCP port and if they have a collection of delays then we fire higher query rate. I am trying to tweak the TCP stack ...
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44 views

logging TCP flags

I use nftables for my rules. my question: How can I log the tcp flags ? this is my rule : nft add rule filter input tcp dport 22 ct state new tcp flags \& \(fin\|syn\) ==\( fin \| syn\) ...
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TCP clients connecting outside of defined port range

A TCP server runs on an Ubuntu 18.04 box. Here's the local port range configuration on this box: blah@blah:~# sysctl net.ipv4.ip_local_port_range net.ipv4.ip_local_port_range = 32768 60999 The ...
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75 views

How to resume a file transfer using netcat or socat or curl?

I have to transfer a 400Gb database consisting of a single file over the Internet from a server where I have full control to an other computer at the opposite border of the ocean (but which uses a ...
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22 views

Sending TCP packets to specific back-end worker through Linux gateway

I'm looking for a way to implement a gateway that will route TCP packets from clients (1-4 client hosts), to specific back-end worker (docker container), according to some specific identifier (task_id)...
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How to gracefully stop process that runs a tcp server on specific port?

I have a systemd service unit that starts a tcp server on a specific port on the host machine. but on restart the port cotinue to run and if I restart the service I get an error address already in ...
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What does the '=' mean in iptraf?

What does the '=' mean in iptraf(Version 3.0.0)?
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Allow the contents of a server port to be accessible to public

I have a live, automatically updating plot(using Bokeh) in python being displayed in a remote Linux server(set up by my university for me) at its port 127.0.0.1:5006. Usually, I have to connect to the ...
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Why telnet is considered to be a protocol? Isn't it just a simple TCP send/echo program?

This is more like a conceptual question. I need some clarifications. Today I was learning some socket programming stuff and wrote a simple chat server and chat client based on Beej's Guide to Network ...
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63 views

Test iptables from localhost

I have a Linux system with two interfaces lo and eth0, I have some iptables rules which will block some tcp ports. It's possible to teste my own firewall rules by implementing a probing service to ...
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117 views

Adding qdisc under the mq top-level qdisc

This LWN article suggests that one may add/replace the network scheduler for a queue "under" the mq "dummy scheduler." These two point to that end: The mq scheduler does two things: - present ...
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/dev/tcp/host/port, /dev/udp/host/port what kernel module is this?

I noticed this in the bash(1) man page. Is there an operating system or certain kernel module that provides this interface? Tried it on my Debian installation and these devices do not exist. ...
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118 views

mysql database won't allow tcp connections on localhost at the default port

Trying to connect to a database with a c++ program. I am using the mysqlcppconnector with the connection strings tcp://localhost:3306 and tcp://127.0.0.1:3306. The program works on my local machine, ...
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How to send new lines from file to a tcp port?

Wait for file changes and send new lines to a TCP port server. I've tried nc 127.0.0.1 1234 -c "tail -F /var/log/changes.log" & But get broken pipe
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Why does the TCP handling mechanism in the OS wait for an ACK from client before sending [duplicate]

Im observing the below behavor in a TCP connection between a server application and a client which run on two different red hat machines. Example 1 Client acks everything until now (ACK with WND = ...
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Why is a packet is not sent until ACK is received when window size is sufficient

The considered application (server) has a number of clients connected. It processes each message from the client and sends two output messages. The output messages are generated sequencially and ...
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31 views

netcat is timing out before timeout has reached

I am trying to test a port on a remote machine. The connection is over satellite, so latency is quite high. I am testing with NC with the -w option to set the timeout. Ex: nc -w 300 address port ...
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Tcp connection packets ignoring network delays, ping shows delays [closed]

I've introduced a 2000ms latency to all network packets using openwrt netem module. # This is run on the terminal of the OpenWRT router tc qdisc add dev wlan1 root netem delay 2000ms I can clearly ...
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Linux TCP, how to debug unexpected delays writing a stream?

Problem: my music server code, using a simple TCP connection on a blocking socket, needs to stream bytes out to a client (happens to be a Logitech squeezebox). It's not complicated - read 64k from a ...
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Detailed output of ss command

I would want to know the meaning of some items in the ss command output. Eg: # sudo ss -iepn '( dport = :3443 )' Netid State Recv-Q Send-Q Local Address:Port ...
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tuning TCP setting for higher data throughput CentOS 7

I rent a CentOS 7 VPS wich I use as media server. My connection to this server is 21Mbits/s(Up&Down similar) with one open stream. When I add to iperf3 the parameter -P 10 for ten parallel streams ...
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Uhttpd requests stucks my device

I have a Web Server running on a devices under uhttpd. I have N devices ( N could be 25 ) that send request to the main devices. Everything works correctly when the main devices is running, but during ...
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142 views

Is it possible to force ending of (close wait) connections?

when we run lsof on port 6060 as the following # lsof -i TCP:6060 | more COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME app_lot 3495 root 12u IPv6 9238779 1t0 TCP *:krb0934 (...
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Is the non-open port response [RST, ACK] normal? [duplicate]

When the server port is not open then receive the [SYN] header TCP, is the response of [RST, ACK] normal?
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32 views

Many Send-Q have packets TCP connections, is this abnormality? what caused this?

The 125.193.242.25 is a CDN node, and when I analyze the TCP connect, there shows below information: [root@hkk10 ~]# netstat -na Active Internet connections (servers and established) Proto Recv-Q ...
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Reusing TCP port of a killed process

I have a TCP server process on Linux. It sometimes gets killed by SIGKILL, after which its parent restarts it. I cannot change the way the child is killed. Sometimes (about once per 100 times) the ...
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36 views

Collect information on TCP retransmissions

I'm collection monitoring information in my PC. Right now, I want to collect the total number of TCP retransmissions, from the moment I turn on the interface (similar to collect information from files ...
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Networking, netstat -na, RWind Size Dying?

So I have a windows 7 server setup (TCP) for multicasting outputting some data on the IP: 192.168.1.50:15000. It's just ASCII text that is being updated every second, but it could vary between .5 ...
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producer connect to consumer with unix domain sockets

I have this: producer-client | consumer-server the consumer starts a tcp server listening on a unix domain socket (something like that), and the client (the producer) will connect to it. However, ...
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Linux virtual servers: how does connection tracking work with direct server return?

How does Linux virtual server (LVS, set up with ipvsadm) do connection tracking when the real server does Direct Server Return? The LVS machine only sees the SYN and SYN-ACK packets from the client ...
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unsupported DLT type: BSD loopback (0x0)

Simply trying to replay a PCAP-NG file $ file 2019-05-23-after-16-05.pcap pcap-ng capture file - version 1.0 using $ sudo tcpreplay -i lo 2019-05-23-after-16-05.pcap $ sudo tcpreplay -i ...
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Send connections from minecraft port 25565 to another server [duplicate]

I have a domain name domain1.com and I want if someone want to connect (via minecraft) on port 25565 that the connection is transfered to another server. So: connect to domain1.com:25565 ==> ...
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72 views

What does the reordering field of ss --info mean?

ss --info returns information about tcp connections. It produces a line simliar to the following (some fields removed for formatting) tcp ESTAB 0 0 192.168.1.177:60236 54.70.141.88:...
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109 views

How to keep netcat open using it as a TCP tunnel?

Say I am doing something like this: (bsd variant of nc) nc -k -l 8080 <fifo | nc 10.90.34.18 80 >fifo This works great, I can use the server this is run on as a proxy to reach 10.90.34.18. ...
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160 views

How to talk to a tap device on Linux from another computer

I am running Linux on VMware Fusion on my Mac. On Linux, I am using a TCP echo server based on TAP devices (it's called PicoTCP, link here: https://github.com/tass-belgium/picotcp). I run the echo ...
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105 views

How to initiate hping3 with sack (selective ack) option in TCP options

I have a scenario on Linux machine, where I wanted to see if tcp-mss set with lowest value possible (say 48 bytes) along with the sack (selective ack option) of TCP header. On my Ubuntu client, cat /...
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1answer
148 views

TCP checksum wrong for zero length egress packets (captured with iptables)

I send TCP data between hosts (the topology is created using network namespaces and veth-pairs). For a host, I save its ingress and egress packets to pcap-file using NFLOG and tcpdump with the ...
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2answers
143 views

pacman (arch linux package manager) outgoing comunication port

I have to block all outgoing connections on ports that are not used, but i can not find the port used by pacman to synchronize and update/install packages. On the internet, i found that pacman uses ...