Questions tagged [tcp-ip]

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Does exist a current machine's “registry” of assigned ports?

I use several proxy instances to crawl the web with some bots (politely of course). To do it I launch a script with the following command polipo socksParentProxy="127.0.0.1:${NbSocksPort}" ...
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How to access Advanced Options for Ubuntu in rEFInd?

I'm trying to install Multipath TCP on my Ubuntu 20.04 and it requires me to do some steps in the Advanced Options. Steps in Advanced Options rEFInd shows only shows me Ubuntu, Windows, ?.
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140 views

Ubuntu 18.04.5 error messages: TCP: request_sock_TCP: Possible SYN flooding

I run Ubuntu 18.04.5. It has worked perfectly for quite a while on a computer integrated with an AVR via HDMI and with my LAN primarily via wired ethernet. I replaced an aging receiver with a later ...
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30 views

TLS handshake decryption

I have an offline Pcap file with a lot of data from many different protocols. I would like to decrypt the Transmission Control Protocol data from the 3-way handshake. Transmission Control Protocol ...
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382 views

TCP ports 139 and 445 keep reopening after reboot

I ran nmap a few days ago on my Ubuntu desktop and got the following: l@L-Ubuntu:~$ nmap 192.168.0.50 Starting Nmap 7.80 ( https://nmap.org ) at 2020-09-25 07:12 -03 Nmap scan report for L-Ubuntu (192....
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52 views

Is there any way to resctict telnet to communicate with C++ TCP server [closed]

I have a TCP server developed in C++. Currently, it's allowing all connections in the XML bytes length protocol. Due to some security reasons, is there any way to restrict access from the client using ...
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156 views

What do I need to tweak to avoid TCP duplicate/out of order ACKs during file upload from some computers?

I'm seeing an issue with a specific combination of circumstances that causes TCP duplicate ACKs to be sent. This happens with a service hosted on Ubuntu Server 20.04. I have a web service that, among ...
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447 views

Ubuntu 20.04 - Lag spikes when connected to wireless networks

Recently (I guess since upgrading to Ubuntu 20.04) I notice periodic heavy lag spikes when I'm connected to a wireless network. These manifest themselves e.g. as HTTP requests that suddenly start ...
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1answer
43 views

Is it possible for a bug in the source code ports of the network(TCP/IP)?

That may not be a logical question. But I would like to understand this. Any service that provides services on the Internet Has a set of specifications and ports based on standards and tasks. To ...
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402 views

I am able to ping to my machine IP but getting site unreachable on browser

My mobile and Desktop both are connected to a router. When I am making a python server from Desktop on 0.0.0.0 on port 6500 I am able to ping it from my mobile (using Termux) but not able to access ...
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429 views

Delphi Indy TCP Socket Server Sometimes Freeze and What is the limit

I made TCP Socket Server application. Embedded GSM module devices are connected with TCP/IP protocol on GSM Line and send about 140 bytes of data in per 1 minute. I parse this 140 bytes of data and ...
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47 views

Could not connect when port forwarding?

I have a server that I'd like to be accessible from outside my home network. On my router, I am forwarding port 8978 from the server, and my server is running a php script and listening to port 8978. ...
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1k views

TCP send performance issue on 18.04

I am playing around with Ubuntu 18.04 and I'm noticing TCP performance regression that prevents me from upgrading my current running servers since they are very latency-sensitive. For my particular ...
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1answer
197 views

Server stops accepting connections after ~120,000 active on 18.04.3

I'm running a type of perf test where I have a simple TCP server with 4 IP addresses that is listening on a port and getting connections from several other computers on the local network. Everything ...
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1answer
235 views

How to disable rhythmbox port 3689?

I installed rhythmbox on Ubuntu 18.04 LTS, since VLC several times hanged/crashed the GUI during video play. But by suprise rhythmbox is listening on the public IP (not localhost) on port 3689, ...
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1answer
9k views

Redirect an external IP to localhost?

Is it possible to redirect all calls to an external IP on internet, to localhost (without use of hosts)? I have an old application and I don't have the source code and this application try to connect ...
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2answers
978 views

tcp_probe could not insert 'tcp_probe'

I'm Trying to Work with tcp_Probe, but I became this error: ERROR: could not insert 'tcp_probe': Function not implemented my kernel version is : 4.15.0-55-generic Ubuntu I have seen, that many ...
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35 views

TCP session is not timing out even when link is shut

Distributor ID: Ubuntu Description: Ubuntu 14.04 Release: 14.04 Codename: trusty Sequence of steps: Using nc -l 9999 started listening on Ubuntu VM. Ran nc client is on another Linux VM to ...
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46 views

How to make an outgtoing TCP connection through specified netwrok interface?

Is there a way to implement in C program a next feature: it's need to making outgoing TCP connections through specified network interface? as example: eth0 - 172.16.0.1 eth1 - 192.168.1.1 In some ...
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704 views

Ubuntu 18.04.1 LTS keeps killing my Ethernet connection when it cannot find an Internet connection

I have a device (a nuclear radiation detector, specifically) that streams binary data over a TCP/IP connection. To stream the data, I simply connect it to my laptop via Ethernet and set the wired ...
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1answer
87 views

Ubuntu Networking to Allow Connecting to Host Machine

I have a Unity project and a ROSBridge host. When I run the Unity project from a windows machine, it can connect to the ROSBridge as hosted by two different Ubuntu machines. Putting the Unity project ...
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198 views

Forwarding Traffic From One Port to Another and Vice Versa

The goal: Have process A send messages to process B and vice versa via TCP (I'm using ROSBridge). The problem: Only one process can use a port at a time The solution (?): Have process A use port ...
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367 views

Sending a custom TCP packet

I am building a program that extracts transport layer data from packets, I want to test it but I couldn't find a way to specify TCP flags using netcat. Is there a tool that does this for Linux, or is ...
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735 views

How to permanently close a port?

I tried first adding a firewall rule sudo ufw deny 22 $ sudo ufw status To Action From -- ------ ---- 22 DENY ...
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2k views

Cannot run PostgreSQL on port 5432

When I try to start PostgreSQL on port 5432, it fails saying it can't connect to the tcp address. However, after changing the config to port 5433, it starts just fine. waiting for server to start.......
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267 views

keep receiving SYN_SENT on my server

can anyone explain this ? one is from a chinese ip the other a ip by Digital Ocean. I been track them and they keep sending this SYN_SENT on all non used ports The server is a public dns so they are ...
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766 views

Ubuntu 18.04 LTS: Slow down on localhost after recent update

I have been developing a network enabled application and been testing it on 127.0.0.1 (localhost). The application is completely memory bound, i.e. it never touches the hard disk. The procedure of ...
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135 views

How to configure port for external access?

I need to access software from another machine in PORT 3000, but I can not do it for the IP of the machine, only by localhost. erick@erickmordecai:~$ ifconfig enp3s0: flags=4163<UP,BROADCAST,...
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403 views

Unable to access Docker NGINX on 18.04 LTS

I'm running Ubuntu 18.04 LTS. > docker-version Docker version 18.06.0-ce, build 0ffa825 I run: > docker run --name my-nginx-1 -P -d nginx > docker port my-nginx-1 80/tcp -> 0.0.0.0:...
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335 views

Bluetooth PAN: permanent piconet

I need to create a PAN with BlueZ 5, to form a piconet (the most basic Bluetooth network) and send TCP/IP traffic on it. I must not share internet access, it should be a simple private PAN between the ...
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1k views

iperf3 shows that udp with set bandwidth is still x2 slower than tcp

I opened iperf3 server on host 192.168.1.105: iperf3 -sV Then client on TCP on same host: iperf3 -c 192.168.1.105 -4b 10G -P 2 -n 10G -w 1M Results are: - - - - - - - - - - - - - - - - - - - - - -...
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604 views

Changing TCP ACK delay

TCP ACK is described here: https://en.wikipedia.org/wiki/TCP_delayed_acknowledgment I know very little about this - I just learned about it via this ticket that I filed with Node.js: https://github....
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462 views

How to manually allow external access to ports 14141 TCP and UDP in linux 16.04?

I require external access to ports 14141 TCP and UDP. I need to manually allow access to these ports. I am an absolute beginner. Detailed steps would be highly appreciated. Thanks!
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2answers
87 views

Why ip addresses on local network [closed]

My question is more "philosophical" than practical. Since all hosts on a Ethernet local network NIC have a MAC address that identifies them uniquely, why does the dhcp service assigns them an ip ...
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1k views

tcp_probe function not implemented

Good day! I was trying to load the module "tcp_probe" when I got the following error "modprobe: ERROR: could not insert 'tcp_probe': Function not implemented" for reference, my kernel is 4.15.7 and ...
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721 views

nslookup working fine but ruby http call throwing error - getaddrinfo: Try again (SocketError)

nslookup and dig are resolving the address but ruby program throwing error. here is the stack trace 10: from /usr/local/bundle/gems/rest-client-2.0.2/lib/restclient.rb:67:in `get' 9: from /usr/...
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331 views

ethernet not working - xubuntu

Here is the result of ifconfig eth1 Link encap:Ethernet HWaddr 08:2e:5f:86:46:c5 inet6 addr: fe80::a2e:5fff:fe86:46c5/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:...
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1k views

Connect two PCs via LAN

One PC is running Windows 7, and another one is running GNU/Linux 16.04. My goal is to transfer 75GB big data from one to the other.I have ethernet cable and I have already tried creating LAN(TCP/IP ...
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321 views

Wrap tcp listener script so that it uses a sock file instead

I have a program when run, starts listing on on port 12345 $ ./cool_script.pl My linux administrator says it's against the policy to open ports. He says I'm allowed to use ~/cool_script.sock (unix ...
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2k views

how to connect multiple clients on server

nc -l -vv -p 7795 This is the command for listen the port But i can connect only one client by using(nc localhost 7795) to the port,tell me how to connect multiple client to the port 7795
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5k views

Ubuntu 17.10 VPN

Enabling VPN connection from the Network manager automatically add's IPv6 address to DHCP Wired connection even if it's disabled on the settings. This causes the VPN to leak on all DNS address queries ...
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1answer
1k views

How to Reduce Buffer Bloat on an Ubuntu Based Router

I had an old Dell Optiplex 790 (added dual Intel PCI-E gigabit NIC) sitting around that I decided to make into a router using Ubuntu 16.04 and the guide found here https://arstechnica.com/gadgets/2016/...
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4k views

Postgresql refusing TCP/IP connection after ubuntu restart

This one has me baffled. I rebooted my ubuntu server and now I try to connect with pgadmin and I get the following: could not connect to server: Connection timed out (0x0000274C/10060) Is the server ...
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38 views

kernel 4.9.20-040920-generic with a TCP ACK number incorrect issue

hi all we use tcpdump to capture packets from a TCP receiver site. As the pic shows, TCP ACK number is incorrect: The kernel we are using is 4.9.20-040920-generic, is this a bug of this kernel ...
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1k views

What user permission is required to listen to port 8080

I'm trying to run Cuberite under its own username, cuberite. However, when I sudo -u cuberite ./Cuberite I'm unable to connect to it with my web browser: $ sudo lsof -i :8080 COMMAND PID USER ...
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1answer
728 views

Why can't I ping the IPv6 loopback in my Vagrant Box?

I watched a video tutorial about the loopback address. I learned that 127.0.0.1 is the IPv4 loopback address, localhost also points to IPv4 loopback address, and ::1 is the IPv6 loopback address. ...
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1answer
669 views

How to configure iptables to work with tcpcrypt?

Background OS: Ubuntu 16.04 x64 running on VirtualBox I am a developer with minimal Ubuntu/Linux knowledge and have been assigned to a project where the goal is to utilize tcpcrypt when ...
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1answer
638 views

Use nmap scan specific ports to see which IP addresses are running any of those

I have a question to write a script using nmap to look at TCP ports across the entire network to identify which IP addresses are running any of those services. Sorry my english is not good.
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1answer
5k views

sysctl: cannot stat /proc.sys/net/ipv4/tcp_frto_response

I'm trying to tune some tcp parameters to enhance the performance of the wireless network I have. One of those system parameters are tcp_frto and tcp_frto_response. The first value I was able to read ...
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2answers
399 views

TCP communication with robotic arm -Destination Host Unreachable-

I'm trying to communicate with a robotic arm via TCP/IP communcation. It works well on windows but when i try it on linux matlab i cannot connect to arm. Matlab tries to connect again and again ...