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Questions tagged [tcpip]

TCP and IP are two important protocols used in networking today. Due to their importance, the Internet Protocol Suite is also commonly known as "TCP/IP"

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Having Trouble Identifying TCP Congestion Control Provider option: Default

I am running a Windows 10 (Version 1909) OS and when I am entering the following command in CMD ... netsh interface tcp show global ...I am able to see add-on congestion control provider set to "...
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http timeout with docker bridge network, but port 80 is opened in firewall

I'm trying to install mailcow-dockerized in my server, but I'm having trouble with Docker network. I tried several ways, but I get lots of connection timeouts in containers. In order to breakdown the ...
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APIPA ARP requests are send all over the network

We have ~200 hosts running windows 10 and ~40 ip cameras all working with ip addresses from 10.100.0.0/16 almost all of them sending arp requests to 169.254.0.0/16. We have also virtual machines ...
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Transport layer port and firewall

When a communication is initiate the OS chooses randomly a port number greater than 1023. As long as it does not conflict with other ports in use on the system at that moment. I wonder how the ...
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Routing Issue: Cannot reach target server from local network

1. my setup: I've got an optical fibre ZTE router from my ISP for internet and telephone. My old analog phone is connected directly to the router using the dedicated phone port on my router. (For ...
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TCP handshake not completing intermittently to specific Cloudflare node

I have setup a webpage with Cloudflare that works nearly all of the time, except occasionally the TCP handshake fails with the SYN+ACK not making it to Cloudflare. On a packet capture from another ...
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Log TCP Client port on apache mod_proxy

Using an Apache 2.4 Reverse Proxy (with mod_proxy) that connects to a backend HTTP service we have the following(simplified) series of TCP connections: client ClientIP:random_port1 ---> <IP1:443 ...
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Route all internet traffic through vsock channel

I can run arbitrary code on both a Linux server instance and a Linux VM inside the server. Both can only communicate to each other through vsock channels. Only the server instance has internet access. ...
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HA Proxy TCP Content Rejection

I am looking for an option or a work around where I can accept or reject the TCP Content based on the the size of a file which is getting uploaded This settings is required on TCP IP layer only also ...
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How to load balance Socket Connections?

We have a large pool of devices that establishes socket connections with a server. Connections are TCP socket connections hitting a server IP: port pair from a destination IP port pair. In stand alone ...
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Is it redundant to add an extra checksum or CRC in TCP packets to make it possible for the receiver verify whether the data is same with the sent one?

As TCP contains a checksum and the TCP/IP stack will detect broken packets, is it redundant to add an extra checksum or CRC in TCP packets to make it possible for the receiver verify whether the data ...
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Is it useless to reply the received messages (on TCP) on application layer to tell the sender the messages have been successfully received?

Any data loss is detected and automatically corrected, which is why TCP is also called a reliable protocol. In other words, the transport layer is responsible for error-free, end-to-end delivery of ...
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Python sockets: TCP errors in linux, while same program works fine on Windows10

I'm trying to communicate with a commercial power supply device via TCP/IP using python sockets. I tried using both a virtual linux(centos8stream) and virtual windows10, both running at the same ...
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Determine if there's Network Traffic over a TCP/IP Connection using PowerShell in Windows?

I had a situation where an application was "hanging" in accessing the database. I was able to see that there was a connection by using Get-NetTcpConnection -RemotePort x This showed that ...
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How to forward client ip to App server via Haproxy TCP/IP loadbalancer?

I have configured HAproxy for TCP/IP loadbalancing but in app server I am not getting IP address of source instead of that I'm getting haproxy IP address as client ip address. I searched on google and ...
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TCP/IP: can i REMOTELY (via VPN) access mis-addressed device on remote LAN?

i sent a pre-configured box to client to drop onto their LAN. while i was sure i left it as DHCP, when i connect to the LAN through the VPN i'm not seeing it pull an address from the router and it ...
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Linux TCP stack does not send a RST after giving up on retransmissions

Several sources (one being my colleague and the other being TCP/IP Illustrated by Stevens) indicate that there should be a RST sent after the TCP retransmission attempts have been exhausted. I have ...
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Login attempts from 255 IP? (3.0.115.255)

today I see some login attempts from an unusual IP: 3.0.115.255 and I ask myself: how can this happen, that an IP ends with 255? I thought it's for broadcasting - can it be assigned to a single ...
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AutoSSH monitor echo port bind to specific IP

I'm using autossh for create ssh tunnel. Everything good excep paramiter -M of autossh. It cannot bind to specific IP to remote host. By default, it create 0.0.0.0:20000. I wanna bind to loopback IP: ...
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Proper behavior for a DNS Server when it is queried for a domain it doesn't control in the case of Split-Horizon DNS?

So one of our cloud providers offers a lower-latency, zero-rated "Internal Networking" option between VMs. The interfaces on the internal network are in the 10.x.x.x IP Space. When one of ...
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What would be the possible reason for server not send syn/ack pack for specific IP address?

we have a server that do not respond to a specific internet IP address. We have looked into firewalls but no obvious setting showing block the IP. From wireshark, we found that the server received syn ...
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DNS and OSI Layer Working

I would like to clarify a doubt that's haunting me after learning DNS. I'll briefly write it as a question. "A user was watching a video in youtube and suddenly the DNS server which was used by ...
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Linux connections to unused port timeout instead of being refused

I have a Centos 7 box I inherited where if I try to connect to an unused localhost port, the connection fails with a timeout instead of being immediately refused. Example below: $ nc 127.0.0.1 5800 ...
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Forwarded Packets are received by namespace's veth0 but not received by application

I use libtins (It uses Pcap) to capture link layer packets and forward to a network namespace where the actual application runs on. Client(Browser) -> Server -> Pcap -> Pcap Send -> br0 (...
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Sending files via FTP without IP addresses on PC's [closed]

Can two PC's communicate with each other - FTP, without using IP addresses(entirely skipping Network Layer)? I know, FTP is client-server architecture, but I wonder if LAN network and MAC addresses ...
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How does a PC determine which network adapter to use when given an IP/DNS to connect to? [closed]

I have so many network adapters on my PC. If I type for example "Ping 192.168.191.128", how does my PC now which network adapter to use? What if it's a DNS name like "mylocal.ddd.com&...
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Stop attacker without affecting others on same IP [closed]

How can I stop a client that's running a multirequest script on my server that reconnects and continues no matter what, without affecting the other people/clients that are connected to my server from ...
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How to enable ECN marking in IP header in Linux

Is the ECN marking in the IP header is performed by default in Ubuntu (4.15.x kernel) or should the kernel be recompiled with a special option? I configured a RED ingress queue at an Ubuntu machine, ...
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SSH connection not established, but standard TCP/IP connection works

I'm working on a custom yocto Linux for a Raspberry PI 3 and try to get the WIFI connection working with SSH. However when trying to connect from my PC (Ubuntu 19.10, SSH OpenSSH_8.0p1 Ubuntu-6build1, ...
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What do i need to take to connect an openvpn server to a local network?

I'm setting up an office vpn so people can work from home, by rdp'ing their office machines by connecting to a vpn server which is based on the office lan. It wont be as simple as creating a vpn ...
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Is it actually possible to send some data to remote destination over tcp/ip without any socket? [closed]

I am studying socket concept. As far as I learned socket is like electrical socket that is created in both end of communicating devices (or processes). Socket can keep itself alive forever to listen ...
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Ping a host in other network

I have a Virtual Machine One in inner network 192.168.1.0 with ip address 192.168.1.1 and Machine Two in inner network 192.168.2.0 with ip 192.168.2.2. Both have enp0s3 interface. How could I ping 192....
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TPC lost segment

I'm investigating an issue where the application (Java based) didn't receive the whole message which was split on two TCP segments. I have a trace that proves that both segments was sent to the server....
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How to add more than 2 DNS servers in a domain

I have 3 DNS servers in my environment that I'd like to show up on my end users machines for backup. 2 onsite and 1 in Azure. I have a site 2 site VPN connection between HQ and Azure. When I go to ...
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Windows Server 2012 R2 SYN Flood Attack?

I have a Windows Server 2012 R2 IIS web server, running on VMWare esxi 5.5, hosting multiple websites with different IP addresses. This server recently has been refusing connections randomly across ...
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How do I bind to UDP port 53 in GCE (Container-Optimized OS)?

Is there any way to free up UDP port 53 on my GCE instance so that I can bind to it? I'm running a container on GCE that needs to listen on UDP port 53, as it's listening for DNS connections. However,...
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DNS resolving timeout

I have a DNS in Linux Centos 7, and when integrating with Windows Server 2012 R2 it only solves in an inverse way, that is, with its IP address, when I try to resolve directly the server, it takes a ...
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Unable to connect to my winsock server using external IP

When I try to connect to my simple winsock server using my localhost/LAN IP, the connection is established with no problems. However, if I attempt to do so using my external IP, I keep getting ...
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6 votes
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Is there a TCP Maximum Segment Size (MSS) Minimum?

I have there a OpenVPN VPN network connection, where the MSS size 60 gets send out for some reason (don't know why yet). EDIT: Reason: OpenVPN mssfix was mistakenly set to 1 36 92.064383 10.102.0....
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2 votes
1 answer
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Tuning network interface for TCP over TCP in Linux

I'm porting a legacy embedded application to Linux. This application communicates with a remote server over a TCP connection using a proprietary protocol. In addition to the application specific ...
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Why TCP Out-Of-Order packet is seen after SYN?

I am trying to troubleshoot a performance issue between a client and a file server. When I look at the capture from the client, I see a weird behavior. I am trying to understand this weird behavior. ...
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10 votes
1 answer
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AWS flagged my subnet as invalid although it looks to be within the VPC CIDR block

My VPC CIDR block is 10.0.0.0/16 As I understand it, this should support 256 (effectively 254) subnets with 65534 hosts per subnet. When I tried to create one subnet 10.8.0.0/24 and associate it with ...
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How to debug IIS 8.5 TCP resets?

I have a Win 2012 R2 / IIS 8.5 server that has been running a handful of public-facing production websites for 2 years. Today, for about 6 hours, it started randomly dropping port 80 requests (but ...
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Connection timout between two IP troubleshooting

I have a client with a webserver and a VPS server with a webserver and a mailserver. These machines have to exchange data via REST API but I have a problem, they are not reachable each other over HTTP ...
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What is the difference between net.core.netdev_max_backlog and net.ipv4.tcp_max_syn_backlog

Several docs on the net describe these options as following: net.core.netdev_max_backlog: Maximum number of packets, queued on the INPUT side, when the interface receives packets faster than ...
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Why does LAN stops working if switch is connected to two upfeeds?is [closed]

If I connect my switch to two upstream feeds from my ISP, my internal LAN stops functioning (see illustration below). What is it in the TCP/IP protocol that is disrupted to cause the above? ...
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2 answers
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Is there URL filter like protocol in TCP/IP stack?

I find many type routers have their self-existent URL filter settings. Tenda: Nexxt: So, is there a URL filter protocol in TCP/IP stack? and if is, is there any software for controlling every ...
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How can iperf reporting packet loss in udp

Iperf is the well known tool to calculate throughput. When i tried udp throughput using iperf on my linuxpc, It reported that 10% of packet loss. In UDP protocol, data gram did not receice any ...
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Windows Server 2011 - System opening ominous TCP connections

Where I work we have a Windows Server 2011 Small Business edition, and recently our Symantec software started reporting "blocked intrusion attempts" from port 80. Our routers do not forward any port ...
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2 votes
1 answer
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Sysinternals Sysmon: How to log an unsuccessful TCP/IP connection attempt

I would like to use Sysmon to log an unsuccessful TCP/IP connection attempt. For example, with the following configuration: <NetworkConnect onmatch="include"> <DestinationPort condition="...
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