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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Is there a way to hide a local IP address from an executable?

My Windows server has 2 IP addresses assigned to it. Is there a way to hide one of the IP addresses from an executable (windows service in this case)? The reason is that this application takes ...
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Python sockets: slow or no communication from centos8 linux, while same program from Windows10 works without issue

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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32 views

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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37 views

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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89 views

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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66 views

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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Cant create DAC logon to Sql Server

I am trying to create a DAC connection to Sql 2014 via TCP/IP, following various blog posts. Nothing seems to work, I keep getting "TCP Provider, error: 0 - No such host is known". Im ...
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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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199 views

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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166 views

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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27 views

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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When the results stored based on ipv6 flow label be used?

I have gathered some information on IPv6 flow label. It is used to identify a specific flow from one source to one destination and from the first new flow labelled packet received, the ipv6 header, ...
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249 views

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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82 views

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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1answer
48 views

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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51 views

Is it actually possible to send some data to remote destination over tcp/ip without any socket?

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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88 views

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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2k views

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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2k views

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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1answer
1k views

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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101 views

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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1answer
950 views

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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647 views

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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5k views

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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1answer
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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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658 views

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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35 views

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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2answers
75 views

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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1answer
2k views

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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45 views

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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1answer
495 views

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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1answer
130 views

why are there are so many svchost established connections to Isilon?

Our client has a Isilon (used only for smb) with few nodes attached to it. When I run TCPView I don't understand why svchost service established the connection and why there're so many of them: And ...
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22 views

Which parameters and setting affect network throughput when connecting two machines together without a switch?

I have a situation where I need best possible throughput (TCP/IP sockets & SMB3) between two Windows Server 2016 connect with a 1m patch cable. I have to use existing hardware. When you connect ...
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38 views

Weird behavior of VPS host

Hi I noticed strange behavior on my VPS host I launch nmap on my laptop and scan VPS host nmap screenshot Listed netstat on VPS server netstat screenshot Tried to connect to some port connection ...
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704 views

diffrence between csma/cd and tcp/ip

I finished my middle school IT & Networking education about 2 years ago. Now I recently got a job and started to refresh my knowledge. I've been searching the internet first of course but I still ...
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Windows 7 Client flooding network with DHCP requests. Not setting IP

I have a small network, with 15 workstations, SAMBA AD, and a bunch of Virtualized linux servers. All the workstations, and servers are on the same subnet. All workstations are running Windows 7 Pro ...
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1answer
1k views

TCP Initial Handshake Incomplete (ACK Missing)

I am irritated about the following scenario: I am running a MVC application on an IIS 10 Webserver. While calling the URI, it takes about 10 seconds until the application starts to get called (IDLE ...
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1answer
2k views

Why does TCP request packet contain ACK flag? [closed]

I am very new at low level of TCP and I am tryingtcpdump with simple socket server and client program. The server and client follow the two steps. Server and client make a connection. Client sends ...
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2answers
9k views

Linux: tracking the source of netstat -s “failed connection attempts”

I have several servers, where the failed connection attempts metric returned by netstat -s (from /proc/net/snmp) grows by roughly one per second, and I'd like to diagnose the source of these. By ...
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1answer
83 views

can only ssh unidirectional

I have two centos 7.2 server. One machine ip is 10.104.196.18, another machine is 10.240.197.21. I can successfully ssh from 10.104.196.18 to 10.240.197.21. But failed to ssh into 10.240.196.18 from ...

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