Questions tagged [tcp]

TCP stands for Transmission Control Protocol and is one of the core protocols of the Internet Protocol Suite. TCP complements the Internet Protocol (IP), and therefore the entire suite is commonly referred to as TCP/IP.

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What's the expected behavior in TCP when hosts don't specify the MSS during handshake?

Let's suppose there are two hosts A and B and they are going to communicate over TCP. I am curious about the behavior of TCP related to MSS. Wikipedia says default value of MSS is 536. But, RFC-793 ...
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Decoding TCP packets as RTP in Wireshark

I'm troubleshooting a WebRTC video calling problem in my app and i'm using Wireshark. One end of my video call is a web app running in my browser window and the other end is a Unity based app on an ...
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How to disable TCP packets with overlapping data in Windows Server?

Consider this short Wireshark packet capture on Windows Server 2016: Frame-1 TCP Window Size of client (192.168.201.5) is 1504 bytes. Frame-5 TCP Server responded back with a packet (length 1083). ...
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On a TCP connection, can the recipient control the TCP window size that the sender uses?

The TCP window size is the amount of data that the sender will send before waiting for a TCP ack. Does the receiver have a way to control this (e.g., as part of the TCP handshake), or is it only the ...
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Drawbacks of having pruned and collapsed packets

I am a newbie in networking field, I come across a note that we should not have pruned packets and collapsed packets, if we have, we should have to optimize the system. But the note (neither the ...
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GCP Network Load Blancing with internal IP Backend-Services

I try to configure an external TCP LB and 3 backend instances which have not any external IPs. I'd like to use only the LB external IP and reach the instances. After terminating the configuration ...
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425 Security: Bad IP connecting when trying to connect to ftp server behind load balancer

I have an ec2 instance with vsftp installed. The daemon is listening on port 21: $ sudo netstat -tulpn tcp 0 0 0.0.0.0:21 0.0.0.0:* LISTEN 1730/vsftpd I ...
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How to set TCP Fast Open cookie timeout?

TCP Fast Open: the server should periodically change the encryption key used to generate the TFO cookies, so as to prevent attackers harvesting many cookies over time to use in a coordinated attack ...
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Transparent TCP load balancing with NGINX/HAproxy

I have been trying for some days and still have no luck with getting transparent TCP load balancer to work using HAproxy/NGINX. The problem is: everything works correctly, until i try to enable ...
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How do common MPTCP schedulers behave by default?

Multipath TCP (MPTCP, RFC 6824) is a protocol that layers a "virtual" TCP connection over several "physical" TCP connections such that ordering and other TCP guarantees are preserved but seamless path ...
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Increase TCP server listen backlog size on Windows

I'm developing TCP server in Go which should be able to accept up to 500 simultaneous client connections. I'm using net.Listen("tcp4", listenerAddress) to create my TCP listener. I had a problem on ...
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Interpreting Envoy Proxy logs - has my data been sent?

I am trying to configure Envoy to act as a TCP proxy, where downstream connections are made to Envoy using TCP encrypted by TLS. Upstream connections are unencrypted TCP. The connections are long-...
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How to block the client confirmation of server's response?

Suppose I make a request to a server and when I receive the response, the server sets some flag to true. But I don't want the server to set that flag. Is there a way to manipulate the TCP ...
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What's the size of the SYN / ACK queue and how to change this parameter? (and other SYN flood mitigation techniques)

My provider informed me that a SYN flood attack has happened on a server (and they mitigated the Ddos). I understand that many SYN are sent by the attacker, SYN-ACK are sent by my server, but then ...
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Can't connect to EC2 via TCP

My Ubuntu 19.04 EC2 instance has security group with inbound and unbound rules set to all protocols, all ports and 0.0.0.0/0 IP range. I can connect to it with SSH on port 22 and with http on port 80,...
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TCP Duplicate Ack without Packet Loss

I have a sender on IP 192.168.2.250 running some embedded RTOS and a receiver running Linux 4.9.x on IP 192.168.2.1 The receiver is configured as a Wireless AccessPoint and the sender is directly ...
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How to automate nc ot ncat task

i need to create a script that connects via udp or tcp (both options are possible) to a server , then send the string "TEMP" , do something with response and then exits. This script should run on ...
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Client unable to get TCP communication with Server on a VM

Client is attempting to connect to a Server on a VM VM is using a bridged adapter Server CAN ping Client Client CAN ping server Wireshark shows a SYNC from Client to Server followed by 2 TCP ...
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Weird TCP/IP behavior on Linux server as well as enterprise Firewall on port 21

This is a tricky one. TL;DR: 1) Client establishes TCP handshake with the firewall on (closed/unavailable) port 21, even though firewall does not respond to client's SYN packet. 2) Client ...
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Block SYN,ACK response with iptables

I have a virtual environment and Iam making a SYN flood attack to a Ubuntu Server's port 53 using Kali 2020. I realized that a countermeasure for this attack is to limit or block the responses to the ...
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IIS/HTTPS - TCP Data ACK missing

I am having a problem with a server (Windows Server 2016) in production. I have a provider who sends me data via HTTPS and I have to respond to him via XML. I receive between 700 and 1000 calls / day ...
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Random “Connection resets by peer” with redis-benchmark

I've got several linux hosts in office network. When I run Redis server on one of them, redis clients receive random errors "Connection reset by peer". We've noticed these errors with our own ...
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Multiple TCP dup ACK with spurious retransmission

I have a cellular IoT-device connected to a MQTT broker with a keep alive of 15 sec. It happens once a day that the device gets disconnected from the server (server log shows: client stopped due to ...
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Diagnosing socket usage on GNU/Linux, matching data from different tools

I'm trying to understand a situation with a server I'm working on. My problem is summarized here: [root@server ~]# cat /proc/net/sockstat sockets: used 2338 TCP: inuse 15 orphan 0 tw 29488 alloc 438 ...
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What do the following mean: TCP:RA, TCP:FA ,TCP:PA, TCP:S, TCP:SEC

I'm specifically looking for a definition of what the following mean: TCP:RA, TCP:FA ,TCP:PA, TCP:S, TCP:SEC The context is that I'm looking at some pfSense logs which are showing rejected packets by ...
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Why can't I reliably send or recieve data over TCP after moving servers?

I am currently dealing with a networking problem on high latency (100-400ms) Internet links. I run a Minecraft network, and I recently moved it to a separate datacenter to get a server with a better ...
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Too long TCP handshake while doing NAT

I've installed Mikrotik hEX at location 'A', Mikrotik hAP AC^2 at location 'B', and connected each with OVPN L2. Both two routers have their NAT features turned on, and have their private network. hEX ...
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UDP comunication at the and of a TCP request

I'm learning about network protocols, in particular TCP and UDP. I've written a c++ client that get the HTTPS response of this page 216.58.198.35 (Google), then I've used Wireshark to analyze the ...
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How to Load Balance TCP connection based on custom packet data other than just port number (moved from Network Engineer stack)

Scenario I have 2 service instances listening for TCP connections behind a load balancer. When service 1 initiates TCP connection to the LB, one instance is randomly chosen to serve the request. ...
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SSH connection problems through OpenVPN tunnel (“TCP Previous segment lost”)

I have a VPN tunnel to an OpenVPN server. The VPN is a Sophos VPN which uses OpenVPN under the hood. I do not know the server configuration nor can I change the server config. My tunnel endpoint is ...
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How to redirect a packets from port 80 VM1 to port 8080 VM2?

I want to redirect all packets incoming to 192.168.1.2 port 80 to 192.168.1.1 port 8080, but what I am doing wrong here? On VM2 iptables -A PREROUTING -s 192.168.1.2 --dport 80 -j REDIRECT -d 192.168....
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Suricata - Log client connections and disconnections to the server

I have a server running multiple services, I use suricata to log tcp traffic. I don't need to see every request made by every client, I only need to log connections and disconnections of every client. ...
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How to route 0.0.0.0:22 to 192.168.122.179:22?

I want to route 0.0.0.0:22 to 192.168.122.179:22 which is a VM. This way I can access my VM through SSH by typinh the local IP of the host machine. However i get connection refused if I try to ssh ...
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Which load balancer is compatible with AMQP ( primarily Rabbit MQ ) protocol?

I am currently exploring Load Balancing which can load balance AMQP protocol requests. At the moment I am exploring whether envoy ( Which is one of the LB product ) There document says envoy can ...
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Firewall is causing a file download to fail halfway through

I have a strange issue which I belive is related to the Windows firewall settings. I have a client application that tries to GET a rather large XML file (around 13k lines). When the firewall is off, ...
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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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Dual Stack issues with Active Directory

I'm trying to set up a dual-stack environment with two Windows Server 2019 domain controllers. However, when I test the client as IPv6-only, the client fails to authenticate with the AD servers. The ...
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Can not ping from tun->wlo1 and wlo1->tun

I have created a tun interface from a C program. Now I want to send tcp packets from this interface. But I got an error like No route to host on this step. Steps to reproduce:- Created tun ...
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Any ideas on tuning single stream tcp performance?

I'm a newbie to TCP tuning and would really like some pointers to possible solutions. I have a Ubuntu 18.04 server with maximum bandwidth of 30Mbps. But simple downloading like scp or wget can only ...
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TCP VIP: client -> VIP connection behavior when VIP -> server connection is closed

Specifically talking about Citrix netscalers but I'm guessing the behavior is similar in other implementations The documentation mentions that in TCP VIP mode there is 1:1 mapping between the client -...
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AJAX POST fails - client sends RST response…why?

Problem We have a web application that is used by many thousands of users. However, since the latter part of Jan 2020, a tiny fraction of clients (but still a significant number) have reported a ...
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How to block specific port with iptables

I have a service running (docker registry) on my debian server at port 5000. I would like to restrict access to that to specific IP, so I've created a file with rules (1.2.3.4 is my trusted IP) *...
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How does Linux allocate bandwidth between processes?

If I don't set up any traffic shaping, how does Linux allocate (outgoing) bandwidth between processes? My specific situation is that I am running 30 identical processes on a cloud VM, each of which ...
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TCP Connection Visible Only On Linux

I'm dealing with an issue in the communication between two machines. Machine A is a Windows Server 2012 box, and machine B is a Centos 8 box. Machine A is a virtual machine running under VMWare, while ...
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Nginx fails on high load with Debian10 and not with Debian9

We had never any problems with nginx. We use 5 nginx server as loadbalancers in front of many spring boot application servers. We were running them for years on debian 9 with the default nginx ...
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High Traffic Server Configuration - Are We Doing It Wrong?

We have a REST API server with 25 million calls each day. Our stack consists of Haproxy + Gunicorn + Flask also we have a MongoDB database that's used by our Rest API. We monitor it with Netdata and ...
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Why don't I see the TCP handshake in the HTTP server?

When I create a simple http server (a socket listening to a port) I don't see the actual TCP handshake taking place. Why is that? Why is it hidden from me? For example if I start a server on port ...
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NIC GRO offload influence in TCP window size in Linux?

I am facing some, from my point of view, counter-intuitive results on some iperf3 tests between two 40Gbps interfaced servers (the rest of tcp stack config protocols are the same in the 2 servers). ...
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Limit IP access to TCP load balancer on GCP

After creating an external TCP load balancer, I want to limit internet access to it. There is proxy on/off setting to limit IP forwarding to HTTP/HTTPs load balancer. It is only for HTTP/HTTPs LB. ...
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Is there a way to limit Src Ports in IPtables masquerading

I have the following chain setup by kube-proxy in my iptables on all my Nodes. Chain KUBE-POSTROUTING (1 references) target prot opt source destination MASQUERADE all -- 0.0.0.0/...

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