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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How passively monitor for tcp packet loss? (Linux)

How can I passively monitor the packet loss on TCP connections to/from my machine? Basically, I'd like a tool that sits in the background and watches TCP ack/nak/re-transmits to generate a report on ...
0 votes
0 answers
28 views

TCP & Wireshark: Retransmission not working?

I traced a TCP connection in wireshark and try to understand how ACK'ing should work correctly. As you can see in the picture at some point there's a paket missing from IPx.61. Wireshark tags this ...
3 votes
2 answers
38k views

Cannot ping through one of the network interfaces

Setup ubuntu linux VM ( virtual-box) is configured with two interfaces, eth0 and eth1. eth0 is on a bridged network and directly connected to external network. eth1 is on "nat network", which is ...
1 vote
0 answers
52 views

TCP & Wireshark - Server not re-transmitting segments?

I am new to TCP-in-depth-analysis which I need for a current problem. Connections: Client = Host PC, Ubuntu 22.04.4 LTS (IP: ...60) Switch (TL-SG1016D by tp-link, Gbit) Server = Proprietary embedded ...
0 votes
0 answers
33 views

Looking to monitor activity regarding connection attempts to closed ports on my system, what log file in should i look in? Ubuntu

I'm looking to monitor activity regarding connection attempts to closed ports on my system, as part of a server side portknocking implemetation. However, I am confused about what log file in ...
1 vote
1 answer
4k views

iperf test in reverse direction gives different result

I used iperf to measure the max throughput for TCP connection between two ubuntu machines. Both the machines were directly connected be means of a 1Gbps cable. When I performed iperf tests i obtained ...
0 votes
1 answer
26 views

RateLimit is doing weird maths and wrong numbers on kernel

I'm trying to apply a set of rate limit within iptables, and it's doing some weird maths that i'm not able to see on the kernel why this is happen. I tried to execute same code on my local machine, ...
0 votes
0 answers
142 views

IP over LoRa: TCP timeout

I am trying to tunnel IP packets via LoRa. For this I use two devices running Meshtastic. Using ICMP I was able to determine that there is a packet loss of about 30% of the packets and a latency of ...
0 votes
0 answers
100 views

NGINX Reverse Proxy Server sending RST to upstream and FIN to downstream after 5 Minutes of inactivity

My current nginx setup always kill the TCP connection after 5 minutes of inactivity, i.e no transaction. I have this setup which requires TLS1.2 connection connecting from my internal network [client ...
0 votes
0 answers
56 views

AWS ALB: Are Sticky Sessions possible with TCP?

I need to load-balance my clients. Some of these clients use TCP/TLS, the rest HTTP/HTTPS. The target services of the load balancer can be in either EC2 instances or ECS containers. Also, the clients ...
1 vote
2 answers
236 views

TCP port forwarding/tunneling by file sharing

I have a Linux server and a windows client. A folder is shared between these machines with read and write access for both of them. I want to access a production database from my development machine, ...
0 votes
0 answers
97 views

TCP_NODELAY for All current sockets in linux

i want lowest latency network with tcp_nodelay., in windows OS we can easily enable TCP_NODELAY through registry of windows. i searched on the red hat website and another website but up to now, my ...
0 votes
0 answers
632 views

OpenVPN TCP connection to firewall failing: unknown error

I am encountering an error when attempting to connect to my office using OpenVPN. The error message: Tue Jul 18 12:34:52 2023 WARNING: Compression for receiving enabled. Compression has been used in ...
0 votes
1 answer
38 views

What happens if a TCP implementation retransmits different data? [closed]

No sensible TCP implementation would do this, but does anyone know what happens in practice if a TCP endpoint retransmits different data for particular sequence numbers? I couldn't find anything in ...
12 votes
3 answers
50k views

How to kill a TCP connection using tcpkill utility

I'm trying to kill an ESTABLISHED TCP connection using tcpkill. The connection is an open HTTPS connection. It appears on netstat as: tcp 0 0 X.X.X.X:55601 X.X.X.X:https ...
31 votes
2 answers
7k views

Under what circumstances is TCP-over-TCP performing significantly worse than TCP alone (2014)?

Many admins keep perpetuating - on ServerFault and elsewhere - how bad of an idea TCP-over-TCP is, e.g. in VPNs. That even the slightest packet loss will make one suffer from at least severe ...
-1 votes
1 answer
61 views

How does real server, direct return server (DRS), reply to client if a load balancer (LB) uses port address translation (PAT)?

Direct Return Server overview: The DRS allows real servers to directly reply to a client without going through load balancer (LB). The LB ip (VIP) is configured as a loopback (localhost) ip for the ...
0 votes
1 answer
62 views

How to route TCP traffic through a fixed IP in Azure during local development?

Hello ServerFault Community, I'm working through a challenge related to accessing a third-party OPC UA server and am considering a solution using Azure's cloud infrastructure. Background Our team ...
0 votes
1 answer
36 views

Can iptables state miss some packets?

I tried to setup the iptable rules for MTA. As this MTA is meant only for receiving the emails I allowed INPUT packets from any to destination port 25 with state either new or established, and allowed ...
2 votes
1 answer
4k views

Nginx TCP stream routing based on source IP

I have configured nginx as a reverse proxy for a TCP (non-http) stream. I'd like to apply different routing for a particular source IP address - can this be done, and how? I'm aware of recomendations ...
1 vote
3 answers
4k views

Limit Number of TCP connections in Linux Server, to avoid attack

I want to limit the number of TCP connections in Linux server, I have used the following command. iptables -A INPUT -p tcp --syn --dport 80 -m connlimit --connlimit-above 25 --connlimit-mask 32 -...
0 votes
0 answers
25 views

Data from NF Tables to IP Tables

I have input data like below for NF Tables: nft add rule filter input tcp flags != syn nft add rule filter input tcp flags &syn!= syn add rule filter output tcp flags & (syn | ack) == syn | ...
0 votes
0 answers
44 views

Parsing TCP flag Data for IP Tables

I have input file which has data like below chain:VARIABLE_IN ip_version:v4 proto:tcp sport:5401 dst_ip:18.159.158.206 dport:5432 decision:a tcpflags:&syn!=syn My code reads above data to form ...
0 votes
0 answers
64 views

How to set TCP flags "&syn!=syn" in iptables?

I have requirement where am getting parameters to set in iptables as below: Rate Limit = 1/sec Source port = 5432 Source IP = 203.0.113.0 Protocol = tcp TCP flags = &syn!=syn iptables -A PRIO_IN -...
1 vote
2 answers
890 views

nftables: Possible to block SYN packets with payload?

Is it possible to drop all TCP SYN packets with a payload using nftables? The man pages mention various length options, but none that I could get to work for TCP packets without syntax errors. I am ...
0 votes
2 answers
2k views

Server Dropping all Connections Randomly and Packet Loss

I just built a server using a Supermicro X8DAH+-F board and running Ubuntu 10.04 Server 64bit. This has the Intel 82576 dual port controller (one port is disabled). Since this is a server, remote ...
2 votes
2 answers
5k views

How to measure TCP connection time in Linux

I want to measure the overhead in creating a TCP connection. I know of many tools like hping and netperf, but they seem oriented at measuring latency. I want to know how long the 3-way handshake ...
18 votes
5 answers
73k views

How to check TCP timeout in linux / macos?

I have a network problem on my MacOS that i need to troubleshoot. I know that TCP socket has internal timeout that will close connection if remote party is not responding (but no graceful disconnect ...
0 votes
1 answer
167 views

Remote Desktop intermittent connection issues

this post is related to this:Remote desktop connection by host name vs IP address but there's more info to be presented so decided to post a new one. when connecting to remote desktop using the ...
0 votes
1 answer
5k views

Kubernetes (K8S): TCP clients waiting very long timeout on connection to a Service when there are no Pods serving its requests

My problem occured when using Redis on Kubernetes, but it seems that it is not a problem with Redis itself, but with network/infrastructure. My scenario: I have a Redis Service with single Redis Pod ...
0 votes
0 answers
107 views

TCP 3-Way Handshake Issue: Client not responding with ACK

I have a Java application running inside a virtual machine (VM) that uses S3-compatible storage as an object data store. Periodically, the VM is destroyed, re-deployed, and reconfigured. During the ...
0 votes
2 answers
4k views

How can I avoid the error TCP_MISS_ABORTED/000 when uploading files through squid?

While uploading big files, > 10MB, through a squid V5.6, I noticed that they failed and/or were retried. The error has been logged multiple times in the logs: 1671092710.452 423 ::1 ...
0 votes
0 answers
86 views

Windows service on Windows Server 2019 stops accepting IoT device connections on public IP address and domain name

We are investigating an issue on Windows Server 2019. It runs a Windows Service that accepts TCP/IP connections (TCP/IP service bound to IP address 0.0.0.0, so listening on all network adapters). ...
3 votes
2 answers
5k views

TCP connection RST after FIN, ACK

I have a situation that would like to clarify with the experts here. I am no network expert so maybe it's normal, but i rather ask. We are trying to diagnose a problem between two servers, both are ...
1 vote
3 answers
211 views

I need a packet-level explanation of how HTTP redirects to HTTPS

I am programming an embedded web server and trying to figure out how to redirect all incoming SYN packets on port 80 to redirect to port 443. Everything I've found online is in the context of Apache, ...
18 votes
2 answers
64k views

How can I search the info column in Wireshark?

Wireshark | Windows I want to search a packet capture of SMTP traffic for specific addresses/messages. Normally, I just sort the info column and browse but it would be nice if I could just run a ...
1 vote
1 answer
77 views

TCP connection not arriving at process depending on source interface

I have a strange case where a TCP connection seems to not arrive on the listening socket, depending on the source interface. The context: I'm trying to configure the Zabbix agent on a specific host (...
2 votes
0 answers
206 views

How to debug curl when netcat works?

The following cURL command hangs: $ curl -v http://1.1.1.1/* Trying 1.1.1.1:80... * Connected to 1.1.1.1 (1.1.1.1) port 80 > GET / HTTP/1.1 > Host: 1.1.1.1 > User-Agent: curl/8.3.0 > ...
0 votes
1 answer
733 views

First packet isn't SYN

A Windows Server 2016 in DMZ is calling a time stamp provider service on HTTPS outside the company. The DMZ server is not a high traffic one, making around 2000 calls to the external provider per day. ...
0 votes
0 answers
204 views

NGINX TCP reverse proxy resolves queries differently

The Setup I currently have a server and a mongodb database running in the cloud (Oracle Cloud Infrastructure). The Problem My connection to the database is bound by a select number of static IP's. ...
0 votes
1 answer
208 views

Linux TCP tuning to overcome choking uplink

A linux computer is on a network link which exhibits the following behaviour: good download speeds upload/uplink starts well but after a few seconds drops to close to nothing. The Send-Q and Recv-Q ...
53 votes
9 answers
122k views

Why would a server not send a SYN/ACK packet in response to a SYN packet

Lately, we've become aware of a TCP connection issue that is mostly limited to mac and Linux users who browse our websites. From the user perspective, it presents itself as a really long connection ...
0 votes
0 answers
25 views

Allow access to local mongodb database to a different network

Is it possible to do tcp port forwarding using windows settings without having to access router settings? I am trying to give access to my local mongodb database to someone on a different network to ...
0 votes
1 answer
103 views

How does NGINX Plus handle server failure when doing session persistence for TCP/UDP communication?

My understanding from the NGINX Plus documentation is that their Load Balancing will route around servers that are down or swamped and that Session Persistence attempts to maintain the same server for ...
0 votes
0 answers
83 views

Repeated TCP DUP ACK of the same initial packets

I'm using Wireshark to analyze one of the TCP conversations in my packet capture and I have this sequence where the entire conversation between these two ports is made out of TCP DUP ACK for the same ...
0 votes
0 answers
118 views

Pgpool-II connection pooling with Load balancing disabled still make request to stand by DB node. Causing client to disconnect

I have a problem with pgpool-II load balancer. Currently I have turned off pgpool-II load balancer but somehow it still made request to my standby node. How can this happen? This make my child go ...
0 votes
0 answers
41 views

TCP connection severing in Two arm load balanced environment using Kemp LoadMaster connecting to Centos servers

The configuration is one that I inherited but the connection from the LoadMaster to two appserver ends up occasionally getting severed. This will happen to each server independently, and only seems ...
0 votes
1 answer
312 views

Understanding TCP RST Network Capture

I only really need help understand the following image, but I will give the background for context. We have an app that is configured to use a proxy on port 8080 and requires Internet access. At ...
1 vote
1 answer
37 views

Web browser fails to connect to website after 100 refreshes on client

I'm using an HTTP meta-refresh to execute a script multiple times. After 100 refreshes, the browser stalls. According to devtools, the browser doesn't even complete an initial connection to the server....
0 votes
0 answers
141 views

Automatic TCP SYN - cookie activation

I am simulating a SYN flood attack on a Raspberry Pi 1 with KALI Linux (ARM) installed. A similar message as mentioned in this post was printed after performing the attack: How to avoid syn cookies. ...

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