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.
909
questions
2
votes
1
answer
1k
views
What would prevent a TCP server port (once closed), from being re-opened right away?
I have a server program that uses TCP.
Sometimes, I need to restart the program for updates, or any other reasons, but when I do, the program closes the server port, and then once it restarts, it ...
- 75
0
votes
1
answer
410
views
QEMU: SYN/ACK ignored on host in host-only networking with tap interface
I'm trying to set up host-only networking between my Linux host (running Fedora 33) and a QEMU instance (a fork for Xilinx devices), more specifically between a bridge interface (host) and a tap ...
- 11
0
votes
1
answer
571
views
socat resetting USB port on open
I'm having an issue with socat, and it is probably just in my environment.
I need to have a USB serial port redirected to a TCP port. I use the following and it works perfectly:
socat TCP-LISTEN:4444,...
- 1
0
votes
1
answer
3k
views
Configure openvpn for ExpressVPN TCP ports
I want to use the openvpn client on my Ubuntu 20.10 to connect to ExpressVPN's VPN.
Unfortunately I have to use the TCP ports, as the UDP ports are blocked.
ExpressVPN's website only allows to ...
- 389
0
votes
1
answer
2k
views
SSH file transfers slow with lots of TCP retransmissions
Good evening,
I use SFTP (File Transfer over SSH) from a computer (Windows 10) to a Synology NAS. Both devices are behind NAT on different locations. Around 3 weeks ago, whenever I initiated a ...
- 31
0
votes
1
answer
1k
views
Why do I get a "TCP Retransmission" right after having sent a packet?
I have a program (in Python) that publishes information to a bus (MQTT, implemented by mosquitto). This is a "fire and forget" kind of message, that is there is no long term subscription, ...
- 3,133
0
votes
0
answers
738
views
After opening port 443 in windows firewall as inbound rule, I cannot see it when I run 'netstat -an'
As an inbound rule on Windows 10 firewall, I added port 443 as TCP connection allowing all types of connections. However, I cannot see it when I run 'netstat -an'. How can I get it so that I see my ...
0
votes
0
answers
500
views
TCP port number reused
I am using STM32 TCP Echo server client Cube IDE example. I have server and client device. I can connect first time successfully but when I reset the client, I get after 70 line in wireshark ...
- 105
0
votes
0
answers
140
views
Chunked HTTP response does not come through completely
Consider the following setup
+-------+ +--------+ +----------+
| | | | | |
| +----------->+ +---------->+ ...
0
votes
1
answer
301
views
Modbus TCP Master-Slave
I have a problem with modbus master and slave TCP communication,
On windows computer:
When Master and Slave connect each other they communicate successfuly on 50905->502 ports, when I disconnect to ...
- 105
0
votes
1
answer
549
views
How does the server get the correct MSS value in the TCP triple handshake
When the client establishes TCP connection with the server, it will report its MSS value during the third handshake. According to my understanding, the MSS value should be obtained by subtraction 40 ...
- 1
0
votes
1
answer
208
views
is "Empty reply from server" a deliberate reply, or a default one from the TCP/IP stack?
I have a device whose port 80 is open and I was wondering what is behind:
~ # curl -v http://192.168.10.253 root@srv
* ...
- 3,133
1
vote
1
answer
455
views
Why HAProxy tcp-request content do-resolve is not working
i am using a combination of HAProxy (docker image v2.3.2) and Hashicorp Consul (v1.9.1) to access my VMs behind haproxy using SSH (i followed https://www.haproxy.com/fr/blog/route-ssh-connections-with-...
- 111
0
votes
1
answer
342
views
Relation TCP acks and MQTT acks
Is it somehow possible for a MQTT client to receive an MQTT PUBACK message without having received the TCP ack?
for example: The client publishes a message with QoS 1. The broker receives this message ...
- 103
0
votes
0
answers
878
views
java.exe opens up hundreds of ports on 127.0.0.1 on a windows 10 computer and listens to itself
After I ran netstat -ab with admin right on my win10 computer, which is not running anything "java" related on the desktop nor there is "java.exe" in taskmanager's "detailed ...
- 103
1
vote
0
answers
38
views
Disable instant closing of TCP connections when interface or route becomes unavailable in Windows
Whenever there is a brief glitch with my ethernet connection, Windows 10 instantly closes all of my TCP connections going over that interface.
Is there a way to change it so that the connections are ...
- 111
0
votes
1
answer
2k
views
Exporting TCP Connection Latency in Resource Monitor
In Resource Monitor in Windows 10 I am looking to monitor and log out the latency of for a particular TCP connection.
In Performance Monitor there is the option to create a data collector set but I ...
- 143
0
votes
1
answer
171
views
Log a TCP stream so it can be opened in Wireshark
I have an application that opens a TCP socket and sends and receives some data binary data. I would like the application to be able to log the sent and recieved data into a format that can be opened ...
- 101
1
vote
0
answers
44
views
understand ss -to4 output for a jdbc connection
My application connects to a database over JDBC, and performs a lot of sequential inserts. There is only 1 JDBC connection opened by the application. As the performance is not as expected, I started ...
- 11
0
votes
0
answers
49
views
How to set different TTLHOP for TCP ports
We want to set sensitive TCP/UDP Ports at low TTL/HOP Leaving other ttl/hop at 128 default
data center = 3
Priv net = 8
Internet = 128 default
Ssh 22 = 8 (internal hop max)
Rdp 3389 = 8
Http 80 = 128 (...
0
votes
1
answer
1k
views
Troubleshooting transport layer connectivity issues with pfSense
I am building a virtual network of vhosts that is NATed out to the internet through pfSense. For some reason, vhosts cannot establish connections to the outside world, although lower-layer operations ...
- 156
0
votes
1
answer
593
views
Sniff tcp connection and forward to TCP connection on other adapter
I have a system with two network adapters. One of the network adapters is connected to a port mirror, so it sees all the traffic in the network. I'd like to sniff that connection for a certain TCP ...
0
votes
1
answer
1k
views
Traceroute/tracert fails to receive hops return information
I noticed that with some routers/gateways
when I issue a traceroute or a tracert in a 'inner' computer
the hops always fail with:
request timed out
can anybody clarify this?
what information goes ...
- 958
1
vote
1
answer
71
views
Assigning IP addresses manually
I have internet connection from a local ISP at home. I see other routers and their IP addresses on my network using wireshark, when I connect the ethernet cable from ISP directly to my laptop using ...
0
votes
1
answer
244
views
How can I stabilize my wireless internet connection if it keeps dropping?
My current internet connection is very unstable. I'm using a Windows laptop connected to a 4G smartphone's Wi-Fi hotspot. The 4G signal is often so weak that it disconnects my phone from the network ...
- 867
0
votes
1
answer
88
views
Attack on a Linux file server | What is the damage of this file contents?
TCP Networking
This file was uploaded using a loophole in a file uploading network program I was writing. The ability to access the server itself was too simple and the techniques I used resulted in ...
- 11
0
votes
1
answer
384
views
Is sending a file with multiple TCP streams a good idea?
Imagine I got a large file and I want to send it through a TCP connection. The typical way is to use a stream and send continues bytes through it. But the question is, is it possible to send this file ...
- 23
1
vote
1
answer
2k
views
How do I capture packets between a WiFi router and an internet modem?
In my home all devices were connected to my router. I want to capture all traffic so I have done below connection:
Modem --- (Ethernet to USB Adapter) --> Laptop (Windows 10) --- (Ethernet CABLE) -...
- 111
-3
votes
1
answer
80
views
Why does my IPTables changes not deny access from all IP addresses except CloudFlare’s ranges?
I am running apache on ubuntu 18.04. I used IPtables to deny access from all IP addressed except CloudFlare’s ranges and when I run iptables -L –line-number I get
1 ACCEPT tcp – 131.0.72.0/22 anywhere ...
1
vote
2
answers
1k
views
three way handshake in application protocols?
I was reading an article (https://www.inetdaemon.com/tutorials/internet/tcp/3-way_handshake.shtml) which says:
FTP, Telnet, HTTP, HTTPS, SMTP, POP3, IMAP, SSH and any other protocol that rides over ...
- 141
0
votes
1
answer
456
views
Samsung Smart TV UA43N5300ARLXL/UA43N5300ARXXL unable to connect to internet over UFW firewall
I have a home network with a Raspberry Pi at the center running Pihole and UFW. The Pihole is both the DHCP as well as DNS server.
Ever since I started using Pi Hole I've not had any issues until ...
- 21
1
vote
0
answers
2k
views
SSH fails to connect from one computer but works from other computers
Problem
I have an external VPS server running Ubuntu 18.04 with openssh-server 7.6p1. I can connect via ssh to this server from many different networks except from one particular client. This ...
- 111
1
vote
1
answer
54
views
PC suddenly cannot do layer 3 communications any more
A PC running Win7x64 always functioned properly until a power off yesterday. From then on, the IP layer of its 3 network interfaces (2 LAN, 1 WL) only partially function any more.
A backup was taken ...
- 11
0
votes
0
answers
3k
views
buffer deadlock prevented error from RTSP streaming over UDP
I have an issue to view RTSP streaming over UDP in the open VPN connection.
Our project is to integrate 360 degree IP camera in unity system. And we want to get the UDP streaming rather than TCP to ...
0
votes
1
answer
97
views
network connection works only once
I have setup a home server and did port forwarding for http/ssh/tcp etc on the router. It was working well until very recently. My problem is that now connections seem to work only once from outside ...
- 181
1
vote
2
answers
2k
views
Packet reaches OS but not the process
Sorry if my issue is a bit hard to summarize in the title. That is the best I could come up with.
TL;DR Version: How do I debug when packets reach OS, but not the destination process?
Explanation: I ...
- 123
0
votes
1
answer
4k
views
Client not sending ACK packet in response to SYN-ACK
I'm seeing a weird network behaviour with my TCP 3-way handshake in my home lab.
Setup is from my Windows 10 host on one network, through pfSense, and into an Ubuntu VM on a different one. Firewalls ...
- 309
1
vote
0
answers
538
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, ...
- 11
0
votes
0
answers
257
views
Utility to display received TCP data
I'm writing code that consumes a TCP protocol - no authentication you just connect and wait for data.
I'd like to display & save this data nicely formatted - e.g. hex - and before I waste time ...
- 5,256
0
votes
1
answer
919
views
When connecting via SSH, does the Diffie-Hellman key exchange take place over an unencrypted TCP session or does encryption occur before the exchange?
I'm a cybersecurity student and I'm eager to understand the basic processes of an SSH session. I wrote down the stages to the best of my ability, but need help understanding what happens right after ...
- 7
0
votes
1
answer
1k
views
TCP RST when connecting via telnet to the application - Windows
I have an application running on Windows.
The application listens on port 54000.
I can connect to the application from the local machine and it works fine:
telnet 127.0.0.1 54000
Now, I am trying to ...
- 141
4
votes
1
answer
5k
views
How can I know what is preventing my socket to bind to localhost:50060-50959
I am using this Python code to listen to a port on my Windows 10 system:
import socket
for port in (50059, 50060, 50959, 50960):
try:
print(socket.socket(socket.AF_INET, socket.SOCK_STREAM)....
- 1,658
6
votes
1
answer
12k
views
Capture only TCP SYN-ACK packets with tcpdump
I'm trying to capture only TCP SYN-ACK packets, i.e. with both SYN and ACK bits set with:
tcpdump -vvvni eth0 tcp[tcpflags] == tcp-syn and tcp[tcpflags] == tcp-ack
but it gives such error:
tcpdump: ...
- 234
-1
votes
1
answer
913
views
What is TCP over SSL [closed]
There is this application called "TCP over SSL Tunnel". In his office, he only has access to education sites through the internet. He is using this application and connects to an accessible site over ...
- 3
0
votes
1
answer
310
views
What address type do DNS queries use?
I was reading this thread and it was mentioned that DNS servers use anycast address. I have also heard that there is something called Unicast DNS as well.
So, my question is what type of addresses ...
- 13
4
votes
1
answer
5k
views
Do socket and buffer mean the same thing?
I think my question is fairly clear. I was reading this article to understand how sockets work, and it mentions the terms socket and buffer interchangeably :
Assuming the packet is in sequence, the ...
- 125
1
vote
0
answers
75
views
How do Flow Control and Congestion control work together?
I am trying to learn about Flow Control and Congestion Control in TCP.
So far I understand that flow control uses the sliding window method and the receiver advertises a receive window based on how ...
- 13
0
votes
1
answer
91
views
How is network congestion detected in TCP?
I am trying to learn about Congestion Control in TCP and in this video (at 1:56), he says if there is no ack received, it assumes network congestion and cuts back the cwnd, no where he mentions about ...
- 125
0
votes
1
answer
490
views
When is the TCP receive window advertised?
I am trying to learn about the TCP 3 way handshake and flow control. I was reading this and I understand that in the 3 way handshake the sender and receiver agree on the Sequence and Acknowledgement ...
- 125
1
vote
1
answer
920
views
Port forwarding stops working after a while
Second day in a row I am having a hard time setting up port forwarding on my mac. I was working on a micro service and wanted to utilize through web. I might have messed up some settings, because a ...
- 111