The Transport Control Protocol (TCP) is a low-level part of the protocol stack used by the Internet. It sits directly above the IP layer and is responsible for making sure that dropped packets are resent.
2
votes
1answer
23 views
Alternative of ArpRetryCount in CentOS
ArpRetryCount Implemented by Microsoft and the following is its descritption :
Determines how many times TCP sends an Address Request Packet for its
own address when the service is installed. ...
1
vote
1answer
13 views
Iptables dropping HTTP 302 packages contain suspicious domain string
The HTTP 302 packages I want to block have:
Header
HTTP/1.1 302 Found
Location: ...
1
vote
0answers
16 views
How to download a video from rtmp protocol from behind proxy using rtmpdump
I am trying to download video from rtmp://flash.dce.harvard.edu/bounce/mp4:2015/01/14328/L01/14328-20140902-L01-4-h264-av1248-16x9-852x480.mp4. My college internet runs behing proxy, Is there a way I ...
2
votes
2answers
26 views
Using remote XServer
I recall seeing a tutorial on setting up Xorg to be a vnc replacement without installing anything, but I cannot find it. I was hoping someone here could help out. Scenario:
Machine A
no monitor
...
0
votes
0answers
14 views
How do I increase my network perform on Centos 7
I am doing some research and I find that I have to configure the sysctl.conf file if I want to increase the network performance.
So, I want to configure the default maximum Linux TCP buffer sizes ...
2
votes
0answers
50 views
Why do I have Established TCP connections with no owner PID?
Both ss --processes and netstat --program (with sudo) list some ESTABLISHED TCP connections to local port 6514 with non-zero Recv-Q values and no owner process (netstat output shows - where ...
1
vote
1answer
75 views
Read “/proc” to know if a process has opened a port
I need to know if a process with a given PID as opened a port without using external commands.
I must then use the /proc filesystem. I can read the /proc/$PID/net/tcp file for example and get ...
0
votes
0answers
27 views
Too many “ESTABLISHED” connection
I have a setup where my client talks to the server via CORBA connection.
Both client and server runs on different machines.
When I start my client a connection is "ESTABLISHED" with the server.
Once ...
4
votes
3answers
73 views
Why do some TCP reset packets show up in my iptables log?
I started to add some basic iptables rules on my Debian Jessie server. My objective is to filter and log network traffic (for security and learning purposes). Disregarding ICMP packets, these are ...
0
votes
0answers
82 views
Optimizing kernel TCP stack / parameters for services running on one host and communicating over TCP
I have a dual server {} block setup for my webapp running on nginx. For learning purposes I want to play around with performance tuning:
Questions:
What happens to a request going from one server ...
6
votes
1answer
148 views
How were these Linux TCP default settings decided?
I spent quite some time tracking down a problem in production recently, where a database server disappearing would cause a hang of up to 2 hours (long wait for a poll() call in the libpq client ...
3
votes
0answers
31 views
Using socat to Tunnel/Proxy TCP want to split send/receive into separate files
I'm using socat to dump plain TCP (e.g. HTTP) traffic:
socat -v tcp-listen:$PORT,reuseaddr,fork,keepalive tcp:$TARGET_HOST:$TARGET_PORT
At the moment all send and receive traffic is dumped into ...
3
votes
2answers
84 views
Distinguish TCP server from client within netstat output
I have a socket connection between a client process and a server process, both running on my machine. There are two entries shown for the connection as,
sudo netstat -ntp | grep 56442
tcp 1 ...
2
votes
0answers
59 views
Difference between MTU for a route and MTU for an interface
There is a server I connect to over the WAN and somewhere over the route there is packet loss unless I set the interface MTU to 600:
ifconfig eth0 mtu 600
Doing this causes problems with ...
2
votes
3answers
230 views
How to create a TCP listener?
Introduction: I have created a bash function that is able to check whether a port is available and increments it by 1 if false until a certain maximum port number. E.g., if port 500 is unavailable ...
0
votes
1answer
85 views
Effect of limiting tcp connections through iptables to limit ssh sessions
I have limited no. of tcp connections through iptables to limit total number of ssh connections. Now when i am adding a rule with maximum limit of tcp connections lesser than currently opened ssh ...
1
vote
2answers
110 views
lsof to identify incomming TCP connection
I which to know if my server establish a connection to a remote server or if the remote server tries to reach my server, I try to read the output of lsof and obtain this:
lsof -i TCP:25
USER FD ...
0
votes
0answers
82 views
Transparently Relay TCP Socket to Serial Port (and vice versa)?
I would like to create a psuedo serial device (such as /dev/ttyXXX0) that I can use to make transparent serial connections to an arduino that's on my wifi (via an esp8266 serial bridge). I would like ...
2
votes
1answer
569 views
Changing the TCP RTO value in Linux
I want to alter the TCP RTO (retransmission timeout) value for a connection, and some reading I have done suggests that I could do this, but does not reveal where and how to change it.
I have looked ...
0
votes
1answer
96 views
Meaning of 'netstat -anto' output
I did netstat -anto and got following result:
Proto Recv-Q Send-Q Local Address Foreign Address State Timer
tcp 0 0 127.0.0.1:1169 ...
2
votes
2answers
92 views
Linux kernel parameter “net.ipv4.tcp_workaround_signed_windows”
I am seeing some intermittent network issues when sending large amounts of data over a network and it has been suggested to me that setting this option to a 1 may possibly resolve the issue.
...
1
vote
1answer
47 views
What ports will an ssh daemon use outbound?
I am making a bastion ssh server. When I use the following rules in its ip tables, I am able to connect to the server just fine:
Inbound Rules
Allow traffic on port 22 from my client's IP
Block all ...
0
votes
0answers
68 views
Netstat command lists only 256 connections when I do SYN flood on my server
I have been trying to do SYN flood on one of my servers from an other machine.
And I am sure that I causing a DOS on it, but it actually shows only few connection.
That is when I type netstat -a | ...
2
votes
2answers
69 views
Binding two incoming TCP connections
I have a client to connect multiple devices. For not paying monthly static IP fee per device. We plan to change the architecture. In this new architecture devices connect to a server. Instead of ...
1
vote
0answers
73 views
How to enable Tcp\Ip remote connections in Centos 7.0
I am running Centos 7.0 using VMPlayer . I have set a private network shared with the host (Windows 7) .
On my Centos Server i have opened a tcp listener on port 10102 .
I could not connect to this ...
2
votes
1answer
54 views
How to enable SYN Cookies on Debian 7.5?
How do I enable SYN Cookies on Debian 7.5?
nano /etc/sysctl.conf
#net.ipv4.tcp_syncookies = 1 remove here the #
sysctl -p
service network restart
Is that the correct way? Or what must I look ...
1
vote
1answer
39 views
Unexpected netstat output in DNAT conditions
So, here I have a basic setup with SOCKS5 proxy listening on, oh, say 8123
I redirect TCP to the proxy via iptables
From iptables perspective everything looks peachy,
iptables -t nat -v -L shows
...
2
votes
0answers
124 views
What does an inode for a socket contain?
I read somewhere that the inode for a TCP socket would contain the buffer space. Is that true, and if so, does it mean that the inode contains a memory address for the buffer space used by the ...
1
vote
1answer
59 views
check tcp packets reception below tcpdump level
I am having an issue with my smartphone device and packets monitoring: I am trying to find a reason why I cannot establish a VPN connection via PPTP protocol.
I have the following successful ...
0
votes
1answer
59 views
Linux drop packets if received from another equipment
Problem description :
When I establish a VPN connexion between a VPN client and my home server, if the connexion are both across my firewall (pfSense) or are established directly, the connexion is ...
4
votes
1answer
81 views
TCP Westwood implementation available?
Is there a way to install TCP Westwood congestion control algorithm module for FreeBSD? If not, maybe there's a source code available that could be compiled into a loadable Kernel module?
0
votes
1answer
211 views
How can I edit /proc/net/tcp?
I need to edit 1 line in /proc/net/tcp while the file is also used by the linux kernel for updating other lines of it by the kernel.
Background: Each line in /proc/net/tcp represents a TCP socket. ...
0
votes
1answer
37 views
What happens to TCP when a write fails to enqueue with the device tx ring?
Lets say the device tx ring is full and you do a normal C non blocking write(fd, buff) to enqueue data in the TCP SND buffer.
What happens when this fails? In UDP - the packet would be dropped but ...
1
vote
2answers
172 views
Different Congestion Control algorithms in FreeBSD
Is there a way I can run a different (than the default) TCP congestion control algorithm in FreeBSD? I am trying to modify an existing TCP congestion control algorithm with some ideas published in ...
2
votes
1answer
149 views
socat duplicate stdin to each connected client
ncat (from the nmap folk) has a neat default action of duplicating any input to all connected clients. E.g.:
Start a server on terminal 1:
% mkfifo messages
% exec 8<>messages # hold the fifo ...
1
vote
2answers
264 views
tcpdump captures network-wide UDP traffic, but not TCP
When observing traffic with sudo tcpdump udp, it behaves like it should: I can see all traffic which is happening in the network, even when the machine which I am using is not involved.
However, when ...
2
votes
1answer
76 views
Close the neccessary Ports [duplicate]
I am using Linux Mint and I am newbie. Someone is trying to access my computer via my MAC Address and open port. I have some questions:
I know that there are different type of port like TCP and UDP. ...
0
votes
0answers
48 views
How much of Linux's recent TCP bufferbloat remediation also applies to SCTP?
I am looking at rebuilding an existing communications sub-system within a shared-nothing cluster. The current message protocol is built on UDP but layers on reliable, in-order delivery and ...
0
votes
0answers
130 views
Linux, dev/tcp validation and kill the process with timeout
I have this part of code, I need to validate if the connection was ok or not, AND, if the process is running more than 3 seconds, it will be killed. But, I dont know how to keep the value of the ...
4
votes
3answers
662 views
Tool to generate TCP traffic
I want to generate a TCP traffic starting from the port 0 to the port 65535. 1 tcp packet for each port with 1ms between 2 packets. The generator should not care if there is a TCP ACK or not.
Are ...
10
votes
1answer
620 views
D-Bus authentication and authorization
I'm trying to set up remote access to D-Bus, and I don't understand how authentication and authorization are (not) working.
I have a D-Bus server listening on an abstract socket.
$ echo ...
0
votes
0answers
277 views
Opening a TCP port in Linux
I am trying to establish a TCP socket between my linux server and my client running on my laptop. The TCP server code I am running is,
from socket import *
HOST = ''
PORT = 1999
...
1
vote
1answer
98 views
Test for open TCP port in bash script
I want to delay the script execution until a certain server process is ready, which it is once it accepts incoming TCP connections.
How do I test if a local TCP port is open (I get a SYN/ACK answer)? ...
1
vote
1answer
276 views
How to artificially open many tcp connection on a host (testing)?
I'm trying to build a test setup which test my server's performance under high load. In order to do that I want to open thousands of tcp connection. The problem is that I only have two hosts, one is ...
0
votes
0answers
60 views
why do I have so many open socket handlers and netstat DGRAM entries?
I run on a RPi (Raspbian 3.12.35+ #730 PREEMPT Fri Dec 19 18:31:24 GMT 2014 armv6l GNU/Linux) a daemon in Python 2.7.8 which queries various APIs via requests and provides itself an API for another ...
1
vote
1answer
86 views
Transparent proxying of TCP connections on port (mostly, without root access)
I have the Client machine living somewhere on the Internet, and it needs to access a custom port of Target machine (or, initially any port on any reachable machine, but, eventually, particular port, ...
3
votes
1answer
61 views
log PID of each connection attempt
Finding the PID of an established connection is trivial using netstat or lsof. However, I have a process which is creating a connection ever 60 seconds to our database and locking it up by maxing out ...
2
votes
1answer
227 views
Linux: monitor my own internet usage page by page
I have a monthly broadband subscription which rolls over on the 23rd of each month. I had arrived near the end of my usage so I was carefully checking that I didn't go over my limit - they crucify you ...
1
vote
3answers
716 views
Simple TCP server listening on a port but not returning SYN-ACK
I am looking for a command-line TCP server (preferably a one-liner), that will listen on a specified port and when received SYN, it will not respond with SYN-ACK as usual TCP servers do.
The purpose ...
0
votes
0answers
111 views
cannot change tcp-segmentation-offload
I have been doing tests with tcp-segmentation-offload on and off, but now I cannot seem to change the parameter anymore, it is stuck on "off"
(I can change generic-segmentation-offload)
...
