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.
14
votes
4answers
1k views
TCP dies on a Linux laptop
Once in several days I have the following problem. My laptop (Debian testing)
suddenly becomes unable to work with TCP connections to the internet.
The following things continue working fine:
UDP ...
13
votes
5answers
44k views
How to check whether firewall opened for a port but not listening on the port
We will be deploying a new application to a Server and the application will be listening on port 8443. We have asked Network team to open the firewall for the port 8443 on that server before deploying ...
2
votes
1answer
24 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
15 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
20 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 ...
10
votes
3answers
16k views
How do I reserve ports for my application?
How do I reserve a list of ports for my custom applications?
To be specific, the product I'm creating has a lot of processes and a lot of intercommunication between them.
The problem I'm having is ...
4
votes
1answer
732 views
How to investigate a random reset on TCP client port connected via loopback interface to a server
I have a test suite which initializes a server on the localhost and then runs thousands of stress tests which include starting and stopping clients connecting to this local server on same machine. I ...
4
votes
1answer
87 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?
2
votes
1answer
614 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 ...
2
votes
2answers
27 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
16 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 ...
28
votes
7answers
31k views
Linux: allowing an user to listen to a port below 1024
I need to allow an user (different from root) to run a server listening on port 80.
Is there any way to do this?
2
votes
0answers
56 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
76 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/$PID/net/tcp file for example and get ...
0
votes
0answers
28 views
Too many “ESTABLISHED” connection
I have a setup where my client talks to the server via CORBA connection.
Both client and server runs on different machines.
When I start my client a connection is "ESTABLISHED" with the server.
Once ...
6
votes
1answer
151 views
How were these Linux TCP default settings decided?
I spent quite some time tracking down a problem in production recently, where a database server disappearing would cause a hang of up to 2 hours (long wait for a poll() call in the libpq client ...
4
votes
3answers
75 views
Why do some TCP reset packets show up in my iptables log?
I started to add some basic iptables rules on my Debian Jessie server. My objective is to filter and log network traffic (for security and learning purposes). Disregarding ICMP packets, these are ...
0
votes
0answers
82 views
Optimizing kernel TCP stack / parameters for services running on one host and communicating over TCP
I have a dual server {} block setup for my webapp running on nginx. For learning purposes I want to play around with performance tuning:
Questions:
What happens to a request going from one server ...
3
votes
0answers
35 views
Using socat to Tunnel/Proxy TCP want to split send/receive into separate files
I'm using socat to dump plain TCP (e.g. HTTP) traffic:
socat -v tcp-listen:$PORT,reuseaddr,fork,keepalive tcp:$TARGET_HOST:$TARGET_PORT
At the moment all send and receive traffic is dumped into ...
3
votes
2answers
91 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 ...
3
votes
1answer
366 views
nc -l in background closes immediately (nc -l 1234 &)
When I put this
nc -l 12345 >nc_out
in a shell script, run it and then connect from other shell using telnet, it allows me to type some text and have it end up in nc_out.
But if I start nc in ...
2
votes
0answers
61 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 ...
5
votes
3answers
14k views
Killing tcp connection in linux
I have some dead connection in one application which is in hanged state if client machine is dead.
->192.168.1.214:49029 (ESTABLISHED)
Is there a way to terminate these option from linux ...
2
votes
3answers
247 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
89 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 ...
10
votes
4answers
13k views
Logging outgoing connections as they happen
Is there a way to log to file all the outgoing connections that a process creates? I am aware of netstat but that seems to be more of a snapshot of a point in time rather than something that runs and ...
1
vote
2answers
119 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
90 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 ...
0
votes
1answer
103 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
93 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
2answers
175 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 ...
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
71 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
1answer
152 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 ...
4
votes
3answers
711 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 ...
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 ...
16
votes
2answers
57k views
Orphaned connections in CLOSE_WAIT state
I've got a SLES machine that accumulates TCP connections in a CLOSE_WAIT state for what appears to be forever. These descriptors eventually suck up all available memory. At the moment, I've got 3037 ...
1
vote
0answers
74 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
57 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
40 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
...
10
votes
1answer
642 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 ...
2
votes
0answers
130 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 ...
17
votes
1answer
7k views
Is it better to set -j REJECT or -j DROP in iptables?
There's an example of iptables rules on archlinux wiki:
# Generated by iptables-save v1.4.18 on Sun Mar 17 14:21:12 2013
*filter
:INPUT DROP [0:0]
:FORWARD DROP [0:0]
:OUTPUT ACCEPT [0:0]
:TCP - ...
1
vote
1answer
63 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 ...
10
votes
2answers
15k views
Fast way to copy a large file on a LAN
I am having some trouble with NFS, and I'd like to try using just plain old TCP.
I have no idea where to begin, though.
Hardware-wise, I am using an ethernet crossover cable to network two netbooks.
...
0
votes
1answer
215 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. ...
2
votes
1answer
108 views
Capturing data from a Fluke 1620a via Bash /dev/tcp file descriptor
I am currently trying to develop a script that will connect to a Fluke DewK 1620a Themo-Hygrometer and pull the current temperature and humidity readings from the device. While these devices have a ...
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 ...
0
votes
0answers
52 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 ...
