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Questions tagged [tcp-ip]

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TCP/IP quits after 48 hours

I have a problem with a (remote) server running SCO UNIX. It's been working for years, but was recently moved, and I changed its IP address & gateway address. Since then it works perfectly until ...
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0answers
22 views

writing data out to already opened port

I have a setup in which one unix program (s51 from a microcontroller simulation package) is a server tied to a specific port. Let's call the port 111. I also have setup a client on the same computer ...
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1answer
81 views

using PPP without TCP/IP

I'm using a PPP to communicate with a device. So far what I have been doing is instantiating PPP on my machine (Fedora 29) and on the device (Yocto Linux). Then I open a TCP/UDP socket and communicate ...
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0answers
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tcpip mss, should we think about a more versatile approach?

Reading RFC 879 TCP provides an option that may be used at the time a connection is established (only) to indicate the maximum size TCP segment that can be accepted on that connection. This ...
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2answers
248 views

Send TCP packet to the same source [closed]

I want to design a system which reduce travel time of packet what is happening in reality is I send a SYN bit from client side, this bit travel through router then to server and server reply SYN+ACK ...
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2answers
98 views

Routing multiple Virtual IP (192.168.11.X) to connect with test server (192.168.10.246)

We are trying to setup a test bed for our server testing, to simulate multiple connection / msg handling, I am trying to connect to our test server from a virtual IP. on the client machine (Debian) ...
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2answers
5k views

How to map an IP address to localhost

So I have an IP Address 5x.2x.2xx.1xx I want to map to localhost. In my hosts file I have: cat /etc/hosts 127.0.1.1 test test 127.0.0.1 localhost # The following lines are desirable for IPv6 capable ...
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0answers
124 views

TCP Stack tuning,(TIME_WAIT) - python process ignores sysctl setting?

I'm playing around with tuning various tcp settings for high number of outgoing client connections. I've put following in my /etc/sysctl.conf on Ubuntu 16.04. net.ipv4.ip_local_port_range = 18000 ...
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1answer
782 views

UDP or TCP hole punching to connect two peers (each one behind a router)

I'm trying to connect directly (without 3rd party server) my computer to a friend's computer. We are both behind a ISP router, and would like (as a challenge!) to connect without modifying the router ...
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0answers
44 views

linux failed to assign local port

Our nginx reported a error below: 2017/10/19 10:47:40 [crit] 41689#0: *23414459 connect() to 127.0.0.1:1234 failed (99: Cannot assign requested address) while connecting to upstream, client: 10.0.0.1,...
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1answer
180 views

Unordered ACK answer

is there any body knows ; how a server answers to client what if they send first packet as non-syn or the server finish the connection and wait for a new connection instead of getting an ACK or push ...
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1answer
58 views

why doesn't port 80 show up via firewall-cmd command?

Doesn't port 80/http need to be explicitly opened like other ports (such as 443/https or 8080/server), or is it a special case? on my machine (CentOS Linux release 7.3.1611) firewall-cmd --list-...
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0answers
49 views

syncookies and tcp options

enabling syncookies is helping against some attacks but the official docs still say syncookies seriously violate TCP protocol, do not allow to use TCP extensions Today I discover that once upon ...
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0answers
114 views

Connect beaglebone black running Debian Image 2015-11-12 to PC through Ethernet.

I have the Beaglebone powered through 5V and the ethernet in a open port on my PC. I have added the lines to /etc/network/interfaces auto eth0 iface eth0 inet static address 192.168.1.80 ...
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0answers
38 views

IS there a means of identifying the application path for the process which attempts to access the internet on a linux distributution?

Is there a means (kernel mode API) under Linux (any distro) that can identify the application path of a process that makes a connect() call and is attempting to access the internet ? Vice versa in the ...
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0answers
100 views

Does Linux have a Windows Filtering Platform equivalent?

Does Linux use a similar or equivalent platform such as what Windows has in the case of WFP? Where you can map the application path or application name to the data packet among other details of which ...
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0answers
100 views

How to emulate LAN adresses locally?

I have this situation: a piece of software got hardcoded IP address (let assume it is being 196.10.10.100:20000) to which it binds a socket and sends TCP and UDP traffic to 196.10.10.9:20000 (...
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1answer
61 views

intercept traffic generated by pktgen

I'm generating traffic on a Linux host with pktgen. I thought I could intercept it with tc and apply certain actions, but apparently pktgen bypasses it and writes directly in driver. Is there a way to ...
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2answers
1k views

TCP keep-alive parameters not being honoured

I have a server running on my Linux box, also on which the following commands were run: $ cat /proc/sys/net/ipv4/tcp_keepalive_time 7200 $ cat /proc/sys/net/ipv4/tcp_keepalive_intvl 75 $ cat /proc/...
4
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1answer
792 views

How do I set a static IP address for a disconnected interface?

I am setting up an Arch/Manjaro-based machine that only occasionally will be connected to network. I.e. most of the time its Ethernet card is disconnected. I run into this curious problem - when I ...
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3answers
35k views

Simple shell script to send socket message

For testing purposes I need to create a shell script that connects with a remote IP>Port and sends a simple text TCPIP Socket message.
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0answers
498 views

change TCP_TIMEWAIT_LEN at runtime

Linux kernel defines a timeout to destroy TIME-WAIT state of a connection in include/net/tcp.h: #define TCP_TIMEWAIT_LEN (60*HZ) Is there a way to change this parameter at runtime, via sysctl or /...
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1answer
608 views

How authentication is done between two nodes in tcp/ip or udp client server socket

I have a client socket program and server socket program in C TCP/IP . I execute the server program first on a port say 5000 and then executes client program on the same port and then server respond ...
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1answer
1k views

ICMP - Destination unreachable (Port unreachable)

I have two Ethernet-wired connected devices. I gave to both of them address from same sub-network. As result I can see second device in arp-table of the first. $ arp -a ? (128.247.77.90) at 10:60:4b:...
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1answer
4k views

How do I configure Docker containers to have unique IP addresses that are not the default ones?

How do I configure Docker containers to have unique IP addresses that are not the default ones? The Docker containers will run Apache or some web service. These Docker containers will share one host ...
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0answers
935 views

Why my server cannot serve more than 400 concurrent connections

I have an Ubuntu 14.04 LTS, kernel 3.13 in a Intel Xeon + 8Gb box. It has apache 2.4.7 configured in mpm worker with up to 4000 workers. The max bandwidth allowed by the ISP is 100Mbps. If I test ...
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2answers
22k views

ICMP : Port unreachable error even if port is open

I am testing my Debian Server with some Nmap port Scanning. My Debian is a Virtual Machine running on a bridged connection. Classic port scanning using TCP SYN request works fine and detects port 80 ...
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0answers
94 views

TCP/IP routes when using multiple DHCP servers

I have connected a computer (running Debian Wheezy) to two different DHCP servers (routers) through a cable and through a wifi device. If I look at the routes with route, I get the following result ...
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3answers
338 views

Unable to figure out how to route a packet through a multi-homed nic

The environment is FreeBSD for the most part and looks like this: HOST_A <-> ROUTER <-> LOKI <-> HOST_B Minimally, I would like to be able to ping ROUTER from HOST_B. ROUTER is ...
0
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1answer
2k 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. ...
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1answer
518 views

ip_conntrack and FreeBSD

We can figure out number of connections in GNU\Linux with ip_conntrack module, And I can print current connections and maximum of connections with: root@debian:/home/mohsen/test/shell# sysctl net....
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1answer
34 views

How does tcp communicate back to the application? [closed]

Are there standard sytem calls to send data to TCP? And back? How does TCP tell the application to send more or less?
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1answer
2k 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 ...
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2answers
2k views

“tcpdump” to capture the last packets

I am monitoring a certain port, because my application uses that port, it seems that the connection drops at random times, I want to see what are the last packets passing through before the connection ...
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3answers
169 views

Is it bad to select remember me option in the browsers of a compromised machine?

I was reading an article on how to sniff network packets. (of course for knowledge purposes only). I came across these particular lines. For instance, say I was sniffing traffic on the network, ...
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1answer
13k views

Comunicate with remote Serial over TCP/IP as /dev/ttyX device

I've one serial device on 192.168.x.x:yyyy (where "x" and "y" are real number) and it works correctly. But I want to communicate with this as /dev/ttyX device. I've tested socat command but not ...
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1answer
3k views

Does an in-kernel firewall sit between the network access layer and Internet layer?

This question is a follow-up to my previous question. Logic for me to says that an in-kernel firewall sits between the network access layer and the Internet layer, because it needs to have access to ...
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3answers
1k views

Disabling PHY auto-negotiation during Linux boot process on Xilinx

I'm trying to install Linux on an FPGA board. The linux flavour is petalinux for Xilinx FPGA chips. The current Xilinx SoC has a Cortex A9 processor and a programmable hardware logic i.e FPGA. I ...
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1answer
7k views

What does net.ipv4.tcp_app_win do?

I can't figure out why do these variables coexist in Linux. The information from man tcp says (Ubuntu 12.04): For tcp_adv_win_scale: tcp_adv_win_scale (integer; default: 2; since Linux 2.4) ...
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1answer
996 views

How do I safely perform the below changes to network parameters on Solaris 10?

I need to change and test some TCP/IP network parameters on a Oracle Solaris 10 as a possible workaround for a bug in 'Oracle Hyperion EPM 11.2.1.0' in the development environment. I am not a Solaris/...