Questions tagged [tcp-ip]

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Can a NAT router run out of ports?

The highest TCP port number is 65535. If a router doing NAT uses an ephemeral port for each connection made to the internet on behalf of the hosts on the internal network, does this mean that it is ...
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-Y and read {src,dst} port and tshark

tshark get data from interface or pcap files. When it read data from interface, user has to write filter with -f (accortding to pcap-filter(7)) and when read from file user has to write filter with -Y ...
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2 answers
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Initiating Bulk TCP connections

Our company has 2 proxy servers that are running a vendor proprietary OS that is built on top of FreeBSD 11.2, we are having incidents on our business peak hours where proxy server stops accepting new ...
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My first Configuration DNS doesn't work or respond on centos

for studying purposes about TCP/IP, we should run a DNS server, i did the advised configuration, the server is runing without any erros, but when i request the server for the configured domain name ...
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Why ping don't response for long time even -W is specified?

I'm just confused with ping. As per my understanding, when I ping some IP address, it sends an ICMP message to the destination, and if there is no response, it get either "request timeout" ...
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219 views

Connection refused to connect a TCP/IP device

I'm trying to connect a TCP/IP device over ethernet adapter via ethernet cable. The connection is being seen in Network Manager and I can get output of ping command at least and I can't access a built-...
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12 votes
4 answers
2k views

Can I have a single server listen on more than 65535 ports by attaching an IPv4 address

I have a number of servers to SSH into, and some of them, being behind different NATs, may require an SSH tunnel. Right now I'm using a single VPS for that purpose. When that number reaches 65535 - ...
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2 answers
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Packet routing from docker container to host ip

I am wondering what is tbe route for a packet sent from src being the docker container with its own 'dockerised' IP, to the IP address of the VM, on which this docker process runs? Will the packets ...
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socket statistics (ss) program weird ipv6 listening socket address format

I have two services listening on TCP/IPv6 sockets, ssh and mysql. ss shows this: $ ss -tl6 State Recv-Q Send-Q Local Address:Port Peer Address:Port LISTEN 0 128 ...
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0 answers
119 views

Why do my Send-Q keep getting loaded but nothing come out of it?

I'm currently diagnosing a issue related to packet forwarding. I forward link layer packets to B network namespace and I found that B network namespace didn't reply to them, but I could curl and view ...
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1 answer
45 views

Dropping RSTs vs using NOTRACK

I'm in process building my own firewall. One can say I'm building user space TCP/IP stack. However, When Kernel receive packet that it can't identify, Kernel would send out RST + ACK (Not sure whether ...
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1 answer
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Interface with apipa (i..e. 169.254.x.x)

I have a ubuntu machine with two interfaces (eth0 and eth1). Eth0 interface has a dhcp address and eth1 has apipa (169.254.x.x) address. eth1 is not connected and eth0 is connected to a local network. ...
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0 answers
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How many times is the data packet copied before finally reaching the NIC?

On a typical linux machine, how many times would packets be copied from the application layer to all the way in its journey to the network card. I am assuming the protocol being used here is TCP/IP ...
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1 answer
152 views

Alternative to modifying /etc/hosts for dns lookup

I am a networking newb - ping cannot locate certain dns names, so I put them in /etc/hosts like this: 10.128.0.22 kafka.marathn.meso 10.128.0.31 elasticsearch.marathn.meso and then ping can find ...
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4 votes
2 answers
2k views

Why does telnet on a non existent port not directly reject, but time out?

telnet 8.8.8.8 8888 displays Trying... I was expecting, that this directly is refused. Background: When we have a NGINX reverse proxy server, it would be great, that it detects directly when the ...
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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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1 answer
551 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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2 answers
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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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2 answers
337 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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2 votes
2 answers
19k 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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3 votes
0 answers
343 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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  • 31
4 votes
1 answer
3k 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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1 vote
0 answers
60 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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  • 111
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1 answer
269 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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0 votes
1 answer
112 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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2 votes
0 answers
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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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1 vote
0 answers
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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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1 vote
0 answers
43 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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3 votes
0 answers
129 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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1 vote
1 answer
75 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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4 votes
2 answers
3k 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/sys/...
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  • 153
4 votes
1 answer
2k 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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33 votes
4 answers
107k 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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1 vote
0 answers
930 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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0 votes
1 answer
917 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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  • 1,309
2 votes
1 answer
3k 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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5 votes
1 answer
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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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1 vote
0 answers
1k 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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7 votes
3 answers
48k 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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1 vote
0 answers
100 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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1 vote
3 answers
484 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 ...
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  • 328
0 votes
1 answer
3k 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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0 votes
1 answer
736 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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0 votes
1 answer
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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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10 votes
1 answer
3k 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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2 votes
2 answers
4k 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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1 vote
3 answers
196 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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9 votes
1 answer
21k 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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1 vote
1 answer
4k 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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9 votes
3 answers
3k 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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