TCP and IP are two important protocols used in networking today. Due to their importance, the Internet Protocol Suite is also commonly known as "TCP/IP"

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How does IPv4 Subnetting Work?

This is a Canonical Question about IPv4 Subnets. Related: How does IPv6 subnetting work and how does it differ from IPv4 subnetting? How does Subnetting Work, and How do you do it ...
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6answers
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Is X.Y.Z.0 a valid IP address?

Are IP addresses with a 0 in the last octet valid? 10.6.43.0 In my case, I have the the following netmask 255.255.252.0 What about a 0 for the other octets?
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5answers
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Huge amount of TIME_WAIT connections says netstat

Okay, this is creeping me out - I see about 1500-2500 of these: root@wherever:# netstat Proto Recv-Q Send-Q Local Address Foreign Address State tcp 0 0 ...
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11answers
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What is the difference between UDP and TCP?

My router has two protocols (and a "both" option) that I can select when setting up port forwarding: UDP and TCP. What is the difference between these two protocols and when would you select one over ...
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6answers
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When IP aliasing how does the OS determine which IP address will be used as source for outbound TCP/IP connections?

I have a server running Ubuntu Server with four IP addresses aliased on a single NIC. eth0 192.168.1.100 eth0:0 192.168.1.101 eth0:1 192.168.1.102 eth0:2 192.168.1.103 (Using ...
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2answers
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Serial port forwarding over TCP/IP (linux server)

I am looking for a way to use a remote serial port on a linux machine over LAN. The machine is running ubuntu 10.04 and I have a arduino board connected to it, that I would like to be able to ...
29
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3answers
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Tuning Linux IP routing parameters — secret_interval and tcp_mem

We had a little failover problem with one of our HAProxy VMs today. When we dug into it, we found this: Jan 26 07:41:45 haproxy2 kernel: [226818.070059] __ratelimit: 10 callbacks suppressed Jan 26 ...
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8answers
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When/why to start subnetting a network?

Under what conditions does one start to consider subnetting a network? I'm looking for a few general rules of thumb, or triggers based on measurable metrics that make subnetting something that should ...
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5answers
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In Windows, using the command line, how do you check if a port is open?

I want to see if traffic gets through on a specific port on another machine. Is there a simple way to test for this?
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9answers
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What is the OSI model and how does it apply to todays networks?

As a system administrator what should I know about the OSI model? (Rec X.200) Briefly, what are the layers and what do they do? How much do I need to know about in my day-to-day work? How does this ...
16
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2answers
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Unix socket vs TCP/IP host:port

Could someone please describe to me the pros and cons of using a Unix socket file vs a tcp/ip localhost:port when setting up services on a server (Ubuntu, FWIW)? In this particular instance it's for ...
12
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2answers
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Which is the default TCP connect timeout in Windows?

Which is the default TCP connect timeout in Windows? There is a registry key to configure it or it's set dynamically?
11
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2answers
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Multiple IP addresses per NIC

How can I have multiple IP addresses assigned to a single NIC? I remember doing this on Unix way back when. Can it be done on Windows?
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4answers
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How to automatically assign a route to client in Windows Server PPTP VPN?

Is there a way to configure PPTP VPN on Windows Server which automatically tells the client to add a route for the private network? I have to do it manually on every PC (once) using following command ...
2
votes
3answers
3k views

Shaping outbound Traffic to Control Download Speeds with Linux

I have a situation where a server makes lots of requests from big webservers all at the same time. Currently, I have not control over the amount of requests or the rate of the requests from the ...
5
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2answers
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Answering on the same interface where the request came from

First, I know this is not how IP is intended. But as usual, this is how I need to have it working. I work for a security company. There are at least 2 network interfaces. Both interfaces should have ...
4
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2answers
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UNC Path fails by IP “no network provider accepted the given network path”, but works using hostname

I have an unusual problem with a Windows Server 2003 (Standard x86) box. It appears the machine will not accept connections to its shares (locally and from other domain member servers) by using its ...
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3answers
2k views

Too Many ESTABLISHED connection from a single IP address in Apache

netstat -ntp |grep 80 shows too many ESTABLISHED connection from single IP address. Around 300 of them and it is not an attack and user is using a 2G connection to access Apache. This is the case ...
7
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1answer
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limits.conf setting doesn't 'stick'

Trying to get the equivalent of ulimit -n 20000 on a high load web server, however the /etc/security/limits.conf on ubuntu hardy doesn't seem to stick. here is what I set in the config file. root ...
5
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10answers
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Forward port to another Ip/port

I recently found out that my ISP disables port 135. I have a server and personal computer behind my router. A friend and I are working on a programming project and are running into some sql issues ...
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2answers
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How do I set up IP over FC?

I have 2 systems, with a Broadcom BCM5701 and a LSI7202p, of which are connected with a LC->SC cable. The cards are properly detected in Linux, however I wish to set up IP over FC. I've read online ...
33
votes
11answers
8k views

Why would you use IPv6 internally?

Of course, I realize the need to go to IPv6 out on the open Internet since we are running out of addresses, but I really don't understand why there is any need to use it on an internal network. I have ...
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6answers
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Looking for an open source real-time network analysis program

Can somebody recommend an open source real-time network analysis program? What I'm looking for the program to do is display a graph of bandwidth usage by IP within our internal network that can ...
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3answers
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How are IP addresses actually assigned?

I'm having a hard time understanding how a governing body assigns IP addresses, companies use BGP to advertise those IPs, and how the internet works. Then, where the hell does DNS come in? Can ...
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6answers
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How do I view the TCP Send and Receive Queue sizes on Windows?

Linux netstat shows send and receive queue sizes. How do I get this info under Windows, specifically Server 2003?
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2answers
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How do I fake dropped packets (or actually make them fail)?

Background One of our clients suffers from an intermittant problem with their internet where it will drop packets when a user downloads a large file (their IT is looking into the problem). I have ...
4
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2answers
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How Can I Harden the TCP/IP Stack in Windows Server 2008? [duplicate]

I would like to make sure that my Windows 2008 servers are hardened against DDOS attacks. There is a Microsoft Technet article on Hardening the TCP/IP stack, but it was last revised in January 2006. ...
5
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4answers
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Running lsof -i shows a lot of connections in CLOSE_WAIT ? Should I worry

So I am running lsof -i | wc -l periodically and it is telling me that out of 420 lines, between 240 and 255 are in CLOSE_WAIT state. How does TCP connections enter this state ? Should I be worried ...
3
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2answers
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IIS7 hundreds of connections in CLOSE_WAIT

I have a .Net application on my IIS7 server it was working fine until I had to move it to another server. I moved the exact same code to the new server and I noticed that after some hours the ...
3
votes
3answers
8k views

How to increase MTU size on Linux 2.6?

How to increase MTU size on Linux 2.6? Is such a thing possible? If yes, which files (in /etc or elsewhere) must one edit?
2
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2answers
3k views

Specifying a preferred route when there are multiple links to same network

I have a server with multiple interfaces and IP addresses on the same network. I would like for non-iSCSI traffic to exclusively use one of the interfaces, and for iSCSI traffic to exclusively use the ...
2
votes
5answers
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How to extend IP Range from 192.168.1.1 to 192.168.2.254

Here's my question. I currently have a network setup to have Static IP manually assigned between 192.168.1.1 and 192.168.1.99 and the rest (192.168.1.100 through 192.168.1.254) assigned automatically ...
4
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3answers
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Are there simpler ways to do traffic shaping in linux besides tc?

I read lartc but I don't feel I need such a complicated solution for simple needs. One of such simple use cases is to limit a specific process' available bandwidth, upstream or downstream. How can I ...
3
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2answers
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How to get a service to listen on port 80 on Windows Server 2003

I've coded a custom windows service that listens on TCP port 80 but when I try to install it on a Windows Server 2003 machine it fails to start because some other service is already listening on that ...
3
votes
6answers
853 views

TCP Sessions and IP Changes

What happens to a TCP session when the IP of a client changes? I did a simple test of having netcat listen on a port, and connecting to that port from a client machine. I then changed the IP of ...
2
votes
4answers
6k views

Ethernet Loopback plug - running a ping

For a project at work, I need to be able to test various Ethernet NICs by connecting them to a "loopback adapter plug", like this one on various embedded Linux boxen that come off a production ...
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4answers
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Error Connection to SQL Server using [HOSTNAME]\instance or [FQDN]\Instance, [IP]\instance working

This one's kind of weird, at least to me. I've got MSSQL server 2k5 (STD) installed on Server 2k3 R2 SP2 (on account of some legacy software that doesn't yet support x64 or Server 2008), using ...
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2answers
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Is there a limit to how many sites can be hosted on a single IP address when using HTTP Host Headers on Windows 2008?

For reasons that are lost in the mists of time, our older Windows (2000, 2003) servers have been configured with a "Administrative" IP address and three further "Hosting" IP addresses. There are also ...
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2answers
489 views

Static IP for dynamic IP

I have a dynamic IP address. I would like to have a static IP, but Virgin Media don't allow static IPs for residential broadband services, even if you ask them really nicely and offer to pay for it ...
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1answer
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Windows XP TCP/IP No buffer space available

I have isolated a problem down to this: On Windows XP Pro, SP2 if one does an experiment where one tries to open TCP/IP sockets in a loop (bascially, listen port 7000, listen port 7001, etc.) After ...
0
votes
1answer
106 views

TCP/UDP Connection States documentation

Does anyone know where to find documentation for TCP/UDP connection states? Preferably non-Microsoft with unix backing. Basically, I'm looking for more information about TCP established, TCP ...