Networking refers to the technologies and techniques that enable the interconnection of devices and applications allowing them to communicate electronically.

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236
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5answers
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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 ...
204
votes
15answers
11k views

I've inherited a rat's nest of cabling. What now?

You know, you see pictures like below and sort of chuckle until you actually have to deal with it. I have just inherited something that looks like the picture below. The culture of the organization ...
146
votes
13answers
23k views

Why couldn't MAC addresses be used instead of IPv4|6 for networking? [closed]

I am reading up on TCP/IP and other related protocols and technologies. MAC addresses are described as being (reasonably :) unique, and as having a large possibility space (several hundred trillions), ...
78
votes
4answers
9k views

Should I quit using Ifconfig?

With the servers that mount Infiniband cards, when I use the ifconfig command, I get this warning: Ifconfig uses the ioctl access method to get the full address information, which limits hardware ...
70
votes
17answers
27k views

Should network hardware be set to “autonegotiate” speeds or fixed speeds?

We recently had a little problem with networking where multiple servers would intermittently lose network connectivity in a fairly painful-to-resolve way (required hard reboot). This has been going on ...
66
votes
1answer
7k views

What happens when you plug two sides of a cable to a single networking device?

What is likely to happen when you plug two ends of a network cable to a single switch/router? Will this create problems on the network, or just be ignored?
66
votes
6answers
52k views

Setting the hostname: FQDN or short name?

I've noticed that the "preferred" method of setting the system hostname is fundamentally different between Red Hat/CentOS and Debian/Ubuntu systems. CentOS documentation and the RHEL deployment guide ...
63
votes
8answers
36k views

How much network latency is “typical” for east - west coast USA?

At the moment we're trying to decide whether to move our datacenter from the west coast to the east coast. However, I am seeing some disturbing latency numbers from my west coast location to the east ...
57
votes
7answers
69k views

How to forcibly close a socket in TIME_WAIT?

I run a particular program on linux which sometimes crashes. If you open it quickly after that, it listens on socket 49201 instead of 49200 as it did the first time. netstat reveals that 49200 is in ...
51
votes
19answers
14k views

How do you document a network?

I'm not sure how to ask this question, since I'm not in the field. Say you're a network admin and you leave your job. How does the new guy know where to start?
49
votes
6answers
418k views

How to determine the hostname from an IP address in a Windows network?

My LAN has 50 Windows hosts. At the Windows command line I try ping to get the IP address of a running Windows machine. The question is how to get hostname of a specific IP address in the same ...
47
votes
11answers
96k views

How do I find if there is a rogue DHCP server on my Network?

What's the best approach towards determining if I have a rogue DHCP server inside my network? I'm wondering how most admins approach these kinds of problems. I found "DHCP Probe" ...
46
votes
3answers
11k views

How does IPv6 subnetting work and how does it differ from IPv4 subnetting?

This is a Canonical Question about IPv6 Subnetting. Related: How does IPv4 Subnetting Work? I know a lot about IPv4 Subnetting, and as I prepare to (deploy|work on) an IPv6 ...
45
votes
12answers
4k views

What should I pay attention to when I'm buying a network switch?

Since I'm not a hardware expert, I don't know what features make a network switch a good network switch. What should I pay attention, when I'm comparing the different models from different vendors?
45
votes
2answers
29k views

How do VLANs work?

What are VLANs? What problems do they solve? I'm helping a friend learn basic networking, as he's just become the sole sysadmin at a small company. I've been pointing him at various questions/answers ...
43
votes
7answers
3k views

Probability of Blade Chassis Failure

In my organisation we are thinking about buying blade servers - instead of rack servers. Of course technology vendors also make them sound very nice. A concern, that I read very often in different ...
43
votes
5answers
265k views

How to check if a port is blocked on Windows?

What is the easiest way to check if port 3306 on my localhost is being blocked?
42
votes
6answers
30k views

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?
41
votes
17answers
20k views

Switching to IPv6 implies dropping NAT. Is that a good thing?

This is a Canonical Question about IPv6 and NAT Related: How does IPv6 subnetting work and how does it differ from IPv4 subnetting? How can I 'dip my toes' into dynamic IPv6 ...
41
votes
3answers
1k views

Assessing equipment damage following a lightning strike - Should I have planned more?

One of my client's sites received a direct lightning hit last week (coincidentally on Friday the 13th!). I was remote to the site, but working with someone onsite, I discovered a strange pattern of ...
40
votes
4answers
15k views

How exactly & specifically does layer 3 LACP destination address hashing work?

Based on an earlier question over a year ago (Multiplexed 1 Gbps Ethernet?), I went off and setup a new rack with a new ISP with LACP links all over the place. We need this because we have individual ...
39
votes
5answers
2k views

Is there a linux terminal command that lets you see the amount of data coming in to your tcp connections in real time?

It would be something similar to top, where you see your cpu processes in real time. I'm not looking for a GUI like Wireshark to do it.
39
votes
6answers
27k views

What is the difference between a managed and unmanaged switch?

I've seen some documentation discussing the use of an unmanaged switch. What is the difference in functionality/performance/etc. between an unmanaged and managed switch?
36
votes
5answers
5k views

What is a T1 in modern terms?

I often hear this term used "We have a T1"... used on SF and other sites. I googled it and it seems like an ancient technology possibly related to frame relay but I'm not sure. Maybe things have ...
36
votes
6answers
5k views

Windows 2008 ignores Gratuitous ARP requests

We recently saw an issue after a fail over of our router where our Windows 2008 Boxes didn't start talking to the primary router after fail-back. When we did some digging they still had the ARP ...
34
votes
6answers
16k views

Why do ethernet cables have 8 wires?

This might seem a stupid question but why do Ethernet cables have 8 wires? Cat5 cables were just using 4 of the 8 wires, so only 4 are actualy 'needed'. Why not 12 or 16 wires?
33
votes
4answers
10k views

Why do consoles sometimes hang forever when SSH connection breaks?

I've seen this with so many consoles (on Linux, Mac, ...), and with lots of different machines in many different networks. I can never pinpoint the exact reason, why this happens: All you have to do ...
32
votes
7answers
16k views

What is “anycast” and how is it helpful?

I'd never heard of anycast until a few seconds ago when I read this SF post. The wikipedia entry on it is quite formal and doesn't really evoke a mental picture of how it would be used. Can someone ...
31
votes
11answers
22k views

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 ...
30
votes
4answers
104k views

Is it possible to change an “Unidentified Network” into a “Home” or “Work” network on Windows 7

I have a problem with Windows 7 RC (7100). I frequently use a crossover network cable on WinXP with static IP addresses to connect to various industrial devices (e.g. robots, pumps, valves or even ...
30
votes
3answers
809 views

Windows TCP Window Scaling Hitting plateau too early

Scenario: We have a number of Windows clients regularly uploading large files (FTP/SVN/HTTP PUT/SCP) to Linux servers that are ~100-160ms away. We have 1Gbit/s synchronous bandwidth at the office and ...
29
votes
6answers
3k views

What are .DS_Store files and why does OSX leave them on Windows shares?

Whenever I access windows shares from OSX 10.5 it leaves .DS_Store files on the remote filesystem. What are they used for, and are they necessary, and can they be prevented from being created?
29
votes
3answers
19k views

What's best practice for communication between Amazon EC2 instances?

I've been setting up Amazon EC2 instances for an upcoming project. They are all micro instances, running Ubuntu Server 64bit. Here's what I've setup so far: Web Server -- Apache Database Server ...
29
votes
8answers
27k views

Windows Server 2008 R2 network adapter stops working, requires hard reboot

TL;DR version: Turns out this was a deep Broadcom networking bug in Windows Server 2008 R2. Replacing with Intel hardware fixed it. We don't use Broadcom hardware any more. Ever. We have been ...
29
votes
3answers
4k views

Tuning iSCSI storage

This is a Canonical Question about iSCSI we can use as a reference. iSCSI is a protocol that puts SCSI commands as payload into TCP network packets. As such, it is subject to a different set of ...
28
votes
7answers
12k views

How many computers can have the same public IP?

I've got a list of hundreds of page requests from the same IP and I need to know if these could be requests by different computers.
28
votes
4answers
2k views

Is a Self Signed SSL Certificate a False Sense of Security?

Is a Self Signed SSL certificate a false sense of security? If you are being eavesdropped, the user will simply accept the certificate like he/she always does.
28
votes
8answers
8k views

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 ...
28
votes
8answers
237k views

What does “TTL expired in transit” mean on a ping attempt?

We get the message “TTL expired in transit” when we try to ping to a server in a different network segment. When we run tracert, 4 ip addresses repeat themselves indefinitely: 14 60 ms 59 ms ...
27
votes
14answers
55k views

What is a patch panel?

What is a patch panel? How it is different from (layer 2) switch? EDIT: I think my primary question (and confusion) is this: Why don't network connections go straight to the switch? Don't we still ...
27
votes
5answers
1k views

Barriers to IPv6 deployment: addressing

There are several things that are keeping IPv6 deployment from being a topic of active discussion here at my work. There are the usual technical issues, but one non-technical one appears to be a major ...
26
votes
6answers
1k views

Top-like tool for IP traffic [closed]

I need to keep watch on how much bandwidth some connections are taking in a server, and I know I have seen a top-like tool for that before. However, I can't remember the name of the tool, and I'm not ...
26
votes
3answers
2k views

Is it safe to reboot a server open to the internet?

Specifically I have an iptables ruleset defined on a server running CentOS. Am I guaranteed / can I guarantee / how can I guarantee that when networking comes online (either at machine boot, or after ...
25
votes
9answers
3k views

How can I force users from USA to go the USA server and visitors from UK to go to the UK server

If I have a single domain with visitors from both USA and Europe and also have 2 servers, one in USA and one in UK, how can I force users from USA to go the USA server and visitors from UK to go to ...
25
votes
7answers
3k views

MITM attacks - how likely are they?

How likely are "Man in the Middle" attacks in internet security? What actual machines, apart from ISP servers, are going to be "in the middle" of internet communications? What are the actual risks ...
25
votes
10answers
11k views

Network cable color conventions? [closed]

Are there any color conventions for network cable? I'm talking jacket color here, not the color of the individual conductors. I've seen and used mostly grey and blue which is what's usually readily ...
25
votes
7answers
2k views

Puppet Security and Network Topologies

Background: I am finally setting aside some time to join the 21st Century and look at Puppet. As it stands today we version control all server configurations in a repository that is held internally ...
24
votes
5answers
4k views

Locate rogue DHCP server [duplicate]

Possible Duplicate: How do I find if there is a rogue DHCP server on my Network? I know this is a serious long shot, but here we go. In the past week or so, for users connected to a ...
24
votes
15answers
2k views

How much is IP V6 addressing being used?

Just how much IP V6 addressing is really in typical use out there? I see that Linux/UNIX seems to be ready for this. But I don't see the readiness as much as the Windows side. Especially not for ...
24
votes
1answer
3k views

How should I set up my Fibre Channel (FC) network?

How do FC switches work, and how should I configure mine?