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

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239
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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 ...
9
votes
7answers
5k views

Loopback to forwarded Public IP address from local network - Hairpin NAT

This is a Canonical Question about Hairpin NAT (Loopback NAT). The generic form of this question is: We have a network with clients, a server, and a NAT Router. There is port forwarding on the ...
68
votes
6answers
56k 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 ...
45
votes
2answers
30k 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 ...
33
votes
7answers
17k 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 ...
47
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 ...
21
votes
6answers
9k views

CIDR for Dummies

I understand what CIDR is, and what it is used for, but I still can't figure out how to calculate it in my head. Can someone give a "for dummies" type explanation with examples?
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 ...
23
votes
5answers
14k views

Geo-DNS providers? [closed]

We've got a website visited by users mainly in the USA and UK. The site will be run on servers in both these locations. We would like to use a DNS service to direct users to the nearest server, but ...
3
votes
4answers
607 views

ssh delay when connecting

When connecting to one specific server (running Debian Lenny) it always takes about 5 seconds before it prompts me to enter a password. After login there is no noticable delay anymore. There is also ...
50
votes
11answers
99k 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" ...
42
votes
6answers
31k 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?
12
votes
5answers
56k views

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 ...
47
votes
3answers
12k 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 ...
82
votes
4answers
10k 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 ...
13
votes
4answers
4k views

Managing an application across multiple servers, or PXE vs cfEngine/Chef/Puppet

We have an application that is running on a few (5 or so and will grow) boxes. The hardware is identical in all the machines, and ideally the software would be as well. I have been managing them by ...
4
votes
1answer
5k views

How to troubleshoot latency between 2 linux hosts

The latency between 2 linux hosts is about .23ms. They are connected by one switch. Ping & Wireshark confirm the latency number. But, i dont have any visibility into what is causing this latency. ...
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?
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?
15
votes
6answers
14k views

Force local IP traffic to an external interface

I have a machine with several interfaces that I can configure as I want, for instance: eth1: 192.168.1.1 eth2: 192.168.2.2 I would like to forward all the traffic sent to one of these local ...
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 ...
14
votes
7answers
10k views

How many VLANs are too few and too many?

We're currently running a netwok of 800+ PCs and 20+ servers, the network infrastucture is along the lines of Core Switch 10Gb-> Area Switch 2GB-> Local Switch 1GB-> Desktop. All running 3Com ...
3
votes
4answers
2k views

What is the correct behaviour when Nameservers Change

I have been having some issues with a certain network supplier over unchanged nameservers making my site invisible to their customers. I wouldnt be bothered except that they are one of the largest ...
3
votes
5answers
21k views

Windows networking performance (SMB/CIFS)

Are there registry settings or other settings available to tune Windows networking (SMB/CIFS) performance? I'm trying to get maximum throughput for large file copy operations but any settings would ...
2
votes
3answers
776 views

Can I have web server on a home network with 1 public IP address? [closed]

I've got a fairly standard home network with a modem from my ISP, which is connected to a router which then provides NAT to about 3 PCs and laptops. There's a possibility to obtain one public IP from ...
58
votes
7answers
71k 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 ...
6
votes
3answers
15k views

Load balancing & NAT-ing multiple ISP connections on Linux

I have two internet connections from two different ISPs and I need to balance the traffic originating to and from my network between the two ISPs. I am using Debian GNU/Linux. My set-up is like this ...
18
votes
5answers
22k views

What are the implications of having two subnets on the same switch?

Can anyone tell me what some of the implications of having two different subnets on the same switch would be if VLANs are not being used?
3
votes
1answer
831 views

How to add a broadcast address to loopback with ifconfig on a OS/X?

I am trying to use ifconfig to turn on broadcast on my loopback interface. It currently reads: lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384 As you can see, no broadcast address! ...
0
votes
2answers
100 views

copying a file 2 connections away?

I dislike calling scp twice. I need to connect to box1 via ssh the again to boxNAME. How do i copy a file from boxNAME to my local drive? also how do i copy a file from my local drive back to ...
207
votes
15answers
12k 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 ...
64
votes
8answers
38k 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 ...
147
votes
13answers
24k 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), ...
9
votes
6answers
6k views

any good networking book recommended? [closed]

i have wanted to learn about networking and how they work. Are there books or websites that are good for them? Some things I wanted to learn about: how to write a program that works like ...
13
votes
6answers
4k views

What tool(s) can I use to simulate a WAN for HTTP traffic?

Sometimes I need to simulate a WAN environment between my client and server. I mean, specifically, from most important to least: Total bandwidth limit, Occasional long (many tens of seconds) delays ...
11
votes
7answers
10k views

Troubleshooting a “slow” network

We've all had a complaint that the "network" is "slow" at some point: might be localized to one room (switch) or one computer, might just be Internet (DNS? Browser issue?), might be just one ...
31
votes
11answers
23k 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 ...
10
votes
8answers
40k views

Windows7 - “The specified network password is not correct.” when the password is in fact correct

I have a samba server setup for some time now. It is a Hardware NAS - which unfortunately does not provide access to the Samba logs. (the exact model of the NAS is called Addonics NAS Adapter ) I ...
9
votes
3answers
4k views

What is needed to use anycast IPs?

So, there're a bunch of questions on SF about the uses and how anycast IPs are cool. My approach is something more practical. What specifically I need to have to use one of those addresses? Do I ...
8
votes
9answers
2k views

Network monitoring [duplicate]

Possible Duplicate: What tool do you use to monitor your servers? What software would you recommend to monitor a network? We have a main server which acts as a DNS among other services. And ...
24
votes
6answers
3k views

Hardware Firewall Vs. Software Firewall (IP Tables, RHEL)

TL;DR My hosting company says IP Tables is useless and doesn't provide any protection. Is this BS? I have two, co-located servers. Yesterday my DC company contacted me to tell me that because I'm ...
17
votes
7answers
2k views

Why don't more organizations use inside-to-inside NAT or similar solutions to allow NAT hairpins?

Inside-to-inside NAT aka NAT loopback solves hairpin NAT issues when accessing a web server on the external interface of an ASA or similar device from computers on the internal interface. This ...
14
votes
8answers
9k views

What is the network address (x.x.x.0) used for? [duplicate]

It appears to be common practice to not use the first address in a subnet, that is the IP 192.168.0.0/24, or a more exotic example would be 172.20.20.64/29. The ipcalc tool I frequently use follows ...
10
votes
6answers
12k views

How does geography affect network latency?

I have the option of hosting our database/web server at a managed hosting company on the East Coast (US) or one on the West Coast (US). Our company is based out of New York City, and both hosting ...
5
votes
1answer
4k views

Using dnsmasq to resolve all hosts to the same address

I'm running Ubuntu server on a computer used as a wireless AP, but this AP should resolve all DNS requests to an internal IP address rather than actually performing the lookup. I want to do the same ...
4
votes
6answers
4k views

Wireless to Wireless Transfer Slow on a Linksys WRT54GL

The Situation: When I try to transfer a file from one computer to another that are both connected via wireless on a WRT54GL (in a office) with dd-wrt firmware I often get bad speeds. In generally ...
3
votes
2answers
2k views

Debian 'ignores' /etc/network/if-pre-up.d/iptables

I want my iptables rules to automatically be loaded on startup. According to the wiki on Debian this can be done by placing a script with the name iptables in /etc/network/if-pre-up.d/ So I did, this ...
2
votes
2answers
126 views

Disable IP on bridge

OK, I'm running libvirt on my server, I have only one interface. In order to use the public IP in my VM I need to set up a bridge, everything OK so far.. But I don't want to setup an IP address on the ...
4
votes
3answers
5k views

second ip address on the same interface but on a different subnet

Is it possible in CentOS 5.7 64bit to have a second IP address on one interface (eg. eth0) - alias interface configuration - in a different subnet? Here is the original config for eth0 more ...
4
votes
2answers
1k views

syn/ack sequence number confusion

I was looking at some random traffic in wireshark and came across this (using relative seq/ack numbers): 1. myIP -> 74.125.227.96 [SYN] seq=0 2. 74.125.227.96 -> myIP ...