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

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1answer
13k 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 ...
8
votes
4answers
14k 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 ...
7
votes
3answers
20k views

What is DNS Delegation?

In an answer to my previous question I noticed theses lines: It's normally this last stage of delegation that is broken with most home user setups. They have gone through the process of buying a ...
15
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6answers
18k 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 ...
7
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2answers
4k 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 ...
4
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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 ...
2
votes
2answers
152 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 ...
5
votes
1answer
24k views

iptables forwarding between two interface [closed]

So I have a linux box with two wireless interfaces, one is a station and the other an AP. wlan0 (station) - Connected to the internet connection wlan1 (AP) - Other clients connect to it. I would ...
4
votes
2answers
383 views

How do I force all devices on a network to register with IT before connecting, without vulnerability to Static IP-ing or MAC spoofing?

Context: I'm an admin for a midsize corporate network with several overlapping wireless access points and an ethernet cabling infrastructure. To comply with a security audit, we were recently ordered ...
4
votes
2answers
2k 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 ...
4
votes
5answers
26k views

Unable to Telnet into port 25 on CentOS PostFix Server

I'm trying to telnet into port 25 on a CentOS server that runs PostFix to test sending email messages from the server. When I try to telnet in from another CentOS box on the same network I get the ...
3
votes
2answers
2k views

Reserve a single ip for a wired and wireless NIC of the same machine

I'm using w2k3 dhcp server, and I've reserved an IP adress for my laptop to facilitate port forwarding. I previously had a pure wired network, but I just added a WiFi router to this network for the ...
1
vote
5answers
1k views

vSwitch configuration with 12 uplinks

I have been doing a lot of research on vSwitch configurations, but I think I am more confused now after all of the reading that I have done. So here is my situation 3 ESX Hosts (12 nics each), 1 ...
1
vote
2answers
3k views

how to request/acquire all records from a DNS?

I want to see what nodes exist under a certain domain from within the domain. Short of querying every valid ip address within that domain, is there a way to get all records/map the network?
0
votes
5answers
7k views

Monitor file copies with SCP done via SSH

Is there a way to keep a log of the files copied using SCP? I am administering a server which contains some files that should be monitored (in a specific folder and its subfolders), so when someone ...
0
votes
2answers
857 views

is it possible to direct connect a client and server with 10GBASE CX4 copper cables?

Server has two 10GBASE-CX4 ports. client has 10GBASE CX4 HBA. can theybe directly connected with a CX4 cable without the need for a switch? like SAS Infiband connectors?
78
votes
17answers
48k 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 ...
60
votes
3answers
416k views

How to check if a port is blocked on a Windows machine?

On the Windows platform, what native options to I have to check if a port (3306, for example) on my local machine (as in localhost), is being blocked?
28
votes
6answers
75k views

Improving TCP performance over a gigabit network with lots of connections and high traffic of small packets

I’m trying to improve my TCP throughput over a “gigabit network with lots of connections and high traffic of small packets”. My server OS is Ubuntu 11.10 Server 64bit. There are about 50.000 (and ...
34
votes
3answers
27k 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 ...
48
votes
6answers
286k views

In Windows, using the command line, how do you check if a remote port is open?

What is a simple way in Windows to test if traffic gets through to a specific port on a remote machine?
42
votes
8answers
18k 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 ...
38
votes
4answers
102k views

VirtualBox: How to set up networking so both host and guest can access internet and talk to each other

I was wondering if someone could give me a simple guide on how to set up virtual networking in VirtualBox (4.0.2) so that the following scenarios work: Both Host and Guest can access Internet Host ...
23
votes
4answers
13k views

Why do people tell me not to use VLANs for security?

As per title, why do people tell me not to use VLANs for security purposes? I have a network, where a have a couple of VLANS. There is a firewall between the 2 VLANs. I am using HP Procurve switches ...
19
votes
3answers
24k views

How to use Bonjour?

First, what exactly Bonjour does (pleas read my guesses written bellow)? Here I found out that Bonjour enables automatic discovery of computers, devices, and services on IP networks. But I thought ...
10
votes
4answers
36k views

Best way to segment traffic, VLAN or subnet?

We have a medium-sized network of around 200 nodes and are currently in the process of replacing old daisy-chained switches with stack-able or chassis style switches. Right now, our network is broken ...
42
votes
5answers
3k 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.
22
votes
4answers
25k views

Docker containers can't resolve DNS on Ubuntu 14.04 Desktop Host

I'm running into a problem with my Docker containers on Ubuntu 14.04 LTS. Docker worked fine for two days, and then suddenly I lost all network connectivity inside my containers. The error output ...
14
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4answers
16k views

What's the difference between a switch, a router, and a modem?

What's the difference between a switch, a router, and a modem?
26
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 ...
52
votes
6answers
66k 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?
45
votes
5answers
26k 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 ...
31
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9answers
38k 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 ...
18
votes
7answers
35k views

traceroute TCP equivalent for Windows [closed]

I'm trying to determine where connectivity to an external host using a specific TCP port is being blocked. Traceroute for Windows only uses ICMP, and telnet will only tell me that the port is blocked ...
28
votes
8answers
39k views

Does using a single cable to connect two switches create a bottleneck?

I realise this may be a stupid question for some, but it's something I've always wondered about. Let's say we have two gigabit switches and all of the devices on the network are also gigabit. If 10 ...
14
votes
7answers
47k views

How to tell if it's your problem or your ISP's problem

I originally titled this "how to tell if your internet is down or your network is just screwed up" and Jeff's AI said that this questioned would probably be closed. Nevertheless, someone here is ...
22
votes
4answers
28k views

How does Windows decides which DNS Server to use when resolving names?

What algorithm does Windows use to decide which DNS Server it will query in order to resolve names? Let's say I have several interfaces, all active, some with no dns server specified, some told to ...
19
votes
4answers
2k views

Slow Transfers over Distance

From our NY Datacenter, transfers to locations that are farther away are having poor performance. Using speed test to test various locations, we can saturate our 100 mbit uplink to Boston and ...
12
votes
2answers
3k views

VMware Distributed vSwitches (VDS) - Design, theory, *real* use cases and examples?

I'm starting to explore VMware Distributed Switches (dvSwitches or VDS) for use in existing and new installations. Assume VMware version 5.1 and newer with Enterprise Plus licensing. Prior to this, ...
9
votes
8answers
18k views

How to prevent a LOIC (DDOS) attack? [duplicate]

The program LOIC (in the news a lot the last days) causes a lot of damage. What can I do on my server to prevent this kind of attacks? Auto-block ip when receive a strange connection? Because mostly ...
20
votes
1answer
2k views

Under what circumstances is TCP-over-TCP performing significantly worse than TCP alone (2014)?

Many admins keep perpetuating - on ServerFault and elsewhere - how bad of an idea TCP-over-TCP is, e.g. in VPNs. That even the slightest packet loss will make one suffer from at least severe ...
5
votes
6answers
4k views

Encrypting absolutely everything, even within the LAN

Has anybody tried that approach already? I'm really considering it: Instead of relying on network based IDS etc., every packet must use encryption which was initiated by a certificate issued by my own ...
3
votes
2answers
7k views

how to calculate packet loss from a binary TCPDUMP file

Our connection to just one remote server on port 80 over the internet is not working properly. (From time to time it is working and sometimes not) It must be some kind of packet loss, because from ...
19
votes
9answers
17k views

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 ...
17
votes
3answers
2k views

Is it possible to SSH access a server with a misconfigured subnet?

We have a server where one of our engineers misconfigured the subnet and now we are locked out of this server and the only access that I know of would work is a serial console from IDC (it means ...
12
votes
3answers
7k views

Networking Units: Not getting expected performance from 100Mb Ethernet

Our company has a brand new NAS, and the idea is that we will be able to use it for fast, shared access to our data on our network. It's a fairly simple 2-disk system, but from what I understand, it ...
10
votes
3answers
1k views

Creative IP/subnet/dns schemes

I've only administered rather small networks (<=25 nodes). Usually I put the gateway .1, dns/proxy as .10, mail at .20, printers at .30-39 and so on and so forth. I never directly use IP addresses ...
29
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5answers
10k views

Can TCP and UDP packets be split into pieces?

Can TCP packets arrive to receiver by pieces? For example, if I send 20 bytes using TCP protocol, can I be 100% sure that I will receive exactly 20 bytes at once, not 10 bytes then another 10 bytes ...
12
votes
3answers
9k views

Persistent ip rule on Linux (Redhat)

How can I configure a persistent ip rule on Linux (specifically Redhat based distros)? Is there no built in method? Is my only option adding to /etc/rc.d/rc.local or creating my own rc.d script? ...
11
votes
7answers
491 views

Truly understanding networking?

I understand the basics of networking such as Lan and stuff. I know what many of the protocols are and how to build a client/server socket program in C. But what I really want is a very good ...