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

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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 ...
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2answers
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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?
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2answers
876 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?
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17answers
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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 ...
61
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3answers
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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?
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What is the best way to transfer a single large file over a high-speed, high-latency WAN link?

This looks related to this one, but it's somewhat different. There is this WAN link between two company sites, and we need to transfer a single very large file (Oracle dump, ~160 GB). We've got full ...
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6answers
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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?
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4answers
111k 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 ...
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3answers
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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 ...
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4answers
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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 ...
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5answers
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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.
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What's the difference between a switch, a router, and a modem?

What's the difference between a switch, a router, and a modem?
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8answers
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What tools can create a map of my network?

This is a Canonical Question about network mapping software. Are there any good network mapping tools for creating a visual representation of the network? I'm talking about an automatic mapping ...
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6answers
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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?
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5answers
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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 ...
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11answers
37k 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 ...
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9answers
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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 using ...
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1answer
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MySQL [Warning] IP address could not be resolved

I'm running MySQL5.6.3 on a CentOS 6.1 virtual machine running on Windows XP in VirtualBox. The network card is configured in bridge mode, so my physical & virtual machines share the same ...
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9answers
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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 ...
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6answers
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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 ...
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4answers
30k 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
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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 ...
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3answers
9k 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 ...
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17answers
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Inexpensive Network Monitoring tools for Windows

I'm looking for a free or inexpensive Windows-based network monitoring tool for a small network. I'm familiar with Nagios, but we run a Windows-only shop and I don't want one oddball Linux machine to ...
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2answers
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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, I'...
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8answers
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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 ...
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4answers
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Traffic Management recommendations [closed]

What's your strategy towards traffic prioritization/management. I am not really to just get a list of packet shaping solutions. Instead, I would like to get recommendations about traffic management ...
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2answers
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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 ...
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1answer
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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 ...
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9answers
18k 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 ...
45
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8answers
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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 ...
17
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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 ...
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3answers
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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 ...
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5answers
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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 ...
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4answers
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How do you PREPEND an iptables rather than APPEND?

Pretty basic question.. How do you PREPEND an iptables rather than APPEND? I have DROP statements at the bottom of my rules. I have software to add new rules but adding rules after DROP statements ...
18
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2answers
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Are there any advantages to using someone else's publicly-routable IPv4 addresses locally?

My 10000+ users network, which spans the whole State and is very complex, has a "strange" addressing scheme. Though our PCs are not directly connected/exposed to the Internet, our network designers ...
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2answers
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Bridging LXC containers to host eth0 so they can have a public IP

UPDATE: I found the solution there: http://www.linuxfoundation.org/collaborate/workgroups/networking/bridge#No_traffic_gets_trough_.28except_ARP_and_STP.29 # cd /proc/sys/net/bridge # ls bridge-...
3
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1answer
2k views

Limit/Throttle per user OpenVPN bandwidth using TC

I have a group of users connecting to my server via OpenVPN TCP and UDP (2 services). The two services are operating on tun0 and tun1 I'd like to be able to limit each user's bandwidth to say 5mb/s ...
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3answers
974 views

NetBIOS “free” network?

I was wondering if someone here has had an enterprise experience running a "NetBIOS-free" network. I have in mind a mid to big Windows-based network. I found some good posts here, here and here. I ...
8
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2answers
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iptables | Types of ICMP: which ones are (potentially) harmful?

I read that certain types¹ of ICMP packets can be harmful. Questions: Which ones and why? How should I layout an iptables ruleset to handle each type of ICMP packet? Should I rate-limit any of these ...
5
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2answers
7k views

Can't ping multihomed Linux machine on non-default interface

I have a multihomed Ubuntu server with a set of interfaces that includes: eth2: 10.10.0.131/24 eth3: 10.20.0.2/24 The default interface is eth2, with a gateway of 10.10.0.1. Here's what the routing ...
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2answers
6k views

Setting up two NICs on two separate LANs provides error

I wish I had found this before starting in, but it's too late for that... I am running CentOS 5.5. I started following this guide for setting up two NICs on different networks. Everything was ...
23
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4answers
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1 Year DHCP Lease

Just a little background I'm a fairly young I.T. Tech working in a school only and only been working in the as a technician for a few years so I would still consider myself a "newbie" Anyway, My boss ...
15
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3answers
49k views

How to setup a MySql server to accept remote connections?

I am installing a MySql server in Ubuntu desktop. I could connect MySql Query Browser to it when specifying the Server Hostname as localhost, but when I replace it by the machine's IP it stops working ...
14
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5answers
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Is there a way to get wireshark to capture packets sent from/to localhost on Windows?

Is there a way to get wireshark to capture packets sent from/to localhost? When I monitor traffic going from my computer to another, or from another computer to my computer, then it works. But ...
13
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4answers
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Hardware firewall vs VMware firewall appliance

We have a debate in our office going on whether it's necessary to get a hardware firewall or set up a virtual one on our VMWare cluster. Our environment consists of 3 server nodes (16 cores w/ 64 GB ...
8
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2answers
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What does limit performance of scp?

I've two Debian Linux machine connected via 1 Gbit LAN. I can measure this with a raw HTTP file transfer with wget which gets around 100MB/s in either direction. When I now use scp, the maximum ...
5
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5answers
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How can I get BIND and Microsoft DNS to work together well?

I would like to try and move as much of our company DNS config into BIND, because I find it easier to work with, but having Active Directory means we have to have at least the domain's zone in ...
5
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3answers
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Defining a persistent static route on Mac OS X

How does one define a static route on MacOS X which persists through reboots? The only suggestion I've found on Google advises setting up a launchd service to run at boot, which seems like a horrible ...
2
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1answer
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How to ignore a set of Mac addresses in dhcpd.conf?

Is it possible in dhcpd.conf to ignore requests from a set of MAC addresses? Something like this: host vminstances { hardware ethernet d0:0d:*; ignore booting; }