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

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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 ...
8
votes
8answers
371 views

Macintosh gotchas

Up until now, I've only managed networks with Windows users and the occasional *nix server. Soon, a few users with Macs will get added to our network. What are some "gotchas" to look out for when ...
7
votes
3answers
7k views

TIME_WAIT connections not being cleaned up after timeout period expires

I am stress testing one of my servers by hitting it with a constant stream of new network connections, the tcp_fin_timeout is set to 60, so if I send a constant stream of something like 100 requests ...
27
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5answers
27k views

How to _MOVE_ files with scp?

How to not copy but move files from one server to another (both Linux)? man scp didn't give me anything useful. I cannot use 'scp' then 'rm' because I must make sure the file is successfully ...
19
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4answers
15k views

What is the “in-the-wire” size of a ethernet frame? 1518 or 1542?

According to the table here, it says that MTU = 1500 bytes and that the payload part is 1500 - 42 bytes or 1458 bytes (<- this is actually wrong!). Now on top of that you have to add IPv4 and UDP ...
19
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4answers
36k views

System error 1219 has occurred

I am trying to connect to a remote server and deploy a service there, through a deploy script. I start by stating "Net use" and send the credentials for the server. But here I get system 1219 error: ...
17
votes
2answers
1k views

What is the fall off of subsecond throughput on Ethernet Network Interfaces

On a network interface, speeds are given in term of data over time, in particular, they are bits per second. However, in the uber-fast world of computing -- a second is kind of a really long time. So ...
13
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2answers
19k views

Windows Appending Domain Suffix To All Lookups

I have a reoccurring DNS problem that has been plaguing our users occasionally causing their laptops to appended our companies domain to the end of all DNS queries. The problem only occurs when users ...
13
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4answers
33k views

Is there an equivalent command for 'init.d/networking restart' in OS X

From time to time, I've encountered issues with OS X clients' network connections (Wired and Wireless, Leopard/Snow Leopard) where nothing will fix the issue, until you reboot. Is there a ...
10
votes
4answers
11k views

10GbE sfp+ cross over cable required? Is there such a thing?

To preface, this is my first experience with 10GbE networking and I have encountered an issue which my research does not seem to locate a solution for... I have two servers (older DL580G5 and DL380G5)...
8
votes
6answers
23k views

Is it possible to match an internal IP address to a switch port?

I'm trying to find a computer that has a certain IP address on our internal network. I have identified the computer name from DNS, but in this case it does not help me. Just wondering if I can ...
8
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2answers
8k views

ip address scope parameter

In Linux, the command ip address add [...] has a scope argument. The man page says that the scope is "the scope of the area where this address is valid". Follows the list of legal scopes: global ...
7
votes
9answers
3k views

LAN Between Buildings

Right now I have two buildings across the street from one another that both have typical consumer aDSL connections (something like 12 Mbs down/1 Mbs up). When I need to access resources on the other ...
6
votes
3answers
8k views

Bonding 2 or more Gigabyte NIC together to get 2Gbps performance between 1 server and 1 client?

I have not gotten the server or the NIC yet, but here is the target setup: 1x Server 1x Client 1 or more NIC linked point to point between the Server & Client (No switch involved) So I am ...
5
votes
5answers
9k views

How to get Wake-on-LAN working?

I have a PC behind a router with a dynamic IP address that I want to configure for wake-on-LAN. How do I send the magic packet to the PC? Do I configure my router to forward UDP port 6 to the PC? How ...
5
votes
6answers
1k views

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 ...
17
votes
3answers
3k views

How does network sniffing software work over a switch?

We have several of standard non-managed 3com switches in a network. I thought switches were supposed to only send packages between peers of a connection. However it appears network sniffing software ...
16
votes
1answer
291 views

Vendor whitepaper says: 5Mpps no prob. I'm already hitting a wall at 120kpps. Where's the bottleneck?

HP's whitepaper on their QLogic (fka Broadcom) NetXtreme II adapters, which includes the specific NIC that I'm testing, states (page 7) that their small packet performance for packets up to 256 bytes/...
16
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3answers
17k views

Maximizing rsync performance and throughput - directly-connected gigabit servers

I have two Dell R515 servers running CentOS 6.5, with one of the broadcom NICs in each directly attached to the other. I use the direct link to push backups from the main server in the pair to the ...
13
votes
5answers
39k views

How to configure DNS on Windows with multiple NICs?

I have two network adapters on my PC each connected to a different network (one LAN and one Wireless). I set up routing tables to have some of the addresses routed to the LAN and others to the ...
10
votes
10answers
37k views

How to use a Tone Generator to trace a network cable

We have a tone generator kit for tracing network cables, but I am having trouble using it correctly. The tone generator end plugs into the network cable I am trying to trace, and then I assume I ...
10
votes
3answers
12k views

iftop - how to generate text file with its output?

iftop is great tool to view almost live bandwidth usage distinguished by source-ip source-port destination-ip destination port. I'm using it to see which client's ip is using most bandwidth. Now I ...
9
votes
4answers
10k views

Max number of socket on Linux

It seems that the server is limited at ~32720 sockets... I have tried every known variable change to raise up this limit. But the server stay limited at 32720 opened socket, even if there is still 4Go ...
7
votes
5answers
11k views

Network port open, but no process attached?

I have a weird situation going on with an open network port. My main question is, why would there not be a program associated with an open TCP port: netstat -ln --program Active Internet connections (...
7
votes
2answers
5k views

VLAN for WiFi traffic separation (new to VLANing)

I run a school network with switches in different departments. All is routed through to a central switch to access the servers. I would like to install WiFi access points in the different departments ...
7
votes
3answers
33k views

What does “incoming” and “outgoing” traffic mean?

I've seen many resources explaining how to set up a server's firewall to allow incoming and outgoing traffic on HTTP standard ports (80 and 443), but I can't figure out why I would need either of them....
7
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3answers
2k views

Does routing distance affect performance significantly?

When I say routing distance, I mean on a global scale. For instance, if my target audience is in China, do I look for a host within China?
6
votes
1answer
4k views

Upgrading from 100BASE-FX to 1000BASE-SX fiber?

I've been trying to upgrade our small fiber network from 100BASE-FX to 1000BASE-SX. The cables are 62.5/125 multimode fibers, all terminated in patch panels with ST plugs (the round ones). As I ...
6
votes
7answers
4k views

Static IP Address assignment vs DHCP address assignment

I manage a small-ish network that consists of less than 70 nodes. The previous system administrators opted to have a dhcp server and manually set dhcp addess. I have opted to rather use dhcp ...
5
votes
4answers
1k views

dead man's switch for remote networking interventions on Linux

As I'm going to change the network configuration of a remote server, I was thinking of some security mechanisms to protect me from accidentally losing control on the server. The level-0 protection I'...
5
votes
5answers
11k views

Mass installation on networked Windows computers?

Hey guys, I'm currently managing a network of around 15 computers, all using Windows XP. I'm a novice Windows network admin and I'm just wondering how I would push software to all the computers in one ...
5
votes
2answers
3k views

Cheap way to detect client round trip times for http

I am trying to figure out a way to detect round trip times for each IP that connects to port 80 on my server. What is a good way to do this? There are far to many connections, and pinging each ip is ...
5
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2answers
8k views

Low latency TCP settings on Ubuntu

There is a server for measurements running on Ubuntu in my lab . And there is C program, which receives data through TCP connection and should as soon as possible send a reply. Network latency when ...
5
votes
5answers
11k views

How do I know what processes are using the network?

Sometimes I can see heavy usage of network in my Gnome System Monitor. I wonder what process is downloading/uploading data. Is there any tool which can show me: what processes are using the Internet ...
4
votes
4answers
11k views

Debian interfaces file - ignore gateway and dns entries from dhcp

In gentoo, this is as simple as: dhcp_ethX="nodns nogateway" How should I go about this in the interfaces file?
4
votes
2answers
3k views

Second ENI in AWS VPC is not accessible on Ubuntu instance

I'm just getting into VPC, trying to understand how everything works. So far the biggest hurdle I've run into is that any time I add a second Elastic NIC to a machine, that second IP is not accessible ...
3
votes
2answers
6k views

KVM/Libvirt bridged/routed networking not working on newer guest kernels

I have a dedicated server running Debian 6, with Libvirt (0.9.11.3) and Qemu-KVM (qemu-kvm-1.0+dfsg-11, Debian). I am having a problem getting bridged/routed networking to work in KVM guests with ...
3
votes
1answer
14k views

How can I detect a DDoS attack using pfSense so I can tell my ISP who to block? [duplicate]

Last week my network was hit by a DDoS attack which completely saturated our 100 MBps link to the internet and pretty much shut down all the sites and services we host. I understand (from this ...
3
votes
2answers
1k views

active directory + squid planning for a large network with over than 7000 users

We have about 1600 active nodes and 6000 students in our network and we have a great Cisco backbone, we have 8 faculties (they have sites and wireless access points) and 10 centers like hospital. We ...
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3answers
3k views

how to completely disable ipv6 on Ubuntu 9.04

what i have done: /etc/modprobe.d/blacklist.conf blacklist net-pf-10 blacklist ipv6 /boot/grub/menu.lst title Ubuntu 9.04, kernel 2.6.28-15-server kernel /boot/vmlinuz-2.6.28-...
16
votes
2answers
38k views

Does traceroute use UDP or ICMP or both?

When I do a trace on the www.google.com domain from my laptop, am I using icmp or udp ? I thought it was icmp type 11 but while searching for something else I came across rules where icmp type 30 was ...
14
votes
4answers
1k views

Linux Networking - “ip X” instead of ifconfig/route/etc?

I'm used to using commands such as ifconfig, route and so forth on linux to check and change network information. However I know there is an ip command (with various subcommands). I heard somewhere ...
13
votes
7answers
10k views

Why is it a bad idea to use multiple NAT layers or is it?

The computer network of an organization has a NAT with 192.168/16 IP address range. There is a department with a server that has an IP address 192.168.x.y and this server handles hosts of this ...
13
votes
5answers
24k views

Disable Windows Server Network Locations

I'm not sure what exactly this feature is called. But in Windows Server 2008, it has the Vista Public/Private/Domain locations. This makes sense for laptops, and none at all for servers. My problem ...
12
votes
3answers
40k views

How to broadcast ARP update to all neighbors in Linux?

Some clients in the subnet has cached the IP with old MAC address, I want them to update the new value by doing a ARP broadcast, is it possible in Linux?
11
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10answers
14k views

Is there any reason to have 2 NICs on a server?

Is there any reason to have 2 NICs on a server BESIDES the following cases? You need to connect to 2 different physical networks Redudancy (1 NIC fails, so you use the other) Are there any other ...
9
votes
4answers
2k views

Linux to Linux, 10 TB transfer?

I've looked at all the previous similar questions, but the answers seemed to be all over the place and no one was moving a lot of data (100 GB is different from 10 TB). I've got about 10&...
9
votes
4answers
33k views

Can't resolve host through VPN connection from Mac OS X [closed]

The Preamble I set up a VPN connection from my Macbook, and it seems to connect successfully. However, I can't access my work computer because hostname doesn't get resolved: $ ping myusername ...
9
votes
1answer
20k views

What exactly is the MTU/MRU issue, what it is caused by and how to fix it?

In cases of hanging, freezing, slow, unresponsive internet connections the cause is usually unreasonably identified as "MTU/MRU issue" with several hastily proposed "magic cures" (usually invalid or ...
9
votes
7answers
38k views

Why are my HyperV VM's randomly losing connectivity?

I have a strange intermittent connectivity problem happening about once every two weeks. First my configuration: I am running a HyperV failover cluster with two physical hosts (node01 and node02). ...