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

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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 ...
12
votes
5answers
6k views

I'm designing a system to handle 10000 TCP connections per second, what problems will I run into?

I have a relatively new 8-core box running CentOS. I would like to develop a stats server that uses TCP. It's very simple, it accepts a TCP connection, increments a counter and closes the connection. ...
10
votes
1answer
258 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 ...
7
votes
3answers
6k 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 ...
7
votes
3answers
7k views

Recommended switch for an iSCSI implementation [closed]

We want to implement an iSCSI SAN and all of our testing has shown that we can implement this quite cheaply (Starwind target, refurbished HP Storage array). What concerns me is the throughput/latency ...
19
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2answers
6k views

What is the command to flash a NIC link light?

I remember using a command line tool to flash a NIC's link light to identify it. I can't remember for the life of me what it was.
17
votes
2answers
8k 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 ...
17
votes
2answers
879 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 ...
14
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6answers
15k views

How do you avoid network conflict with VPN internal networks?

While there's a wide variety of private non-routable networks across 192.168/16 or even 10/8, sometimes in being thoughtful of potential conflict, it still occurs. For example, I set up an ...
13
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4answers
42k 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 ...
9
votes
1answer
19k views

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 ...
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 ...
7
votes
7answers
16k 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 ...
6
votes
4answers
7k views

Should a webserver in the DMZ be allowed to access MSSQL in the LAN?

This should be a very basic question and I tried to research it and couldn't find a solid answer. Say you have a web server in the DMZ and a MSSQL server in the LAN. IMO, and what I've always ...
5
votes
2answers
6k views

Unable to Share Data between Amazon EC2 Instances for Windows

I have two Amazon EC2 Instances running Windows Server 2003 and IIS 6.0. Both the instances are created in the same region and have the same Security Group. I enables icmp for all ports and connection ...
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 ...
3
votes
2answers
5k 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 ...
37
votes
8answers
258k 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 ...
12
votes
5answers
28k views

How can I list my open ports on Debian?

What is the command to display a list of open ports on a Debian server? I tried netstat -a | egrep 'Proto|LISTEN' but I would like something more specific that actually lists the port number.
11
votes
11answers
65k views

How do I find out which devices are on a network?

How do I scan a network to find out which devices are on it? (I'd be happy with a list of MAC addresses and IPs.) For example, lets say I'm at work and want to be sure that there are no unknown ...
9
votes
3answers
742 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 ...
7
votes
3answers
1k 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
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3answers
6k 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 ...
6
votes
1answer
3k 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 ...
5
votes
5answers
6k 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 ...
4
votes
2answers
8k views

What is the correct network configuration for a devStack VM (virtualbox)?

Usually when I setup a new Ubuntu VM, i keep the eth0 in NAT mode to get the internet & I add a eth1 interface in HostOnly mode so that I can ssh. But using this devStack guide : Running a Cloud ...
3
votes
1answer
7k 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

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 ...
3
votes
1answer
5k views

Keepalived for more than 20 virtual addresses

I have set up keepalived on two Debian machines for high availability, but I've run into the maximum number of virtual IP's I can assign to my vrrp_instance. How would I go about configuring and ...
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 ...
2
votes
2answers
4k 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 ...
0
votes
3answers
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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 ...
23
votes
5answers
3k 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 ...
17
votes
4answers
12k 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 ...
16
votes
3answers
2k 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 ...
11
votes
3answers
19k 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
votes
4answers
10k 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 ...
10
votes
3answers
2k views

How are IP addresses actually assigned?

I'm having a hard time understanding how a governing body assigns IP addresses, companies use BGP to advertise those IPs, and how the internet works. Then, where the hell does DNS come in? Can ...
10
votes
4answers
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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
2answers
11k 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 ...
10
votes
5answers
25k 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 ...
9
votes
10answers
7k 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
5answers
12k 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 ...
7
votes
4answers
880 views

CIDR Ranges for Everything except RFC1918

I'm looking for a list of CIDR blocks for "The Internet", i.e. everything from 0.0.0.0 to 223.255.255.255, excluding RFC1918 address space of 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 (yes, I know ...
7
votes
5answers
80k views

Cannot enable network discovery on Windows Server 2008 R2

I'm trying to enable the Network Discovery feature on a newly installed Windows Server 2008 R2 instance. The network connection is in the Home or Work profile (it is not domain joined). These are the ...
7
votes
6answers
7k views

How do I view the TCP Send and Receive Queue sizes on Windows?

Linux netstat shows send and receive queue sizes. How do I get this info under Windows, specifically Server 2003?
5
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2answers
2k views

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
votes
3answers
5k views

Kernel Log “TCP: Treason uncloaked!”

On one linux server (Gentoo hardened), we are experiencing bursts of the following messages in dmesg from time to time: TCP: Treason uncloaked! Peer xx.xx.xxx.xxx:65039/80 shrinks window ...
5
votes
2answers
4k 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 ...
5
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 ...