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

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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 ...
3
votes
2answers
1k 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 ...
2
votes
1answer
12k 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 ...
0
votes
2answers
744 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?
75
votes
17answers
38k 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 ...
54
votes
2answers
327k 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?
31
votes
3answers
23k 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 ...
22
votes
4answers
12k 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 ...
10
votes
4answers
27k 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 ...
41
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.
30
votes
8answers
11k views

When/why to start subnetting a network?

Under what conditions does one start to consider subnetting a network? I'm looking for a few general rules of thumb, or triggers based on measurable metrics that make subnetting something that should ...
16
votes
3answers
20k 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 ...
33
votes
6answers
207k 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?
30
votes
9answers
33k 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 ...
42
votes
4answers
20k 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 ...
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 ...
10
votes
3answers
26k views

Bridging wlan0 to eth0

On arch Linux, I would like to mainly have eth0 (connected to bridged router) share the connection recieved from wlan0, Ive read tutorials but I'm not command sabby as other users are and don't ...
23
votes
8answers
30k 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 ...
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 ...
15
votes
7answers
21k 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 ...
14
votes
5answers
78k views

How to route different traffic thru different network interfaces (in Windows)

I've searched for details on how to do this but I've been unsuccessful - I wondered if someone could offer up some advice. So, let's say I have 2 network cards (LAN and 3G in my instance), both ...
9
votes
8answers
16k 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 ...
14
votes
1answer
674 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 ...
14
votes
7answers
25k 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 ...
3
votes
2answers
6k 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 ...
17
votes
3answers
1k 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
6k 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 ...
11
votes
2answers
2k 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, ...
4
votes
6answers
2k 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 ...
18
votes
9answers
14k 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 ...
11
votes
7answers
478 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 ...
8
votes
4answers
8k 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 ...
8
votes
1answer
13k 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 ...
8
votes
3answers
27k views

How do I force specific permissions for new files/folders on Linux file server?

I'm having an issue with my install of Ubuntu 9.10 (file server) and its samba permissions. Logging in and reading works fine. However, creation of new directories by users restricts access for other ...
4
votes
2answers
6k views

Should I rate-limit packets with iptables?

I'm using iptables on Ubuntu Server. It's a web server on a VPS. I'd like to know if I should rate-limit packets. If so, what should I rate-limit? And should I do so globally or per IP address? ...
23
votes
4answers
1k views

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 ...
14
votes
3answers
43k 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 ...
13
votes
4answers
8k views

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 ...
13
votes
7answers
7k 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
4answers
24k views

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 ...
11
votes
3answers
26k 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
5answers
29k 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 ...
5
votes
2answers
3k 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 ...
5
votes
3answers
8k views

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 ...
5
votes
5answers
7k 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 ...
5
votes
5answers
16k views

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 ...
4
votes
3answers
14k views

Ethernet frames: what are the source and destination MAC addresses?

Imagine you have some network configured like this +-----+ +------+ +------+ +-----+ |comp.|---|bridge|---|router|---|comp.| | A |---| B |---| C |---| D | +-----+ +------+ ^ ...
2
votes
1answer
5k views

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; }
2
votes
2answers
7k views

how to forward wlan0 to eth0?

I get internet from my wireless wlan0 and I would like to forward it to eth0 which is connected to another laptop. How can I do that? Thanks. Edit: my wireless card is intel: 0b:00.0 Network ...
13
votes
2answers
22k views

How do I clear the interface stats on Linux

So one of my clients configured one of their switches and the resulting configuration resulted in a duplex mismatch between the switch and a Linux host. We have fixed the duplex mismatch, but is ...