A subnetwork, or subnet, is a logically visible subdivision of an IP network. The practice of dividing a single network into two or more networks is called subnetting and the networks created are called subnetworks or subnets.

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How does IPv4 Subnetting Work?

This is a Canonical Question about IPv4 Subnets. Related: How does IPv6 subnetting work and how does it differ from IPv4 subnetting? How does Subnetting Work, and How do you do it ...
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Is X.Y.Z.0 a valid IP address?

Are IP addresses with a 0 in the last octet valid? 10.6.43.0 In my case, I have the the following netmask 255.255.252.0 What about a 0 for the other octets?
41
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3answers
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How does IPv6 subnetting work and how does it differ from IPv4 subnetting?

This is a Canonical Question about IPv6 Subnetting. Related: How does IPv4 Subnetting Work? I know a lot about IPv4 Subnetting, and as I prepare to (deploy|work on) an IPv6 ...
28
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8answers
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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 ...
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CIDR for Dummies

I understand what CIDR is, and what it is used for, but I still can't figure out how to calculate it in my head. Can someone give a "for dummies" type explanation with examples?
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Customer site is out of IP addresses, they want to go from /24 to /12 netmask… Bad idea?

One of my client sites called to ask me to change the subnet masks of the Linux servers I manage there while they re-IP/change the netmask of their network based on a 10.0.0.x scheme. "Can you change ...
18
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What are the implications of having two subnets on the same switch?

Can anyone tell me what some of the implications of having two different subnets on the same switch would be if VLANs are not being used?
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5answers
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Are Cisco admins expected to understand classful networks?

While studying for the CCENT exam, my reference materials have made an alarming number of references to class A/B/C networks. Thankfully they just treat Class A/B/C as shorthand for /8, /16, and /24 ...
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What is the network address (x.x.x.0) used for? [duplicate]

It appears to be common practice to not use the first address in a subnet, that is the IP 192.168.0.0/24, or a more exotic example would be 172.20.20.64/29. The ipcalc tool I frequently use follows ...
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12answers
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Is it better to use the 192.168.x.x or 10.x.x.x address range for a small business network?

For best performance and ease of management, is it better to use 192.168.x.x or 10.x.x.x range of addresses for a small (<50 PCs) business network? This would correspond to a subnet of 255.255.0.0 ...
10
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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 ...
10
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Multiple VLANs, multiple subnets, single DHCP server?

At my job we are prepping to transition from multiple LANs connected over slow VPN connections to a single MAN connected over fiber, and I've got a few questions. First of all, we are planning on ...
9
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3answers
688 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 ...
8
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5answers
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A website hosted on the 1.0.0.0/8 subnet, somewhere on the Internet?

Background I'm attempting to demonstrate, using a real-world example, of why someone would not want to configure their internal network on the 1.0.0.0/8 subnet. Obviously it's because this is not ...
7
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10answers
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Is there such a thing as too many IP addresses?

We've started a small debate in the office, and I've hit the point where I no longer have the technical knowledge to continue. Is there such a thing as having too many IP addresses? I'm not ...
7
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6answers
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Running out of IP addresses

We are running out of IP addresses on our expanding network. The current range is 192.168.1.0/24. Considerations: We use an ISA server as a proxy for all web traffic, this is our current default ...
7
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6answers
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Can I subnet a subnet?

Apologies in advance for the botched terminology. I have read the Server Fault Subnet Wiki but this is more of an ISP question. I currently have a /27 block of public IPs. I use give my router the ...
7
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2answers
3k views

Openvpn for client/server in same subnet

I'm trying to openvpn into an office network (192.168.1.0/24) from a client sitting on a network with the same subnet (also 192.168.1.0/24). It is a linux (ubuntu 9.10) server and windows client. I ...
6
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4answers
834 views

Best Approach for subnetting/VLANing traffic?

Our network is currently setup with no subnets or VLANs. We are looking at going to VoIP so this needs to change before VoIP is installed. I believe that we want to use VLANs to separate Voice and ...
6
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1answer
712 views

If I change a router's subnet mask to one that includes the old one, will the hosts with the old configuration still work?

Currently I have a router that is addressed as 10.2.1.1 on a 10.2.1.0/24 network. All of my hosts have default gateway 10.2.1.1 with mask 255.255.255.0. I want to know: if I change my router to ...
5
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4answers
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Linux Command line tool to work with netmasks / CIDR notation

I'm terrible at working out network subnets in my head. Is there some command line tool for linux (ubuntu packages a plus), that lets me put in 255.255.255.224 and it'll tell me that is a /27?
5
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3answers
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Changing netmask from /24 to /16 on a Windows 2003 domain

I have a Windows 2003 domain using 192.168.0.0/24 with all static addresses (no dhcp). I want to move to 192.168.0.0/16 because we need more addresses. I understand that we need to change netmask ...
5
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4answers
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Maximum Number of Hosts per Network

I recall reading this in some (I think) Cisco documentation years ago, but can't find it or any other reference to this recommendation. Anyone know what I'm talking about? Anyone still follow these ...
5
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1answer
195 views

In what scenarios would a VLAN not align 1:1 with a subnet?

Under what scenarios would a VLAN not align with a subnet. I've been told that genearlly they always go 1 to 1. What are some examples or scenarios, and reasons for anything besides that, and for what ...
5
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6answers
367 views

Performance Benefits of Adding a Second Network

We transfer large media files to and from a few workstations and file servers (audio/video files, as large as 20GB each in some cases) and sometimes I get the feeling the network is bogged down as a ...
5
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4answers
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Networking Question - What is a VALID Subnet Address? [duplicate]

Possible Duplicate: How does IPv4 Subnetting Work? I am currently revising Networking for the Cisco CCNA1. One of the questions that I am struggling to answer is the following: Which of ...
4
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3answers
659 views

Best way to break up a large subnet

I have ran into a 10.10.50.0/20 network that is having issues with packets dropping. They run all unmanaged switches and I imagine the huge amount of devices on one subnet is causing issues. I've ...
4
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5answers
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How to work out how many IP's you've got available on a /29 network mask

This might sound like a stupid question but I would really like to know how I would work out how many IP's I've got available on this network range: 196.44.198.32/29 Can someone explain it to me, ...
4
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5answers
498 views

Share one IP address with a simple router

We have just moved into a new office and have been given our 'internet connection' in the following form: One Ethernet cable in the corner of the room An IP address with subnet mask 255.255.255.0 ...
4
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2answers
255 views

Subnet Mask problem

I'm studying for a test and found myself in a "dead end" with a question about netmasks. The question is: Based on the next figure, once both sub-nets are configured, it's observed that hosts in a ...
4
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2answers
160 views

Is this IPv4 and subnet combination public or private? [duplicate]

Possible Duplicate: How does IPv4 Subnetting Work? I thought I understood this but I am momentarily confused. Here is an example: Are all IPv4 addresses from 192.168.0.0 to 192.168.255.255 ...
4
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5answers
860 views

Tips and Suggestions IP Address Re-Addressing?

My ever evolving and expanding local area network is currently using a class-C address. My network consists of multiple subnets depending on site/location. 192.168.1.x is site HQ 192.168.5.x is ...
4
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5answers
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Two routers on different subnets - will this configuration work?

I'm hoping a network guru can help me out here. I have a network installation project at a client site and I've mentally mapped out how I plan to set it up. They already have a Verizon router set ...
4
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4answers
408 views

Is it reasonable to put all printers to another subnet?

I have a network of about 90 PCs and about 25 network printers. In near future i will promote one server to DC. However, now PCs on my network have static IP addresses. It is a real mess now with ...
4
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1answer
98 views

why would you create two different subnets on the same physical network?

I'm working at a messy location, one of the strange (for me) things is that on the same physical network there are two different subnets. Specifically some computers will have 10.0.0.0/24 and some ...
4
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3answers
4k views

How to configure remote access to multiple subnets behind a SonicWALL NSA 2400

I have a client that uses a SonicWALL NSA 2400 as their firewall. I need to setup a second LAN subnet for a handful of PC. Management has decided that there should be a second subnet even though ...
4
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1answer
246 views

How does broadcasting work on a server with multiple IPs?

Say you have two dhcp servers, A and B. Server A has two IP addresses, 10.0.0.1 and 10.0.0.2. Server B has one IP address, 10.0.0.3. Server A has two instances of isc-dhcp running, one specifying a ...
4
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1answer
3k views

Single m0n0wall - Two LAN Subnets - How To Setup

I have two LAN subnets that I need to link together they are 192.168.4.0/24 and 192.168.5.0/24 There is a m0n0wall running on 192.168.4.1. It's LAN connection goes out to our network switch, and it's ...
3
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3answers
187 views

Why does operating system need to know subnet mask? [duplicate]

If I understand correctly, the operating system gets subnet mask together with IP and other stuff from the DHCP server. And this subnet mask seems to be important for router because it knows if packet ...
3
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4answers
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Can I determine a computer's subnet using ping-type tools?

I know I can ping a server name and determine the IP address. But are there commands I can use to determine the subnet? I'm using Windows XP.
3
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3answers
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Subnetting Challenges

I am trying to plan out a network with the following requirements and am having problems trying to complete a subnet plan for my network. The network consists of 3 routers that connect 3 different ...
3
votes
4answers
824 views

Basic subnetting question

I've been going over my notes for subnetting, and realised I don't really understand it. Have read this fantastic question which cleared up a lot: How does Subnetting Work? However, I'm still stuck. ...
3
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2answers
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How ISPs will assign IPs /subnets for end users in IPv6

Consider two scenarios: The end user has a simple computer, dual-stack The end user has a LAN behind a dual-stack router How will ISPs differentiate each one of these kind of users in IPv6? An ...
3
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3answers
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Building up a network structure

I have the following structure: So in this case I have two different networks. What device can handle this structure, also PoE WiFi. In this case I have two measurement system attached in the PC B ...
3
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1answer
325 views

Subnet Masking in IPv6

I know within IPv4 subnet masking, the network is determined by either the 1st, 2nd or 3rd set of octets. Being there are so many more characters in IPv6, how do you determine the subnet mask?
3
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1answer
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tcpdump filter on network and subnet mask

I'm using the following tcpdump command: tcpdump -w net75.out -s 0 host 65.207.95.222 I want to change the filter on the single host to be all addresses in the following subnet: 65.192.0.0/10 I ...
3
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4answers
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Are network and broadcast IPs supposed to respond?

I have a /24 network that is subnetted into a bunch of small chunks. I have recently gone into each router on the network (mostly Cisco) in order to document how this network had been divided. Now ...
3
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3answers
187 views

What's the formal definition of the magic number of a network? [closed]

I know what the magic number of a network is. I know how to compute it - 2 ^ ((32 - n) % 8). I know what it's used for and how to use it. I don't how how to define it formally. In a recent interview ...
3
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1answer
804 views

Subnetting into 6 CIDR/24 network and 2 CIDR/27 networks?

I am revising some questions for an exam and one of the questions was provide the ip numbers and a diagram for a company which has 3 branches. Paris/Berlin/Cairo (random locations I know) Now I belive ...
3
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2answers
5k views

Bonjour/mDNS Broadcast across subnets

I have just setup a new OSX Server in our office and verified that everything is working fine over our wired network (192.168.126.0/24). The problem that I am having is that our clients (Mac Laptops) ...