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Questions tagged [subnet]

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.

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.

Subnetting provides a way to use the number of IPv4 addresses in an optimal way. The previous notation with classes caused a lot of IP's to remain. In the beginning this was not a problem, but these days IPv4 addresses have already depleted at the top level.

Source: wikipedia

Tutorial on subnetting

908 questions
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8 answers

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 by hand or in your head? Can someone explain both conceptually…
Kyle Brandt
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5 answers

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 network I need to know how much of this knowledge is transferable and…
Michael Hampton
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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?
Alan H
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52
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6 answers

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?
Bob
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48
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Connecting to a remote server through a VPN when the local network subnet address conflicts with a remote network

This is a Canonical Question about solving IPv4 subnet conflicts between a VPN client's local network and one across the VPN link from it. After connecting to a remote location via OpenVPN, clients try to access a server on a network that exists…
John Russell
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48
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5 answers

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?
Kyle Brandt
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43
votes
3 answers

IPv6 subnetting a /64 - what will break, and how to work around it?

In IPv6, you are not supposed to subnet to anything smaller than a /64 (RFC 5375). Among other things, SLAAC does not work with smaller subnets, and apparently also some other features will break. What are the workarounds for situations where ISPs…
Kevin Keane
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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 and 255.0.0.0 respectively.
pro
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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 be considered.
Adam Davis
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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 have not been able to figure out how to specify a…
harrije
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What is the network address (x.x.x.0) used for?

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 the same practice: $ ipcalc -n -b…
Shtééf
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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?
Amandasaurus
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What is the difference between 0.0.0.0/0 and 0.0.0.0/1?

In the history, I mostly used 0.0.0.0/0 for "match every IP address". Recently, I saw a 0.0.0.0/1 subnet filter. What is the difference between 0.0.0.0/0 and 0.0.0.0/1 and what's the practical use of 0.0.0.0/1?
Arakis
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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 the Linux server netmasks from 255.255.255.0 to…
ewwhite
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5 answers

multiple physical interfaces with IPs on the same subnet

I have a linux box with 9 NICs on it, and I want eight of them to have unique addresses on the same subnet, e.g.: ifconfig eth1 192.168.123.1 netmask 255.255.0.0 ifconfig eth2 192.168.123.2 netmask 255.255.0.0 ifconfig eth3 192.168.123.3 netmask…
frustrated_tester
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