Questions tagged [subnet]

Questions relating to IP subnetting, including planning, calculation and best practices.

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123
votes
6answers
759k views

How do you calculate the prefix, network, subnet, and host numbers?

Example: IP: 128.42.5.4 In binary: 10000000 00101010 00000101 00000100 Subnet: 255.255.248.0 How could you determine the prefix, network, subnet, and host numbers?
227
votes
6answers
436k views

The slash after an IP Address - CIDR Notation

What does the "/16" means in here : "192.168.0.0/16", for example.
37
votes
13answers
65k views

Difference between Subnet and VLAN?

You often hear the terms Subnet and VLAN used interchangeably. With the ubiquitous nature of IP these days, when are the two not considered roughly the same from a high-level, understanding that ...
21
votes
8answers
18k views

What is the purpose of network address?

What is the purpose of network address? (aka subnet address, starting address of each subnet) For example in this network: 192.168.1.0/24 Why we should leave 192.168.1.0 address free?
17
votes
4answers
70k views

Confusing A, B, C network classes

I'm studying IPv4 addresses and came across this whole thing about classful addressing. I get the idea behind it, bit there is something I find confusing: There are two "ABC" ranges: First one: A: ...
6
votes
2answers
626 views

VLAN-Subnets 1:1?

I often hear people saying that each VLAN is a subnet (or is associated with a subnet) but is that really true? Assume I have 10 big offices. I will have a subnet for each office but only 2 VLANs ...
19
votes
1answer
7k views

What is the practical use of a /31 CIDR or 255.255.255.254?

With a /31 subnet, we are left with zero usable hosts. The /31 subnet only has two hosts - one for network and another for broadcast. I am wondering why would someone ever use this subnet.
14
votes
4answers
5k views

/31 Point-to-point bitmasks

When is it appropriate to use a /31 network in production, and is using them considered good practice? On a point-to-point link, broadcasts shouldn't be required, so is there any compelling case for ...
6
votes
1answer
1k views

subnetting is incorrect in show ip route output

in one of the CCNA courses theres the following image taken from a routing table: I'm not very confident with my subnetting skills, so please confirm if I'm wrong: 172 is a class B network (/16). So ...
3
votes
1answer
465 views

Finding Subnet Ranges of IPv6

I need to find a single subnet range to cover 10,000 IP addresses (hosts), given the IPv6 Address 2405:1300:c5c1:322::/108 (for example) I am aware of how to do subnet in IPv4 but cannot grasp the ...
1
vote
2answers
343 views

Does the same IP cause IP conflict if one is from /22 other is from /24?

I have two hosts. They both have the same IP/subnet, ex.: 1.2.3.4/24 on both. I know this is bad, since there will be duplicate IP in the network. OK. But: If I have different (?) ranges: 1.2.3.4/...
16
votes
4answers
58k views

Bad Mask for IP Address Error

I'm not too clear on subnetting rules and experienced an error when I tried to assign 148.26.1.176/28 to an interface on my Cisco router. Can someone please explain why it was not allowing me to ...
5
votes
1answer
804 views

IPv6 Link-local addresses

RFC 4291 specifies that IPv6 link-local unicast addresses must have a high-order bit sequence of 1111111010, or fe80::/10. However, the same document specifies that the 54 bits following the first 10 ...
3
votes
1answer
2k views

What is the point of a subnet mask on a local network?

I have a question regarding subnet masks and my understanding (or misunderstanding of them). So when a subnet mask is used, a bitwise AND is performed using the subnet mask and the IP address(es). ...
3
votes
1answer
1k views

Can a 172.168.10.0/28 be a class B Subnet

I am starting my studies in networking and starting off with the basics of IP addressing and Subnetting with CIDR values. My Question here is 1st how can you tell the subnet class of an IP address ...
3
votes
2answers
2k views

Broadcasting traffic by 255.255.255.255 or by “subnet dot all ones”?

If a device wants to broadcast traffic does it send it to the "all ones" IP? (Which is 255.255.255.255)? Or does it send it to "the all ones of the subnet"? (For example if the subnet is 123.123.0.0/...
2
votes
2answers
6k views

Routing Between 2 different vlans but same subnet

I have a basic doubt understanding vlan communication. Scenario: Let's say a single switch and has been configured with 2 vlans (vlan 100 and vlan 200). Vlan 100 connects to lets say 192.168.100.0 ...
1
vote
1answer
170 views

What is the last usable address in an IPv6 network

IPv6 does not have broadcast, so is the last address usable? Besides it being long, is it bad practice to actually use it? For example: A:B:C:D::0/64 starts with A:B:C:D:0000:0000:0000:0000 and ends ...
-1
votes
1answer
126 views

different network mask and subnet mask and netmask [duplicate]

1- what is network mask? 2- what is subnet mask? is there any differnt between network mask and subnet mask? i'm tried to search about network mask and nothing found is it called netmask ? thank you
23
votes
8answers
19k views

Why can't devices on different VLANs, but on the same subnet, communicate?

I have a question about switching. I have two devices connected to a switch with IP addresses 192.168.5.20 and 192.168.5.10. Both devices have the same prefix, /24. That means they are on the same ...
10
votes
4answers
31k views

VRFs, VLANs and subnets: difference

I have a basic understanding of VRFs, VLANs and subnets. I understand that VLANs operate on L2, and subnets and VRFs (lite) on L3. What I don't understand, is why you would choose one over the other ...
9
votes
3answers
6k views

Generate list of subnets on switch using SNMP?

Is anyone familiar with an approach to generate a list of subnets on a particular switch (let's pick a more popular one - Cisco) using SNMP? How about a list of VLANs? If so, can you point me to the ...
15
votes
2answers
3k views

Why are there 3 ranges of private IPv4 addresses?

Why are there three separate ranges of private IPv4 addresses of different sizes? Why not just reserve the largest (10.0.0.0 - 10.255.255.255) range and let people create /16 or /24 (or whatever) ...
6
votes
3answers
2k views

CIDR and VLSM what are the differences?

CIDR improves the allocation of IP addresses. VLSM allows to define a subnet as we wish. Can CIDR used without using VLSM?
8
votes
4answers
5k views

Why do I get “% Warning: use /31 mask on non point-to-point interface cautiously” when I use a /31 subnet mask?

Why do I get % Warning: use /31 mask on non point-to-point interface cautiously when I use a /31 subnet mask over Ethernet, and why am I not able to ping from R1 to R2 when both the interfaces have ...
7
votes
1answer
1k views

Why is an IPv6 Link-Local Address a /10?

I'm currently studying for my CompTIA Network+ Exam and am a bit confused as to why the IPv6 link-local address is a /10 and not a /12 or /16. Since each character in an IPv6 address is 4-bits and ...
7
votes
1answer
54k views

How to divide network into subnets?

I've been trying to figure out how to divide a network number into particular subjects where one of them require a particular number of hosts. I have the Computer Networking: A Top Down Approach but ...
5
votes
2answers
2k views

Can't ping the management IP of Switch

My topology is: I am logged in to R1. I can ping 10.0.0.2 on R2 and 198.51.100.1 on R2, but can't ping the management IP of sw3 (198.51.100.2). What am I doing wrong? R1#sh ip arp Protocol Address ...
4
votes
4answers
5k views

VLANS vs. subnets for network security and segmentation

What are the security implications when using subnets as opposed to VLANs for segmenting an enterprise network? We have strict security requirements surrounding the data we handle and need to ensure ...
4
votes
1answer
287 views

Can computer device with multiple NIC be configured with same subnets for isolated networks? [closed]

Two Networks I have an embedded device using Xilinx ARM processor, with eth0 and eth1. I also have wlan0 and I am running Linux 3.17. PC0 <---left--->[eth0 ARM eth1]<---right:some ...
3
votes
2answers
3k views

Why largest subnets should be assigned IPs first? [duplicate]

Is there any particular reason as of why we should assign IP addresses to the largest subnet first? Could anyone give a simple example of why this is the better option? Let's say I have two subnets: ...
3
votes
1answer
849 views

Multiple Subnets in a VLAN

Is it advisable to have multiple subnets with in a VLAN? If at all ports assigned with differently subnetted addresses are used in a VLAN, will they be able to communicate? Assume the different ...
7
votes
1answer
394 views

Is the first address of the subnet a valid configurable address in case of IPv4 and IPv6 point to point networks?

Am I correct, that first address of the subnet is a valid addresses to configure in hosts/routers in case of IPv4 and IPv6 point to point networks? For example, in case of 192.0.2.0/31 one of the ...
4
votes
2answers
2k views

Some question about the relationship between VLAN , DHCP and subnet

I am new here and very interested in computer networks. From a book, I have some questions, for which I need help. question1: Can there be only one working DHCP server in one VLAN? question2: Can ...
3
votes
4answers
1k views

Should I receive an ARP reply from a host that is logically on a different subnet but is connected to my host via a hub?

Host A: 128.238.66.100/16 Host B: 128.238.67.100/24 The hosts are connected to the same hub and nothing else is connected to that hub. The routing and ARP tables of both hosts are empty. Host A ...
3
votes
3answers
7k views

D-Link L2 & L3 Network Setup

I'm currently setting up my new network using D-Link DGS-1510 series gigabit stackable smart managed switches. It is the first time i use this L2 & L3 switches and I'm trying to setup the ...
0
votes
1answer
51 views

Is it possible to know the mother address of a subnet?

The mother address is X, have Y numbers of subnets (children), we already know 2 of the mother's children, they're: 10.1.192.0 /20 [edited] 10.1.240.0 /20 Is it possible to know the value of X and Y ...
-1
votes
3answers
611 views

how to make multiple subnet able to use one resource without being able to connect to each other in any way

i`m trying to connect multiple subnets to one web server but these subnets should not be able to connect to each other.i cant make any changes on these subnets. I just have a lan cable from each ...