Questions tagged [subnet]

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

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How to aggregate a routing table given IP addresses and their subnet masks

Novice networker here. I can't seem to find any straightforward answers online. Example: IP SUBNET NEXT HOP > 129.10.112.0 255.255.255.0 R1 > 129.10.80.0 255....
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2answers
859 views

Does IPv6 have similar concept of network mask?

Does IPv6 have similar concept of network mask? How does it represent a network? In the output of ifconfig, does prefixlen 128 represent a network mask? lo: flags=73<UP,LOOPBACK,RUNNING> mtu ...
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4answers
24k views

Multiple sub-nets behind a router

I have 3 simple questions:- Is is possible to have multiple subnets behind a router? I believe it is, e.g. router LAN interface would have subnet mask 255.255.0.0 and machines connecting to the ...
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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 ...
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2answers
208 views

Carrying remote VLAN via 2 routers to the local gateway

I have a serverA (192.168.15.1) from site A and VLAN is 15, however the VLAN 15 gateway is set at site B (192.168.15.254). There are two ISP routers as a metro role to connect each other by subnet ...
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1answer
820 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 ...
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6answers
51k views

Communication between different subnet MASKS with IP address that works for either

This may be a dumb question. Actually I'm sure of it, but i'd like a thorough explanation for it so i can wrap my head around it consider a switch with two (or more) connected devices, with similar ...
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3answers
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When is /31 recommended over /30 in P2P links? [duplicate]

For your average enterprise network, what are the pros and cons for using a /31 mask on point-to-point links with private addressing over the generally accepted practice of using /30? There's really ...
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2answers
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How does the ARP table work in case of the Gateway Router?

Suppose I am a host, I understand how ARP works in case I address an IP within my subnet. For each IP address there is a corresponding MAC address, and the owner responds to my broadcast ARP query. ...
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5answers
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Different subnets in the same LAN

I have a very rudimentary doubt. We know that a LAN has addresses in the same subnet. The LAN ends at the gateway router with that interface also belonging to the same subnet. But what exactly will ...
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1answer
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Multiple VLANs with same subnet behind single ASA

Suppose you have three groups of servers on the following VLANs and subnets: Name VLAN ID Subnet ----------------------------------- Production 3 10.0.0.0/24 Test 103 ...
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1answer
732 views

Pinging across different subnets? This shouldn't work but it does

I have two computers: PC1 and PC2. PC1 has an IP address of 10.0.0.1/30, and PC2 has an IP address of 10.0.0.6/30. They are connected directly to each other with a crossover cable. My understanding is ...
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4answers
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Multiple IP Addresses on VLAN Interface (SVI)

Let's say that there is a SVI for VLAN 100 and it's been assigned the first usable IP address in subnet 192.168.1.0/24. There is a host on VLAN 100 with an IP address of 192.168.1.130. We need to ...
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3answers
2k views

VLANs and Subnets Smaller than /24?

I would like to get some advice on this, because I see it being mentioned repeatedly, but why are VLAN subnets recommended to be /24? What are the downsides to assigning VLAN's a subnet that are ...
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3answers
7k views

How will be the ARP Request (Unicast/Broadcast) if Subnet Mask is Unknown

Please help me with one doubt regarding ARP requests. Based on my understanding the subnet of an IP is identified by it's Subnet Mask so consider this scenario:- Suppose Device1 with IP- 30.129.33....
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3answers
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Why can't devices in different subnets talk with each other?

I know that the layer 2 doesn't understand IP, and the broadcast domain is same. Why can't devices talk, how does it happen?
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2answers
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Why are IPv6 addresses so long?

By convention, each device on the LAN under IPv6 gets a /64 subnet, right? That's an obscene number of addresses per device! Why not make the addresses shorter, say, 72 bits, then each device would ...
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2answers
1k views

Can a single subnet work across several switches?

New to networking and studying hard but limited access to a kit to try things at the moment... My question is - if I had, for example, two Layer-2 switches cable connected, could I have devices on ...
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4answers
1k views

Are private IP addresses the outcome of subnetting a public IP address?

I understand the purpose of both but just verifying if this correlates together at all.
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832 views

Can a large broadcast domain break accesspoints

I have a network with a large class B broadcast domain (172.16.0.0/18 - 172.16.192.0/18) with a single DHCP server. I have lots of L2 switches in this network but there is no VLAN configured. My ...
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1answer
557 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 ...
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2answers
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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 ...
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1answer
856 views

CIDR notation and subnets

I've been given a script that will create a virtual network with the following IP range (in Azure): 10.0.0.0/16. The script then goes on to create two subnets within that network with the following ...
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4answers
314 views

Subnetting Issue with legacy network and poor planning

A client of mine is part of a bigger group of companies running a MPLS for connectivity. My Clients IP Address range is 192.168.13.0/24. We use this with DHCP and MASK of 255.255.255.0 and our ...
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2answers
619 views

Is the first address in an IPv6 subnet assignable?

I am working in a lab and have configured a series of /125 subnets between routers. Lets ignore the best practice for this discussion of using /64 for everything. When I assign fd00:f9a8:ffff::257 to ...
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1answer
679 views

Same Vlan Name / ID on different switches network subnet same or different?

I have several switches (some on same floor and another on other floors) all connected to core layer 3 switches through trunk links. One of the vlan id / name is repeated along the switches. May I ...
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2answers
119 views

Whether we usual use dot-decimal notation to represent network or IP by opposite mask?

Whether we usual use dot-decimal notation to represent network or IP by opposite mask? 10.10.10.0 0.0.0.255 # a network 10.10.10.0 255.255.255.0 # a IP Update if we represent a network, we can use ...
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1answer
2k views

What is the purpose of EIGRP stubs?

I have a strong background in OSPF and am now learning EIGRP so everything I read gets compared to my existing knowledge of OSPF. Because of this, I don't see the purpose of EIGRP stubs. In OSPF, you ...
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4answers
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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 ...
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3answers
10k views

Can I set two gateways or more on the same subnet with NAT on a Cisco router?

Let's say I have the the following configuration on a Cisco router. ISP 1 Connected and configured into GigabitEthernet8. VLAN 1 192.168.0.0/24, NAT configured. Gateway is 192.168.0.1. ISP 2 ...
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3answers
8k views

Why are number of hosts on a subnet less than the number of combinations we can make with the bits remaining?

Suppose we have a Class C Subnet (255.255.255.0), why do we get to have 254 hosts on it even though we have 256 unique internal IPv4 addresses from 192.168.1.0 to 192.168.1.255? Even if we scale up ...
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3answers
712 views

Connection between 2 end devices with different subnet masks (Packet Tracer)

I was just wondering why Packet Tracer allows 2 end devices to ping each other even though they're specced with 2 different subnet masks? am i missing something here? i.e. PC1: 192.168.1.10/24 PC2: ...
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2answers
4k views

Using a public IP for select hosts in a LAN

I have a small company and we just started out. Given our size, we really can't get a dedicated network guy for now. Recently, we moved to a lease line of our own for reliability. This is the ...
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1answer
928 views

Multiple VLANs under one subnet (for traffic control)

Looking at a fiber ring network of 11 switches on the same subnet, with 3 types of devices per module (device 1, 2 & 3). control room switch 192.168.11.100 module 1 ethernet switch 192....
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1answer
3k views

New Ubiquiti EdgeRouter and UniFi AP - keeping networks separate but reachable

I've got a Ubiquiti EdgeRouter PoE (5 port) which I'm setting up just now. I'm trying to achieve a solution where the single UniFi AP can hand out IP addresses in the 10.0.2.0/23 space, while devices ...
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2answers
1k views

Why have a single, "core", router

quick bit of context so my question makes sense: I've been asked to plan out some subnets and routing for a new IP range we've just been allocated. The range will be used to customer's equipment (on ...
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1answer
2k views

Multiple VLANS or single large subnet for WiFi with potential 1500+ users

I have an outdoor venue where I'm planning a wifi network, the venue covers 350 meters by 350 meters. This is not a question about equipment but only about the planning in theory. I will deploy ...
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2answers
16k views

VLANs and IP addressing

I have been tasked with setting up some VLANs on 10 HP 2520 switches. This is a departure from my normal IT support area so thought I'd seek out a little advice from more knowledgable people. These ...
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1answer
292 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 ...
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2answers
411 views

BGP vs OSPF path selection with /24 vs /23`

would a network select /24 or /23 path with ospf or with BGP which one is preferred !!
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3answers
17k views

Calculate subnet mask from IP Address

I have an IP address 12.23.34.22 I need to find the network prefix for this IP Address. For that I need to find the subnet mask and then count the number of contiguous 1s to get the network prefix. ...
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3answers
1k views

Do VLANs within a subnet need to have their own subnet for router on a stick?

I have been creating a network lab in packet tracer for practice. I have 3 vlans in subnet A and I am trying to configure router on a stick at gig6/0 on the bottom left of the image. Do I need to ...
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2answers
821 views

What determines the private ip addresses? [closed]

Right now, I am using internet at home, and my private ip address is 192.168.x.x. At work my private ip address is 10.x.x.x. In both of the scenarios, I did not play any role in selecting my ip, I ...
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2answers
3k views

subnetting, nested subnetting, VLSM & broadcast addresses

A teacher told us about VLSM and "nested subnetting": you should NOT use all-1 / all-0 subnets the same public network you got, can be split up in subnetworks of different size / having different ...
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2answers
654 views

Why I Can't Summarize (aggregate) These Subnets in BGP router?

In a BGP routing context, giving these networks address: 192.168.0.0 /28 192.168.0.32 /28 For me, the summary address will be : 192.168.0.0 /26 But someone tells me that this is impossible because ...
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3answers
4k views

Can 2 seperate lans share an unmanaged switch

Can i have two process networks using the same unmanaged switch?
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4answers
260 views

Carving out a /28 network and still maintaining access to parent /24 network

In the diagram below, I'd like to carve out a /28 network from 192.168.0.0/24 and move it to another geographical location and still maintain access in and out of the original /24 network. ...
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3answers
917 views

A VLAN maps several subnet

I've read the post Multiple Subnets in a VLAN and am wondering about the possible conflicts when using several subnets in a VLAN. The recommended design is of course put a IP subnet in a VLAN. If I ...
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2answers
176 views

Can I always separate two IP addressess into two subnetworks?

I was reading How do you calculate the prefix, network, subnet, and host numbers?, and I noticed that he divided the network space into 4 subnetworks of 256 addresses, but he needed only 100 per ...
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4answers
1k views

Network Address used for hosts?

I was always taught that a network address (eg. 192.168.1.0) cannot be the IP address of a host? Is there a reason for this? After all it isn't used anywhere else like a broadcast address.

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