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41 votes
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What is the difference between 0.0.0.0/0 and 0.0.0.0/1?

The 0.0.0.0/0 matches every IP address, whereas 0.0.0.0/1 only matches half of them (0.0.0.0-127.255.255.255) and requires 128.0.0.0/1 as its pair to match the rest (128.0.0.0-255.255.255.255). In ...
Esa Jokinen's user avatar
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30 votes

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

If you need a temporary dirty workaround to a single or a handful known server ips, the simplest solution should be the static client side routing option. In my case I added my desired destination ...
Aydin K.'s user avatar
  • 401
29 votes
Accepted

Does a Gateway of a Subnet need to be a "real" Computer?

Default route (aka gateway address) has to be owned by something that is capable of forwarding packets to the rest of the internet, and which is willing to do so. It doesn't have to be the "principal"...
MadHatter's user avatar
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20 votes
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How can we explain CIDR notation with /24 and /32 to a manager?

An ip address consists of four numbers separated with a dot between each. You read it from left to right, and each dot adds a level of detail. This is very similar to a real address, think about: ...
Ron Trunk's user avatar
  • 2,179
19 votes
Accepted

AWS: NAT Gateway in public subnet. Why?

A NAT Gateway (as well as a NAT Instance, for what it's worth) must be in a public subnet because only devices on public subnets can actually use a public IP address. That's what makes a public ...
Michael - sqlbot's user avatar
15 votes
Accepted

Blocking or rate-limiting IPv6: what size prefix

The best algorithm is to start blocking separate addresses. Then when multiple addresses are blocked in the same /64 you block the whole /64. Repeat that for bigger aggregates. Prefixes are usually ...
Sander Steffann's user avatar
15 votes

Does a Gateway of a Subnet need to be a "real" Computer?

The IP address of the gateway can be any valid host IP address in the subnet, i.e. not the network address itself nor the broadcast address. This IP address does not need to belong to a single ...
Tommiie's user avatar
  • 5,685
14 votes

How to pick AWS CIDR within the CIDR ranges of VPC?

The best start is to refer to VPC and Subnet Basics which explains the VPC addressing and sizing reqirements. Not sure if you are familiar with CIDR addressing? Essentially the bigger the number after ...
MLu's user avatar
  • 25.6k
13 votes

Export my whole AWS architecture into file?

You can use CloudFormer to export your existing AWS infrastructure into CloudFormation template. Alternatively you can use terraforming ruby gem to export your infrastructure as Terraform files.
AlexD's user avatar
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11 votes
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I am able to ping a device on a different subnet without passing through a L3 device. How?

Route Print on my local machine shows: 192.168.10.99 255.255.255.255 On-link 10.168.10.154 26 That is why, the On-link routes are accessible locally without any gateway, many times they are ...
arana's user avatar
  • 253
10 votes

How does IPv4 Subnetting Work?

I’ll pose and answer a few related questions along the way: Why do you see 255.255.255.0 so often? Why 192.168.0.1? Why 127.0.0.1? Why such weird numbers — 255, 192, 168, 127? 8+8+8+8-bit dotted ...
10 votes

Linux : Ping all the host in the subnet

You can always try to ping to the broadcast address of your subnet. It depends on your local network setup, but you can find it out with $ ifconfig wlp4s0 | grep Bcast inet addr:192.168.199.47 ...
Nils Magnus's user avatar
10 votes

What is the difference between 0.0.0.0/0 and 0.0.0.0/1?

What is the difference between 0.0.0.0/0 and 0.0.0.0/1 0.0.0.0/0 matches all IPv4 addresses. 0.0.0.0/1 matches the IP range from 0.0.0.0 to 127.255.255.255 IP routing uses a "longest prefix ...
Peter Green's user avatar
  • 4,366
9 votes

Does a Gateway of a Subnet need to be a "real" Computer?

"Logical entity" in your usage is a tiny bit confusing. But I'll try to answer it best I can. From my experience, a gateway in an IP configuration is usually a physical device. While it doesn't have ...
kelvintechie's user avatar
8 votes
Accepted

What's the difference between a subnet and a netblock?

I'm not sure that there is an official definition of "netblock", but in common usage, I've most frequently heard it used in reference to an IP address allocation assigned by an RIR to another ...
EEAA's user avatar
  • 110k
8 votes
Accepted

Ping works but TCP doesn't in a bit of an unusual topology

Your network is working as expected. Lets draw it: This is a simplification I'm sure, but has enough information here to show the problem and the various fixes (and their drawbacks) Assumptions ...
Criggie's user avatar
  • 2,310
8 votes

How does VLAN subnetting work on IPv6?

VLANs are layer 2 constructs, not layer 3. You pass frames inside a VLAN regardless of layer 3 protocol by switching. For crossing VLAN boundaries, a router is required. Just like with IPv4, if you ...
Zac67's user avatar
  • 12.2k
8 votes

How can we explain CIDR notation with /24 and /32 to a manager?

You don't need even that detail. Simply treat them as magic values: Short answer: An IP address has four blocks of digits. There is a standard notation called CIDR where if you put /24 at the end it ...
Ángel's user avatar
  • 912
7 votes

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

The Answer from Aydin K. is for linux. If your want the same funtionality for windows, you can type route ADD 192.168.1.10 <IP of tunnel adapter> or route ADD 192.168.1.10 IF <interface ...
OllowainT's user avatar
7 votes
Accepted

Allow internet access for ec2 instances with private IP addresses inside a public subnet?

You are misunderstanding / misusing Public and Private subnets. A public subnet has an Internet gateway (IGW). Instances in the public subnet need public IP addresses to access the Internet. A ...
John Hanley's user avatar
  • 4,974
7 votes

What does the netmask in an IP address actually tell you?

how does the netmask let us distinguish two IP addresses? It doesn't. I lets us or a device distinguish the scope of the network to which it is attached. I don't see how these are two different ...
YLearn's user avatar
  • 1,247
7 votes

Subnet mask for 192.168.1.7/30

With 192.168.1.7 255.255.255.252, the addresses range from 192.168.1.4 - 192.168.1.7. 192.168.1.4 is the network address. 192.168.1.7 is the broadcast address. You cannot apply either of those 2 ...
Bib's user avatar
  • 221
6 votes

What does the netmask in an IP address actually tell you?

The network mask is not part of the address. It defines how big your neighborhood is, as in Mikhail Khirgiy's example. With a /8 mask, Bob knows everyone in New York personally. He can hand-deliver ...
Charles Burge's user avatar
6 votes
Accepted

NAT gateway for ec2 instances

Generally you will have 2 kinds of subnets in a VPC: Public subnet has IGW and optionally NAT 0.0.0.0/0 there points to the IGW hosts (EC2 instances) must have public IP or elastic IP attached as ...
MLu's user avatar
  • 25.6k
6 votes
Accepted

How to route only specific subnet to OpenVPN Server

Remove the: redirect-gateway def1 From your client configuration.
SYN's user avatar
  • 1,794
6 votes

How can we explain CIDR notation with /24 and /32 to a manager?

... how many house numbers the street has. If you have more than 256 houses in a street, you need to use part of the street number for house numbers. This is only important to know when you want to ...
Simon Richter's user avatar
6 votes
Accepted

What does the subnet mask of the tunnel ip in Wireguard do?

The subnet mask does nothing WireGuard-specific. WireGuard itself does not use or care about the subnet masks on its interface addresses (or even use or care about the addresses themselves). However, ...
Justin Ludwig's user avatar
6 votes

Can a gateway use the network address, or can the network address be anything other than the first number in that subnet range?

You are correct and this is wrong. An IP(v4) address ending in .8 in a /29 subnet has all host bits set to 0; thus it's the network address and it can't pinpoint any specific host. It's just as ...
Massimo's user avatar
  • 71.5k
5 votes
Accepted

Why does this allocation of client static IP in OpenVPN fail?

This problem is created because openvpn is trying to parse your ifconfig options as an ip followed by an subnet mask. According to the man page: --topology mode ... subnet -- Use a subnet rather than ...
Ferrybig's user avatar
  • 189
5 votes
Accepted

What significance does the subnet mask have for a public IP address?

The difference is that your ISP has an assigned IP range of 254 addresses (or maybe more than one but this is the subnet you are in). Every ISP has that. This differenciates his subnet from those of ...
Broco's user avatar
  • 2,029

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