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77 votes
Accepted

Why can't I use the first or last address in a subnet?

In a /24 network you can't use 0 because it is the identification of the network (devices use it to recognize the different networks they are connected to). In a Windows PC open a Command Prompt and ...
jcbermu's user avatar
  • 17.6k
62 votes
Accepted

How can every single device on a network have a different public IP?

They own an IP range, and are using the range to directly connect to WAN (Internet) instead of hiding behind NAT (Network Address Translation). Basically, NAT was made for environments lacking enough ...
NetwOrchestration's user avatar
62 votes

What does it mean to have a subnet mask /32?

/32 addressing Generally speaking, /32 means that the network has only a single IPv4 address and all traffic will go directly between the device with that IPv4 address and the default gateway. The ...
Worthwelle's user avatar
  • 4,718
54 votes
Accepted

Why can I ping 10.0.0.0/8 addresses from a 192.168.1.0/24 subnet?

I thought 10.0.0.0/8 were all reserved addresses and that any sort of traffic going to those addresses was dropped. No. It's true that it's a special range, but it's reserved for exactly the same ...
grawity_u1686's user avatar
44 votes
Accepted

Is a class C private IP address range (or even class A or B) both theoretical and practical or is it just theoretical?

To start with, classful addressing has not been used since the mid-90s. Everything uses CIDR now, which allows splitting an IPv4 address space into any size from a /32 (2^(32-32) = 1 address) to /0 (2^...
Bob's user avatar
  • 62k
39 votes
Accepted

What does it mean to have a subnet mask /32?

There's a bit of confusion here; that /32 doesn't refer to the size of any (sub)network, but to the range of addresses that particular routing table entry applies to. Usually the two are the same (...
Gordon Davisson's user avatar
21 votes

Why can I ping 10.0.0.0/8 addresses from a 192.168.1.0/24 subnet?

These are three most likely possibilities: Your ISP assigns its clients the 10.0.0.0/8 addresses. Your home router isn't advanced enough (nor needs to be) to limit routing private blocks upwards. You ...
Michał Sacharewicz's user avatar
20 votes

Is it OK to use mixed DNS servers (e.g., Google as primary and Quad9 as alternate)?

It won't do what you think it does. If the primary server returns an empty response (no IP addresses match a domain name), the alternate server will not be queried at all. On most platforms the ...
gronostaj's user avatar
  • 57.5k
19 votes

How can every single device on a network have a different public IP?

Back in the old days (before the Public Internet came into being in 1991), technologies like NAT were not common, and most operators did not use RFC1918 addresses. They didn't divide the Internet into ...
Frank Thomas's user avatar
  • 36.4k
18 votes

How can every single device on a network have a different public IP?

This is how the internet is supposed to work. People started using private address ranges and NAT because the number of spare IP addresses started to get used up. And then people found that using NAT ...
John Burton's user avatar
16 votes
Accepted

What is IPv4 Autoconfiguration and why it overwrites static IP

The screenshot shows an IPv4 address that start with 169.254. This is from the "link local" range (e.g., RFC 3927 page 31 discusses what Windows XP using these addresses). Some people call ...
TOOGAM's user avatar
  • 16k
16 votes

Is a class C private IP address range (or even class A or B) both theoretical and practical or is it just theoretical?

They are real/concrete limits, not just theoretical. There's nothing about IP addressing schemes that "pushes the boundaries" of the technology, so it works exactly as advertised. A Class-C uses 8 ...
Frank Thomas's user avatar
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15 votes
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How web browser determines when to use IPv4 or IPv6 to connect to the destination?

First: How you resolve a hostname has nothing to do with what address you can resolve it to. DNS servers are perfectly capable of returning IPv6 AAAA records when asked via IPv4, and vice versa. As ...
grawity_u1686's user avatar
14 votes
Accepted

Accidentally changed an IPv4 setting on Synology NAS Cannot access it anymore

Synology NASes have a networking reset procedure: Locate the RESET button on your Synology NAS. Use a paper clip to gently press and hold down the RESET button for about 4 seconds until you hear a ...
gronostaj's user avatar
  • 57.5k
13 votes
Accepted

What does (Preferred), (Tentative) and (Duplicate) mean against an IPv4 Address with ipconfig

Preferred is what your client will ask the DHCP server for when it gets/renews the lease, but tentative is what it got in the response. Someone else probably has a lease on the preferred address. ...
Peter's user avatar
  • 594
10 votes

Why can't I use the first or last address in a subnet?

Note that you can not use the first and last address in the range if it is used to number devices in a broadcast domain (i.e. a physical network or a vlan etc.). As the other answer indicates indeed ...
hertitu's user avatar
  • 306
9 votes

Is it OK to use mixed DNS servers (e.g., Google as primary and Quad9 as alternate)?

You can view both adresses as totally separate. The DNS is just a big "phonebook" of IP adresses. It doesn't matter where and from which provider your system gets them from, as long as that ...
Caeleste's user avatar
  • 841
8 votes

What is IPv4 Autoconfiguration and why it overwrites static IP

As the alternative to editing registry you can try this solution: open command line check id of network connection - it will be in the 1st column: netsh interface ipv4 show inter run this command ...
jacob_w's user avatar
  • 91
8 votes

What does it mean to have a subnet mask /32?

It is just CIDR value. You can learn more in here for CIDR. TL;DR A CIDR network address looks like this under IPv4: 192.30.250.00/18 The "192.30.250.0" is the network address itself and ...
recanavar's user avatar
7 votes

Why can't I use the first or last address in a subnet?

A reading of Internet Standard Subnetting Procedure, Toward an Internet Standard Scheme for Subnetting and specifically BROADCASTING INTERNET DATAGRAMS IN THE PRESENCE OF SUBNETS section 7 describes ...
Pekka's user avatar
  • 171
7 votes
Accepted

MacOS route table incomplete IP addresses and masks

The version of netstat that macOS (and maybe other BSD-derived unixes?) comes with uses a somewhat idiosyncratic shorthand for the address and netmask. As you inferred, it uses CIDR notation in the ...
Gordon Davisson's user avatar
7 votes
Accepted

/etc/network/interfaces file not found

The file /etc/network/interfaces is not an universal standard. Almost every Linux distribution has its own tool for configuring networks – this file is used specifically by the 'ifupdown' tools from ...
grawity_u1686's user avatar
7 votes

Accidentally changed an IPv4 setting on Synology NAS Cannot access it anymore

Okay, if your Synology still has its default IPv6 setup you can try to find it via the IPv6 Neighbor Discovery Protocol. The NDP list shows only devices, which had communicated to each other. So we ...
megamorf's user avatar
  • 2,404
7 votes
Accepted

Why does peer-discovery work for IPv6 but not IPv4?

And the peer-discovery functionality that I've built works by simply sharing the IP address of connected nodes along with their announced port for incoming connections. There are a few issues with ...
grawity_u1686's user avatar
6 votes

How does IPv4 subnetting work?

IP subnets exist to allow routers to choose appropriate destinations for packets. You can use IP subnets to break up larger networks for logical reasons (firewalling, etc), or physical need (smaller ...
6 votes
Accepted

I can access my website using my IPv4 address but not my IPv6 address. Why?

The reason your external IPv6 IP (the one that looks something like like XXXX:XXXX:XXXX::) doesn't work is because of the way IPv6 works. Take this address for example: 2607:5600:52c:1::. This ...
td512's user avatar
  • 5,110
6 votes

What does it mean to have a subnet mask /32?

easiest thing is web search and read articles related to subnet mask and subnet mask binary shorthand and CIDR and also check out subnet calculators the /32 is the CIDR (shorthand) and refers to how ...
ron's user avatar
  • 758
6 votes

Is it OK to use mixed DNS servers (e.g., Google as primary and Quad9 as alternate)?

You almost always can use multiple resolver operators. Whether it's a good idea depends on your requirements and priorities. You get a combination of the features offered by both providers. Notably, 9....
Matt Nordhoff's user avatar
5 votes

How to get network ip address via windows command prompt?

I'm just building off of @Ashtray's answer, but for me I needed the actual IP address only, so I'll share that here in case anyone else needs to similarly get just the address: Find the name of the ...
Daryn's user avatar
  • 563

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