304
votes
Accepted
What's the difference between 127.0.0.1 and 0.0.0.0?
What's the difference between 127.0.0.1 and 0.0.0.0?
127.0.0.1 is the loopback address (also known as localhost).
0.0.0.0 is commonly used as a non-routable meta-address used to designate an invalid,...
- 152k
125
votes
What's the difference between 127.0.0.1 and 0.0.0.0?
They are not the same.
127.0.0.1 is part of the 127/8 network which is reserved and points to the same computer.
0.0.0.0 is a special IP address that means different things depending on context.
In ...
- 1,231
75
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 ...
- 17.1k
67
votes
Accepted
Why does the “Internet of Things” enforce the need for IPv6 addresses?
The Internet of Things does not absolutely mandate IPv6, but for IoT to be useful or usable IPv6 is very much preferred.
IPv4, due to the limited number of addresses available means that not every ...
- 88k
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 ...
- 3,175
54
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 ...
- 4,498
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 ...
- 415k
50
votes
Accepted
Can a domain name have both IP addresses (IPv6 and IPv4)?
Sure. You have an A record (for IPv4) and an AAAA record (for IPv6). Typically the AAAA record gets resolved first, then the A record.
You can either have just an A name (for an IPv4-only host), AAAA ...
- 126k
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^...
- 60.6k
41
votes
Accepted
Is it OK to use mixed DNS servers (e.g., Google as primary and Quad9 as alternate)?
You are not using "mixed" DNS servers. You have specified a preferred
DNS server, and a alternate fail-back secondary DNS server to be used
if the primary fails to answer.
There is no ...
- 444k
34
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 (...
- 33.8k
31
votes
Accepted
What is the difference between 127.0.0.1 and my assigned IPv4 address?
There's no such thing as "address of the local computer". IP addresses bind with network interfaces. If you have 5 LAN/Wifi cards (network adapters) in your computer then you can have (at least) 5 IPs ...
- 25.5k
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 ...
- 2,044
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 ...
- 34.6k
18
votes
What's the difference between 127.0.0.1 and 0.0.0.0?
127.0.0.1 is one of the addresses of local computer, but any address 127.x.y.z also is another address of the computer (called "loopback address"), except 127.0.0.0 (loopback subnet) and 127.255.255....
- 405
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 ...
- 442
17
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 ...
- 55.5k
16
votes
Why does the “Internet of Things” enforce the need for IPv6 addresses?
There is just one IPv4 address per Network/Router that is connected to
the Internet.
That is not even close to being true. You are seeing things through the eyes of a typical home network user.
...
- 3,355
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 ...
- 34.6k
15
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 ...
- 15.2k
14
votes
Accepted
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 ...
- 415k
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 ...
- 55.5k
12
votes
Can a domain name have both IP addresses (IPv6 and IPv4)?
Yes you can have both IPv4 and IPv6 addresses associated with the same dns name.
As a general rule services should be made available over both ipv4 and ipv6 and the same public facing DNS name used ...
- 5,933
11
votes
Why does the “Internet of Things” enforce the need for IPv6 addresses?
The “Internet of Things” DOES NOT force a need for IPv6. IPv6 is needed even ignoring the IoT - quite simply put, the world is virtually out of IPv4 space, with significant parts of the world not ...
- 67.7k
11
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. ...
- 574
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 ...
- 306
9
votes
What's the difference between 127.0.0.1 and 0.0.0.0?
Typically you use bind-address 0.0.0.0 to allow connections from outside networks and sources. Many servers like MySQL typically bind to 127.0.0.1 allowing only loopback connections, requiring the ...
- 199
9
votes
What is the difference between 127.0.0.1 and my assigned IPv4 address?
Your system can have many ip addresses, and many adaptors, physical or virtual.
Typically you have a loopback adaptor (assigned 127.0.0.1, tho there's actually a block of these) and one or a few more.
...
- 126k
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 ...
- 726
8
votes
Accepted
Leading zeros in IPv4 address; is that a no-no by convention or standard?
There is no standard that demands an IPv4 address be expressed a certain way. That is, the RFC doesn't specify one and multiple formats are in widespread use. Most commonly, you'll see four octets as ...
- 6,262
Only top scored, non community-wiki answers of a minimum length are eligible