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174 votes
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Why are IPv4 addresses running out?

The IPv4 Address Shortage According to Vint Cerf (the father of IP), the IPv4 32-bit address size of was chosen arbitrarily. IP was a government/academic collaborative experiment, and the current ...
Ron Maupin's user avatar
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87 votes
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Is "IPv10" a joke or a serious RFC draft?

As Ron said, anyone can write a proposal. I have a hard time taking proposals seriously from someone who suggests interconnecting satellites with optical fiber, though. Also, I can't imagine this ...
Teun Vink's user avatar
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58 votes
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Why does the IPv6 header not include a checksum?

One of the ideas around IPv6 was to speed up packet forwarding. To that end, several decisions were made. For example, the IPv6 header was greatly simplified and is a fixed length, unlike the variable ...
Ron Maupin's user avatar
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40 votes
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What is the difference between 0.0.0.0 and a loopback IP address?

The statement: The IP address 0.0.0.0 [...] means ‘‘this network’’ or ‘‘this host.’’ is misleading. It is not a "or" but "This host on this network." From RFC1122: { 0, 0 } ...
JFL's user avatar
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39 votes

Why are IPv4 addresses running out?

Ron Maupin's answer gives a brilliant overview of the IPv4 shortage, but I'd like to address this part of your question: Why can't a city (for example) have just one IP address and all homes in ...
IMSoP's user avatar
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33 votes
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Why are IP addresses given to each interface and not device? What would the implications of that be?

Connecting an interface to a network makes it a part of that network. Therefore, the IP address is a property of the connection, not the host. Likewise, a host can have many network connections and ...
Zac67's user avatar
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33 votes
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What stops someone from configuring their network with IP addresses they do not own?

Most likely if they're a big university they are their own ISP, using BGP to connect their network to the internet via a number of upstream networks. Nothing stops them from using IP addresses they ...
Teun Vink's user avatar
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31 votes
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Is multicast on the public internet possible? And if yes: How?

You cannot multicast on the public Internet, but you can multicast across the public Internet to another site by using a tunnel that supports multicast. Multicast routing is very different from ...
Ron Maupin's user avatar
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31 votes
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Will IPv6 make private IP addresses become obsolete?

No, private addressing will not become obsolete. But actually, there are two kinds of private addresses: the Unique Local Addresses (ULAs) and the link-local addresses (LLAs). There will always be a ...
KillianDS's user avatar
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30 votes

How is 8 bits sufficient for the TTL in an IP header?

Even when sending packets across continents, a TTL of 255 is more than enough - there simply aren't more routers involved. Running a quick test (from Germany) shows 17 hops to the US and 18 to Japan. ...
Zac67's user avatar
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28 votes

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

Part 1 of 2 IPv4 Math With an IPv4 address and the network mask, the network mask length, or host mask, you can calculate the Network Address, Broadcast Address, Total Addresses, Usable Addresses, ...
Ron Maupin's user avatar
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28 votes

Is "IPv10" a joke or a serious RFC draft?

You must remember that anyone can submit proposals to the IETF, and they are taken seriously, until they are either adopted or die due to lack of interest. This particular proposal has expired and ...
Ron Maupin's user avatar
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28 votes

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

A /31 network actually has two usable hosts for a point-to-point link. See the Standards Track RFC 3021, Using 31-Bit Prefixes on IPv4 Point-to-Point Links (published in December 2000): Abstract With ...
Ron Maupin's user avatar
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27 votes

Why does the IPv6 header not include a checksum?

Because it's redundant. All the common link-layer protocols, like Ethernet or WiFi, have their own error checking and error correction mechanisms, so physical transmission errors are already unlikely....
Philipp's user avatar
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24 votes
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Why isn't multicasting more popular?

Because multicast is one source to many receivers, and thus two way communications (and anything using TCP connections) won't work. That makes it unfit to use for teleconferencing, online ...
Teun Vink's user avatar
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22 votes

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

Continued from Part 1... Part 2 of 2 Subnet IPv4 Networks Subnetting a network is creating multiple, longer networks from a network address and mask. The basic idea is that you borrow high-order ...
Ron Maupin's user avatar
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22 votes

Does every host on the LAN share the same ARP table, or do hosts keep them individually?

Actually, every interface in a device has its own ARP table. A host could have several ARP tables (one for each interface it has). ARP tables are not shared between hosts, or even among interfaces in ...
Ron Maupin's user avatar
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22 votes

Difference between :: and ::1

:: is the unspecified address (0:0:0:0:0:0:0:0), and it is only used in packets as the source address of a host that does not yet have an address and is trying to get an address assigned. What you see ...
Ron Maupin's user avatar
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21 votes
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Is it possible to specify a route for a packet to take?

It's theoretically possible, but not really in a practical sense. The IP protocol includes two options: Loose Source and Record Route (LSRR) Strict Source and Record Route (SSRS) They're both ...
Barmar's user avatar
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20 votes
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IPv4 Segment 100.64.0.0/10

The 100.64.0.0/10 address block is not private address space; it is shared address space. This is spelled out in RFC 6598, IANA-Reserved IPv4 Prefix for Shared Address Space (I highlighted the ...
Ron Maupin's user avatar
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20 votes

Where can I use the IPv6 documentation prefix

The IPv6 documentation prefix (2001:db8:::/32) must be used ONLY for documentation purposes. It means written examples, diagrams, PPT presentations, Textbook explanations, etc. This range shouldn't ...
jcbermu's user avatar
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20 votes
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Is the MTU of Ethernet still 1500 Bytes?

Standard maximum payload size for Ethernet is still 1500 bytes. While the maximum frame size has grown slightly, from 1518 to 1522 byte with 802.1Q and further with 802.1AD, the payload, "MAC client ...
Zac67's user avatar
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19 votes
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Why are there 3 ranges of private IPv4 addresses?

Back when the RFC for private addressing was proposed, classful addressing was still common. The reasons for the three address ranges are found in RFC 1918, Address Allocation for Private Internets: ...
Ron Maupin's user avatar
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19 votes
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What happens when a subnet reaches capacity?

A subnet (network) is really just a collection of contiguous addresses within a binary mask. It is simply a logical way to divide address block. If you run out of addresses in a network (subnet), then ...
Ron Maupin's user avatar
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19 votes

Is "IPv10" a joke or a serious RFC draft?

Is “IPv10” a joke or a serious RFC draft? Both. That draft doesn't solve a single problem but opens a can of new ones. I guess that bloke is serious and he doesn't get what ridiculous schemes he's ...
Zac67's user avatar
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19 votes

Is multicast on the public internet possible? And if yes: How?

As an end-user, you cannot multicast across the Internet, unless using a tunnel. As a larger organization, like a video provider or an ISP, it is certainly possible to forward multicast packets ...
pHeoz's user avatar
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19 votes
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Is there anything stopping me from using Class A addresses on my own network?

As long as you are translating your "15.0.0.0" address space to something unique on the Internet that doesn't overlap, things will "work fine". However, you won't be able to ...
Eddie's user avatar
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17 votes

Why are IP addresses given to each interface and not device? What would the implications of that be?

It would not be enough. Suppose I have a computer with three interfaces: eth0 (wired Ethernet), wlan0 (wifi), and vboxnet0 (virtualbox). One of the interfaces is connected to an internal network, one ...
Piskvor left the building's user avatar
17 votes

IP addresses from public IP block in my LAN

EDITED I'm assuming you're considering using an IP block that is not registered to you. Otherwise, skip to the last paragraph. Besides being a very poor practice, if you use public addresses on your ...
Ron Trunk's user avatar
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17 votes
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Why the first octet of a MAC address always end with a binary 0?

You may notice that two least-significant bits of the most-significant byte of a 48-bit MAC address are usually set to 0 (as in all your examples). There are two flags in the most-significant byte of ...
Ron Maupin's user avatar
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