171
votes
Accepted
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 ...
- 97.7k
87
votes
Accepted
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 ...
- 16.6k
82
votes
Accepted
Why do we need IPv6?
Two things are getting confused here:
classful addressing vs CIDR
Masquerading / NAT
Going from classful addressing to Classless Inter Domain Routing (CIDR) was an improvement that made the address ...
- 6,670
56
votes
Accepted
TCPDump - Filter by MAC Address
You have used the following as your packet filter: host aa:bb:cc:11:22:33
As it stands, this is looking for an IP or hostname but you are giving it a MAC address.
To use a MAC address, you need to ...
- 27.1k
55
votes
Accepted
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 ...
- 97.7k
40
votes
Accepted
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 }
...
- 19.3k
37
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 ...
- 470
33
votes
Does CIDR really "do away" with IP address classes?
classful addressing is "a thing of the past".
This is true because nothing in the modern internet does classful addressing[1]. With classful addressing, the netmask is a fixed value based on the ...
- 31.1k
33
votes
Accepted
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 ...
- 79.7k
33
votes
Accepted
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 ...
- 16.6k
31
votes
Accepted
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 ...
- 989
29
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. ...
- 79.7k
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 ...
- 97.7k
28
votes
Accepted
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 ...
- 97.7k
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 ...
- 97.7k
27
votes
Accepted
Does CIDR really "do away" with IP address classes?
Address delegation really used to happen in three sizes: class A, B and C. Class A delegations would be given from a certain address range, class B delegations from a different range etc. Because the ...
- 6,670
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....
- 370
24
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, ...
- 97.7k
23
votes
Accepted
What do TCP/UDP add to "raw ip"?
IP is a Layer 3 protocol. TCP/UDP are Layer 4 protocols. They each serve different purposes.
Layer 3 is in charge of end to end delivery. Its sole function is adding whatever is necessary to a packet ...
- 14.5k
23
votes
Accepted
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 ...
- 16.6k
22
votes
Accepted
What is Link-local addressing?
I never seen 169.254/16 working in IPv4.
A PC automatically acquires a 169.254.x.x/16 address if it does not receive an IP address from a DHCP server. If you disable the DHCP server on your home or ...
- 2,337
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 ...
- 97.7k
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 ...
- 97.7k
22
votes
Accepted
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 ...
- 436
20
votes
How do you calculate the prefix, network, subnet, and host numbers?
The answer above hits the nail on the head perfectly. However, when I first started out, it took me a few different examples from a couple of sources for it to really hit home. Therefore, if you're ...
- 2,337
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 ...
- 4,477
20
votes
Accepted
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 ...
- 79.7k
19
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 ...
- 97.7k
19
votes
Accepted
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:
...
- 97.7k
19
votes
Accepted
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 ...
- 97.7k
Only top scored, non community-wiki answers of a minimum length are eligible