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 ...
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  • 15.6k
31 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 ...
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  • 69.5k
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 ...
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  • 92.8k
26 votes
Accepted

Is it common for ISPs to connect to each other directly?

Yes, this does happen quite a lot, and it is called private peering. It has some benefits over peering over an IXP: dedicated bandwidth, you can be sure you can use the full capacity of the ...
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  • 15.6k
22 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 ...
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  • 406
19 votes
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Internet Cable Has Been cut in two and taped back together

This can introduce a number of problems, like additional attenuation or cross talk. Splicing is to be avoided whenever possible, but I have seen this work in a pinch although I would never recommend ...
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  • 26.7k
17 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 ...
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  • 522
16 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 ...
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14 votes
Accepted

How do routers on the backbone avoid IP address conflicts?

The RIRs assign addressing to the ISPs. An ISP not following the rules will quickly find itself ostracized and cut off from the rest of the Internet. IANA owns the addressing and assigns each of the ...
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  • 92.8k
12 votes
Accepted

Who pays for traffic when it transits multiple providers

EDIT: I forgot to mention this - if you're interested, there have been books written about this topic. I highly recommend Bill Norton's The Internet Peering Playbook. Available in print or digital ...
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  • 8,837
12 votes

What stops someone from configuring their network with IP addresses they do not own?

What stops them from attributing their routers and hosts already in use IP addresses? Nothing. Over the years, I have seen both organizations of all sizes, both public and private, do this including ...
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  • 26.7k
11 votes

Do Bluetooth Devices have MAC address with the same specification as the MAC addresses of the Ethernet and Wi-Fi Network cards?

Bluetooth devices are required to have a unique device address, assigned from the same registry as Ethernet and Wifi MAC addresses. Quoting the Bluetooth specification version 5.0 volume 1: Each ...
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  • 243
10 votes
Accepted

Smallest IPv6 block advertised?

Yes. Nobody will advertise any network smaller than a /48. The same thing is in IPv4; no ISP will advertise any network smaller than a /24. The problem is the sheer number of routes that would ...
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  • 92.8k
10 votes
Accepted

How are IPv4 Addresses provided uniquely to domains?

Who mainly provides IP addresses to domains? As in, who commands, "www.google.com, 103.233.38.93 is yours; www.stackexchange.com I will assign 104.16.115.182 to you; etc." Normally IP addresses are ...
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  • 11.6k
9 votes

How can I calculate the number of internet routes myself?

In addition to the good answers already given by Jens Link and Ron: There's no absolute, objective answer how many routes are active on the internet. The number constantly changes due to networks ...
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  • 15.6k
9 votes
Accepted

Analyze Network Traffic by Autonomous System Number?

You can certainly do this with Wireshark. In the menu choose Statistics > Endpoints and you will see a window like this: You might need to copy and paste into Excel to sum the bytes per AS, or use ...
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  • 15.9k
8 votes
Accepted

How can I calculate the number of internet routes myself?

The backbone routers of ISPs (to be precise, Tier-1 ISPs) constitute what is known as the "default-free zone." In this zone, there are no default routes -- every route that is announced on the ...
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  • 62k
8 votes

using fiberoptic for long-distance ethernet connection

Part 1: Using fiber to run a 1000 foot ethernet link Using fiber to run a long ethernet link is not quite as simple as you make out but it's certainly not unreasonable to DIY. A few things you have ...
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  • 11.6k
8 votes
Accepted

Finding Subnet Ranges of IPv6

Basically, with IPv6, most subnets will just be /64. Using subnets of other sizes, with a couple of exceptions, will break features of IPv6. See RFC 5375, IPv6 Unicast Address Assignment ...
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  • 92.8k
8 votes
Accepted

Private IP inside internet?

Traceroute deliberately sends packets with low time-to-live values to make the routers between you and your destination send back ICMP TTL exceeded messages. The traceroute output is basically the ...
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  • 4,591
8 votes
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Why is the internet *not free?

Most ISPs have to buy service from other ISPs to be able to reach every part of the internet. That is called "transit". If you start a small ISP you usually buy transit from one or more bigger ISPs. ...
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8 votes
Accepted

When X.25 or ATM were used in ISP networks or Internet backbone was the protocol running over this layer still TCP/IP?

Think of it this way: we used the fastest links we could buy to run IP over the wide area between the nodes of the Internet. So that was 56/48Kbps X.25, and later 1.44/2Mbps Frame Relay, and later ...
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  • 1,161
8 votes
Accepted

What's the domain of an IP?

It is a routing domain. That is a block of addressing controlled by a single entity. For example, Company X could be assigned 10.11.0.0/23, Company Y could be assigned 10.11.2.0/23, and Company Z ...
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  • 92.8k
8 votes
Accepted

Class A most significant bits '0' as in RFC1166 or older or '00' as suggested in RFC4632?

It appears to be a typo in that RFC. Notice that the header of the RFC says Errata Exist. It is not uncommon for things like that to happen. That particular error is corrected in the errata. See the ...
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  • 92.8k
8 votes
Accepted

Is it true that the fd00::/8 address range (ULA) in ipv6 is for machines that you NEVER want to speak with anything on the Internet?

IPv6 packets addressed in the IPv6 ULA address range, fc00::/7, can not be routed on the public Internet. Remember, though, that interfaces can have multiple IPv6 addresses, including Link-Local, ...
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  • 92.8k
8 votes
Accepted

Is QoS an issue for VOIP calls over the Internet? If not, why not?

VoIP over the public Internet can be a problem, but it usually works good enough, most of the time, although there can be times where it sucks. Most ISPs have extra cost features where they will honor ...
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  • 92.8k
8 votes

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

A device that has an IP address exists within a network. A Router is a device who's primary purpose is to pass traffic between networks. For a Router to pass packets between two networks, it must ...
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  • 13.9k
8 votes

What stops someone from configuring their network with IP addresses they do not own?

Nothing will stop them using the addresses on their own machines. What happens if they try to advertise them to the Internet depends on how sloppy their providers are. If their providers are ...
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  • 11.6k
8 votes

Is a point-to-point T1 line literally a line in real life?

No. There may be a dedicated circuit between the routers and the nearest telco central office, but between offices they are switched and multiplexed onto other, higher capacity circuits. Today, most ...
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