Talk:Web Science/Part1: Foundations of the web/Domain Name System/Review some facts about DNS
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Check your understanding clarification[edit source]
- A domain can be resolved either to an IPv4 or an IPv6 address.
Why is it false? We can have either A or AAAA record in a DNS record.
- of course you can have BOTH. I think this is a language problem. Either OR means to have something like an XOR so either the one or the other. --Renepick (discuss • contribs) 08:13, 4 November 2013 (UTC)
- IP routing is hierarchical.
Why is it false? In routing packages we do not care about the destination IP (if it is not in our network), we care only about the network which can forward our package. It means we have a hierarchy. Or I misunderstood something? --oleamm (discuss • contribs) 03:53, 4 November 2013 (UTC)
- how would you best define hierarchy? If you have a packat for let's say network 184.108.40.206 and you are in some other network and don't have an entry for 220.127.116.11 in your routing table you send the packet to your default route this could be network 18.104.22.168 but if you are in another network you default route could first send you to 22.214.171.124. So I don't see how an hierarchy comes into play. There is not this one central top level network to which to send our packet if we don't know a route and which will start to trickle everything down. --Renepick (discuss • contribs) 08:13, 4 November 2013 (UTC)
- It's a tricky question. But we had classful networks and it's already a hierarchy. We have at least 2 level of hierarchy - a host (bottom level) and a network (upper level).
Most Transmission Control Protocol/Internet Protocol (TCP/IP) routing is based on a two-level hierarchical routing in which an IP address is divided into a network portion and a host portion. Gateways use only the network portion until an IP datagram reaches a gateway that can deliver it directly. Additional levels of hierarchical routing are introduced by the addition of subnetworks. Source: Hierarchical routing.
Information from the video[edit source]
Review some DNS facts
What DNS is and what it is not?
First of all DNS is simply database of answers to questions about the points in the hierarchy. For example, does the eng.xyz.com domain have an address, does it has any mail services associated with it, is it known by other names? These are questions that DNS is designed to answer.
Secondly, DNS is NOT geography. DNS has nothing about physical locations. Two machines may be in the same domain but they are not necessarily anywhere near each other. That’s why google, amazon work so well. We just type an address like youtube.com in the web browser but the web page we got back could come from anyone of thousands web servers that are all around the planet.
Finally, DNS is NOT the same as IP routing. The way that packets are routing arouns the Internet using the IP address is very different. Unlike DNS, IP is not hierarchical. Machine’s IP address tells you nothing about the Domain name that it sent. And vice versa: we may assume that all machines under the same domain name have similar IP addresses.
--Jane Kruch (discuss • contribs) 20:57, 6 November 2013 (UTC)