Author: admin
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6.1 Packet Headers
If you were to look at a packet going across one of many links between its source and destination computers, you would see a link header, an IP header, and a Transport Control Protocol (TCP) header, along with the actual data in the packet. The link header is removed when the packet is received on…
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6. Transport Layer
The next layer up from the Internetworking layer is the Transport layer. A key element of the Internetworking layer is that it does not attempt to guarantee delivery of any particular packet. The Internetworking layer is nearly perfect, but sometimes packets can be lost or misrouted. But users of the network want to reliably send…
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5.5 Questions-Chapter 5
You can take this quiz online at http://www.net-intro.com/quiz/ What does the Domain Name System accomplish? a) It allows network-connected computers to use a textual name for a computer and look up its IP address b) It keeps track of the GPS coordinates of all servers c) It allows Regional Internet Registries (RIRs) to manage IP…
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5.4 Glossary-Chapter 5
DNS: Domain Name System. A system of protocols and servers that allow networked applications to look up domain names and retrieve the corresponding IP address for the domain name. domain name: A name that is assigned within a top-level domain. For example, khanacademy.org is a domain that is assigned within the “.org” top-level domain. ICANN:…
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5.3 Summary
While the Domain Name System is not one of our four layers in the model, it is an important part of making the Internet easier to use. Domain names allow end users to use symbolic names for servers instead of numeric Internet Protocol addresses. By adding a service that maps domain names to IP addresses,…
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5.2 Reading Domain Names
When we look at an IP address like “212.78.1.25”, the left prefix is the “Network Number”, so in a sense we read IP addresses from left to right, where the left part of the IP address is the most general part of the address and right part of the address is most specific: 212.78.1.25 Broad…
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5.1 Allocating Domain Names
If you recall from the previous section, IP addresses are allocated based on where you connect a new network to the Internet. Domain names are allocated based on organizations that “own” the domain name. At the top of the domain name hierarchy is an organization called the International Corporation for Assigned Network Names and Numbers(ICANN).…
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5. The Domain Name System
The Domain Name System lets you access websites by their domain name like (www.khanacademy.org), so you don’t have to keep a list of numeric Internet Protocol (IP) addresses like “212.78.1.25”. IP address are determined by where your computer connects to the Internet. When you have a portable computer and you move from one location to…
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4.9 Glossary-Chapter 4
core router: A router that is forwarding traffic within the core of the Internet. DHCP: Dynamic Host Configuration Protocol. DHCP is how a portable computer gets an IP address when it is moved to a new location. edge router: A router which provides a connection between a local network and the Internet. Equivalent to “gateway”.…
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4.8 Summary Chapter 4
The Internetworking Protocol layer extends our network from a single hop (Link layer) to a series of hops that result in packets quickly and efficiently being routed from your computer to a destination IP address and back to your computer. The IP layer is designed to react and route around network outages and maintain near-ideal…
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4.7 Global IP Address Allocation
If you wanted to connect the network for a new organization to the Internet you would need to contact an Internet Service Provider and make a connection. Your ISP would give you a range of IP addresses (i.e., one or more network numbers) that you could allocate to the computers attached to your network. The…
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4.6 A Different Kind of Address Reuse
If you know how to find the IP address on your laptop, you can do a little experiment and look at the different IP addresses you get at different locations. If you made a list of the different addresses you received at the different locations, you might find that many of the locations give out…
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4.5 Getting an IP Address
Increasingly, computers are portable or mobile. We just pointed out how important it was for the IP layer to track large groups of computers using network numbers instead of tracking every single computer individually. But since these network numbers indicate a particular physical connection to the network, when we move a computer from one location…
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4.4 Determining Your Route
There is no place in the Internet that knows in advance the route your packets will take from your computer to a particular destination. Even the routers that participate in forwarding your packets across the Internet do not know the entire route your packet will take. They only know which link to send your packets…
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4.3 When Things Get Worse and Better
Sometimes the network has problems and a router must find a way to route data around the problems. A common problem is that one of the outbound links fails. Perhaps someone tripped over a wire and unplugged a fiber optic cable. At this point, the router has a bunch of network numbers that it wants…