Addresses on the Web
- Terminology and concepts to look out for: URL · domain name · DNS
- Relevance to me: Yesterday you learned that a site lives on a host. Today you learn what the parts of a web address mean and how a browser uses one to find that host.
- Board Question: How does a browser find the right computer out of all the computers on the internet? Write your best explanation in two or three sentences, and circle the step you are least sure about.
Open the discussion form on the right and answer Section 1 from your first reading.
Web Addresses and DNS
This section explains the parts of a web address and how a browser uses one to find the host that holds a site.
Hosts on the Internet
As Monday's lesson explained, a site's files have to be deployed to a host that is on the internet before other people can open the site. A host is a server that is always on and connected to the internet, and it stores a site's files and sends them to the browsers that ask for them. Other machines find a device on the internet by its IP address, and every connected device has one. An IP address in the older form, called IPv4, is four numbers separated by dots, such as 104.21.7.78, and the newer IPv6 form is longer and uses numbers and letters separated by colons.
The Parts of a URL
A URL is the full address of one page or file on the web, and the letters stand for Uniform Resource Locator. A URL has three main parts, and they always appear in the same order. The first part is the scheme, which names the method the browser uses to ask for the page, and most sites use the scheme https. The second part is the domain name, which names the host, and the third part is the path, which tells the host which page or file the browser wants. Figure 1 splits the address of today's bench, shown below, into these three parts.
https://muggsofcompsci.net/cs1/bench/b17
In this URL, the scheme is https, followed by the characters ://, the domain name is muggsofcompsci.net, and the path is /cs1/bench/b17. The path works like the file paths from the Nov 9 lesson, because it names each step of the route with a slash between the steps. MDN, a guide for web builders, explains that a path once named a real file stored on the host, and that today it is often only a name the host uses to choose what to send. For that reason, a path names a page or a file. Every bench in this class shares one domain name, and only the path changes, from /cs1/bench/b17 today to /cs1/bench/b18 tomorrow. A domain name alone is not a full URL, because the name muggsofcompsci.net tells a browser which host to reach but gives no scheme and no path, so it does not point to one page.
Domain Names and DNS
A domain name is a name that stands for a host, so that people can type words where computers use numbers. MDN notes that IP addresses are hard to remember and can change over time. A domain name is not the host itself, because the host is a computer and the domain name is a label that is matched to that computer's IP address.
DNS, the Domain Name System, is the system that finds the IP address for a domain name. Figure 1 shows the steps in order. First, the browser asks DNS for the IP address that matches the domain name in the URL. Next, DNS returns the IP address, and then the browser sends its request to that IP address, with the path inside the request. Finally, the host sends the page back to the browser. A computer also keeps recent answers for a short time, so it does not have to ask DNS again for every page. DNS does not hold a site's pages, because it only answers the question of which address a name belongs to.
DNS replaced an older method of matching names to addresses. RFC 1034, a 1987 document that describes DNS, explains that the names and addresses of hosts were once kept in a single file called HOSTS.TXT, and every host had to copy it. The work of sending out new copies grew quickly as the network grew, so the designers built a distributed database, which is a set of records spread across many servers.
A Real Lookup
The lookup below was made for muggsofcompsci.net on Oct 19, 2026, with a command called Resolve-DnsName on a Windows computer.
Name Type TTL Section IPAddress ---- ---- --- ------- --------- muggsofcompsci.net A 300 Answer 172.67.135.225 muggsofcompsci.net A 300 Answer 104.21.7.78
DNS returned two IPv4 addresses for one domain name, 172.67.135.225 and 104.21.7.78, and a second lookup on the same day also returned two longer IPv6 addresses. Both IPv4 addresses belong to Cloudflare, the company whose servers answer for the class site. A domain name can point to more than one IP address, and the browser needs only one of them to send its request. A lookup on another day may return different addresses, because the addresses behind a name can change.
Summary
A URL is the full address of one page or file, and its three main parts are the scheme, the domain name and the path. A domain name stands for a host, and DNS finds the IP address for that domain name. The browser then sends its request to that IP address, and the path tells the host which page or file to send.
Sources: MDN, What is a URL? (2026); MDN, What is a domain name? (2025); Cloudflare, What is DNS? (n.d.); Cloudflare, What is my IP address? (n.d.); Cloudflare, IP Ranges (n.d.); Cloudflare, What is round-robin DNS? (n.d.); Mockapetris, RFC 1034 (1987); course passage, Files, Folders and File Paths (2026); course passage, Hosts, Deploys and Static Sites (2026); classroom data, DNS lookup and bench address check (2026).
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notebook cue: URL
In today's bench address, which part is the path, and what does it ask the host for?
Check
The path is /cs1/bench/b17, the part after the domain name. It tells the host which page the browser wants, which is today's bench, B17. See The Parts of a URL, paragraphs 1 and 2, and Figure 1.
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notebook cue: domain name
Why do people use domain names when computers use IP addresses?
Check
IP addresses are numbers that are hard to remember and can change over time, so people type a domain name, a name that stands for the host. DNS then finds the IP address the computer needs. See Domain Names and DNS, paragraph 1.
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notebook cue: DNS
Put these in order: the browser sends its request to the host; the browser asks DNS; DNS returns an IP address.
Check
First, the browser asks DNS. Next, DNS returns an IP address. Then the browser sends its request to the host at that IP address. See Domain Names and DNS, paragraph 2, and steps 1 to 3 of Figure 1.
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notebook cue: URL
In today's bench address, which part is the path, and what does it ask the host for?
Check
The path is /cs1/bench/b17, the part after the domain name. It tells the host which page the browser wants, which is today's bench, B17. See The Parts of a URL, paragraphs 1 and 2, and Figure 1.
-
notebook cue: domain name
Why do people use domain names when computers use IP addresses?
Check
IP addresses are numbers that are hard to remember and can change over time, so people type a domain name, a name that stands for the host. DNS then finds the IP address the computer needs. See Domain Names and DNS, paragraph 1.
-
notebook cue: DNS
Put these in order: the browser sends its request to the host; the browser asks DNS; DNS returns an IP address.
Check
First, the browser asks DNS. Next, DNS returns an IP address. Then the browser sends its request to the host at that IP address. See Domain Names and DNS, paragraph 2, and steps 1 to 3 of Figure 1.
Web Addresses and DNS
This section explains the parts of a web address and how a browser uses one to find the host that holds a site.
Hosts on the Internet
As Monday's lesson explained, a site's files have to be deployed to a host that is on the internet before other people can open the site. A host is a server that is always on and connected to the internet, and it stores a site's files and sends them to the browsers that ask for them. Other machines find a device on the internet by its IP address, and every connected device has one. An IP address in the older form, called IPv4, is four numbers separated by dots, such as 104.21.7.78, and the newer IPv6 form is longer and uses numbers and letters separated by colons.
The Parts of a URL
A URL is the full address of one page or file on the web, and the letters stand for Uniform Resource Locator. A URL has three main parts, and they always appear in the same order. The first part is the scheme, which names the method the browser uses to ask for the page, and most sites use the scheme https. The second part is the domain name, which names the host, and the third part is the path, which tells the host which page or file the browser wants. Figure 1 splits the address of today's bench, shown below, into these three parts.
https://muggsofcompsci.net/cs1/bench/b17
In this URL, the scheme is https, followed by the characters ://, the domain name is muggsofcompsci.net, and the path is /cs1/bench/b17. The path works like the file paths from the Nov 9 lesson, because it names each step of the route with a slash between the steps. MDN, a guide for web builders, explains that a path once named a real file stored on the host, and that today it is often only a name the host uses to choose what to send. For that reason, a path names a page or a file. Every bench in this class shares one domain name, and only the path changes, from /cs1/bench/b17 today to /cs1/bench/b18 tomorrow. A domain name alone is not a full URL, because the name muggsofcompsci.net tells a browser which host to reach but gives no scheme and no path, so it does not point to one page.
Domain Names and DNS
A domain name is a name that stands for a host, so that people can type words where computers use numbers. MDN notes that IP addresses are hard to remember and can change over time. A domain name is not the host itself, because the host is a computer and the domain name is a label that is matched to that computer's IP address.
DNS, the Domain Name System, is the system that finds the IP address for a domain name. Figure 1 shows the steps in order. First, the browser asks DNS for the IP address that matches the domain name in the URL. Next, DNS returns the IP address, and then the browser sends its request to that IP address, with the path inside the request. Finally, the host sends the page back to the browser. A computer also keeps recent answers for a short time, so it does not have to ask DNS again for every page. DNS does not hold a site's pages, because it only answers the question of which address a name belongs to.
DNS replaced an older method of matching names to addresses. RFC 1034, a 1987 document that describes DNS, explains that the names and addresses of hosts were once kept in a single file called HOSTS.TXT, and every host had to copy it. The work of sending out new copies grew quickly as the network grew, so the designers built a distributed database, which is a set of records spread across many servers.
A Real Lookup
The lookup below was made for muggsofcompsci.net on Oct 19, 2026, with a command called Resolve-DnsName on a Windows computer.
Name Type TTL Section IPAddress ---- ---- --- ------- --------- muggsofcompsci.net A 300 Answer 172.67.135.225 muggsofcompsci.net A 300 Answer 104.21.7.78
DNS returned two IPv4 addresses for one domain name, 172.67.135.225 and 104.21.7.78, and a second lookup on the same day also returned two longer IPv6 addresses. Both IPv4 addresses belong to Cloudflare, the company whose servers answer for the class site. A domain name can point to more than one IP address, and the browser needs only one of them to send its request. A lookup on another day may return different addresses, because the addresses behind a name can change.
Summary
A URL is the full address of one page or file, and its three main parts are the scheme, the domain name and the path. A domain name stands for a host, and DNS finds the IP address for that domain name. The browser then sends its request to that IP address, and the path tells the host which page or file to send.
Sources: MDN, What is a URL? (2026); MDN, What is a domain name? (2025); Cloudflare, What is DNS? (n.d.); Cloudflare, What is my IP address? (n.d.); Cloudflare, IP Ranges (n.d.); Cloudflare, What is round-robin DNS? (n.d.); Mockapetris, RFC 1034 (1987); course passage, Files, Folders and File Paths (2026); course passage, Hosts, Deploys and Static Sites (2026); classroom data, DNS lookup and bench address check (2026).
Each table agrees on one explanation and names the step it is least sure about.
Chromebooks stay closed while your table talks. Sections 1 and 2 of the discussion form are already done. After you talk, finish Section 3 right here under My View. Submit before the exit ticket.
This form has three sections. Section 1: answer today's Board Question. Section 2: after the reading. Section 3 opens later in class. Today's Board Question: How does a browser find the right computer out of all the computers on the internet? Write your best explanation in two or three sentences, and circle the step you are least sure about.
CR 1. Board Question: How does a browser find the right computer out of all the computers on the internet? Write your best explanation in two or three sentences, and circle the step you are least sure about. Give your answer and one reason.
Write your answer in your lab notebook, labeled CR 1.
MC 1. Think about your answer to the board question. How does a browser find the right computer out of all the computers on the internet? Write your best explanation in two or three sentences, and circle the step you are least sure about. Which position is closest to yours now?
- The browser already knows where every website is.
- The browser asks DNS for the IP address that matches the name, then sends its request there.
- The browser searches for the name and opens the first result.
MC 2. (Reading claim 1) Every host on the internet has an IP address.
- Agree
- Disagree
MC 3. (Reading claim 2) Each domain name matches exactly one IP address.
- Agree
- Disagree
MC 4. (Reading claim 3) The path in a URL tells the host which page or file the browser wants.
- Agree
- Disagree
MC 5. (Reading claim 4) The three main parts of a URL are the scheme, the domain name and the path, in that order.
- Agree
- Disagree
MC 6. (Reading claim 5) In Figure 1, the browser sends its request to the host before it asks DNS for an IP address.
- Agree
- Disagree
MC 7. (Reading claim 6) A domain name and an IP address are the same thing.
- Agree
- Disagree
MC 8. (Reading claim 7) Each bench in this class has its own domain name.
- Agree
- Disagree
MC 9. (Reading claim 8) In Reading 2, the lines inside greet run first, because greet is written above main.
- Agree
- Disagree
CR 2. (A different view) Write the view at your table that was most different from yours. If everyone agreed, write the strongest argument against your table's answer.
Write your answer in your lab notebook, labeled CR 2.
CR 3. Think about the Board Question again: How does a browser find the right computer out of all the computers on the internet? Write your best explanation in two or three sentences, and circle the step you are least sure about. Do you have the same opinion as when you first answered the board question? If it is the same, what from the reading or table talk reaffirmed your opinion? If it is different, what from the reading or table talk changed your opinion?
Write your answer in your lab notebook, labeled CR 3.