1. CS2911 Week 4, Class 2 Today Next Thursday:
15 September 2018
CS2911 Week 4, Class 2
Today
Sit by someone you don't know again!
Review Muddiest Point
DNS – Domain Name Service
Muddiest Point
Next Thursday:
Half Exam 1
17q ,2,5-9,11-15
CS2911
Dr. Yoder
Dr. Josiah Yoder

2. CS2911
15 September 2018
Muddiest Point 4-Lab & 4-2
Why does the chunk size go from hex to ascii back to hex? That seems really inefficient
Encoding in HTTP
Will we get into networking in other languages this class? Or is all the code we write going to by in Python?
Networking in other languages
Is accepting and creating a connection via HTTP made the same way as it is in TCP?
HTTP and TCP
Will the changed exam date affect the date/content of the next quiz (or vice versa)? They are back to back days currently.
Half Exam 1
Joke
Dr. Josiah Yoder

3. Muddiest Point 4-2 What class content should we review for the exam
CS2911
15 September 2018
Muddiest Point 4-2
What class content should we review for the exam
Half-Exam 1 Review
We could use some more guidance on the lab. or an example for the lab. just in a different format. the example would be extremely helpful, without spoiling the answer. This is hard for most of us to do without examples, because most of us have never touched python and never done networking.
Lab 5
Dr. Josiah Yoder

4. Examples for Lab 5
HTTP: look at Wireshark captures to see what your browser does
Python code: Look at your Lab 4 solution. Lab 4 is designed to give you practice at writing Python code like you need for Lab 5
If you feel lost, please come to office hours!!!!
CS2911 Dr. Yoder

5. Questions about Lab 5? HTTP request / response format
How to implement the parser
Python syntax
Encoding/decoding bits/bytes
CS2911 Dr. Yoder

6. Half-Exam 1 Topics See Outcomes
Internet Stack (especially Application and Transport layers)
Binary number system
Binary encoding/decoding T
CS2911 Dr. Yoder

7. Questions on DNS Video
When is the DNS used in the flow of information from the client to the server?
Big picture
where exactly does the code for DNS run?
[server is e.g., BIND, client is e.g., in Python: socket.gethostbyname('google.com') # calls to OS]
Is DNS what modern web browsers use in order to connect to websites? [Yes!] For example lets say you type into your browser, does it use DNS to look up the ip address of Google in order to connect to the website? [Yes!]
CS2911 Dr. Yoder

8. Questions on DNS Video
If canonical names are unique, why are IP addresses necessary?
Big picture
I think the video did a good job, however I'm not sure then how to apply this in code.
CS2911 Dr. Yoder

9. CS2911
15 September 2018
Questions on DNS Video
In the load distribution when there's many different IP addresses, how do you choose the correct one? Is there a single correct one?
Load distribution (choosing IP)
I find the DNS server hierarchy concept a little confusing. Which node is the root server? What do the last tier of servers called and what do they do? Is there a definition for caching?
server hierarchy, caching
Doesn't caching prevent each connection from being distributed properly?
Load distribution (caching)
The video makes the point that there are multiple root level servers and explains how a single would be a major point of failure. Then, it describes how the TLD servers like .com, .edu, etc. are the next level down. Do multiple versions of each of these servers exist? I can't possibly imagine having the .com server crashing and stopping communication to and from all .com websites, but having multiple would lead to a lot more cross-communication.
server hierarchy (single point of failure)
Dr. Josiah Yoder

10. CS2911
15 September 2018
Questions on DNS Video
i am still confused on load distribution. so are there multiple IP for one site? [Yes, for big sites like Google]
Load distribution (multiple IPs)
How does a server store all of these IP addresses and know which one to push forward?
Load distribution (choosing IP)
So when you update your website does that mean there will be a period where the cache is out of date or completely non accessible?
Load distribution (caching)
What is the purpose of rotating the IP addresses? Why should they be in a different order every time? It said that it helps it go to different servers. But I don't understand why they cant be in the same order, and just distribute it among the servers that way. Why the random order?
Load distribution (random order)
Dr. Josiah Yoder

11. Questions on DNS Video
How do MX records work in regards to mail server aliasing? That concept was confusing to me in the video.
MX records
How can the load distribution use on mailing? [Beyond scope of this class]
Load distribution (MX records)
How is bind used and what is it? We know the acronym but not really what it does.
BIND
CS2911 Dr. Yoder

12. CS2911
15 September 2018
Questions on DNS Video
I think I do not have any questions about the part 1(a). For the part a, it mainly talks about what the DNS is and the main software it uses(by using Berkley Internet Name Domain). In addition, the video also talks about four of its main services. However, I have a question about part 1(b). I still feel confused about the relationship between the DNS and the local DNS.
local DNS
What is the equivalent command for dnslookup (the command mentioned in the video that will return the ip given a URL in OS X) in the Windows command prompt?
DNS on Windows
How does the local DNS server work with the DNS server hierarchy?
Dr. Josiah Yoder

13. Questions on DNS Video server hierarchy
Everything was fairly clear. However, I am not exactly sure what BIND is. He never explained that
BIND
Authoritative Servers - source of the official mappings between host names in these domains and the corresponding IP addresses. What is mapping in this context? This concept is unclear.
Mapping domains to IP addresses
The video talks about the use of the BIND software with DNS servers. Could you elaborate on why we use this software.
I'm still slightly confused as to where exactly the DNS is looked up. Does all traffic from every computer around the world go to one server to find the correct IP?
server hierarchy
CS2911 Dr. Yoder

14. Public comments on the videos
The video acknowledged that it wasn't rendered properly, displaying lines not drawn correctly when spelling things out and such. Also, more informative visuals than drawing in real-time might help to convey the message better.
The voice of the narrator is fairly monotonous and boring. I recommend some more images, and a more upbeat person. Try the Crash Course series on Youtube. Very fast, and entertaining.
I thought that the idea of load distribution was really interesting. It seems like a really simple yet effective way to keep a single server from being overloaded.
CS2911 Dr. Yoder

15. Public comments on the videos
The video is good for us to learn some basic knowledge points about the DNS. Especially, it makes us to know that a readable domain name is translated into a specific IP by using DNS(I never know this before).
There wasn't much useful information in that video
The video was ok for introducing the topic however the pacing seemed to be really slow and honestly boring.
He talks really slow. Perhaps speed it up. I played it at 1.5 and it was a lot better. [Thanks for the suggestion! To other students: You can do this by going to the gear on You-tube, and then "Speed." Can either speed up or slow down. You may also want to take notes while watching the videos. That's my strategy for videos I didn't make myself in this class.]
CS2911 Dr. Yoder

16. Public comments on the videos
I think these videos are really good. They are not long and not costing much time to busy MSOE students. I think it is very convenient to get to know some knowledge by using short videos.
The video was overall very well done and provided a good look at what exactly DNS is.
CS2911 Dr. Yoder

17. CS2910
9/15/2018
DNS Record Types
; SOA – Start of Authority example.edu. SOA dns1.example.edu. […] ; NS – Name Server example.edu. NS dns1.example.edu. example.edu. NS dns2.example.edu. ; MX – Mail eXchange server example.edu. MX mail.example.edu.
Adapted from
SE-2811
Dr.Yoder
Dr. Josiah Yoder

18. CS2910
9/15/2018
DNS Record Names (2)
; A – Most basic DNS record dns.example.edu. A mail.example.edu. A ; CNAME – Canonical name mail.example.edu CNAME extern.example.com ; PTR – "pointer" Reverse lookup by IP address in-addr.arpa. PTR dns.example.edu in-addr.arpa. PTR mail.example.edu.
Adapted from
SE-2811
Dr.Yoder
Dr. Josiah Yoder

19. Authoritative Hierarchy
CS2910
9/15/2018
Authoritative Hierarchy
Root DNS Servers
com DNS servers
org DNS servers
edu DNS servers
msoe.edu
DNS servers
umass.edu
yahoo.com
amazon.com
pbs.org
Slide credit: Kurose and Ross, 6th ed. See last slide. (There is a modification )
SE-2811
Dr.Yoder
Dr. Josiah Yoder

20. Local Name Server (Default Name Server)
CS2910
9/15/2018
Local Name Server (Default Name Server)
Not hierarchical
Maintained by an institution or their service provided.
Maintains cache of queries
e.g. ns1.msoe.edu
Exercise: What other role does ns1.msoe.edu play?
SE-2811
Dr.Yoder
Dr. Josiah Yoder

21. CS2911
15 September 2018
CS2911 Dr. Yoder
Dr. Josiah Yoder

22. CS2911
15 September 2018
Acknowledgement
This course is based on the text
Computer Networking: A Top Down Approach 7th edition Jim Kurose, Keith Ross Addison-Wesley
Dr. Josiah Yoder