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Problem 1 Suppose you have a new computer just set up. dig is one of the most useful DNS lookup tool. You can check out the manual of dig at http://linux.die.net/man/1/dig. A typical invocation of dig looks like: dig @server name type. Suppose that on April 19, 2017 at 15:35:21, you have issued…
Problem 1
Suppose you have a new computer just set up. dig is one of the most useful DNS lookup tool. You can check out the manual of dig at http://linux.die.net/man/1/dig. A typical invocation of dig looks like: dig @server name type.
Suppose that on April 19, 2017 at 15:35:21, you have issued \dig google.com a” to get an IPv4 address for google.com domain from your caching resolver and got the following result: (If a user just types “dig google.com” the default is type=A)
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 17779
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 4, ADDITIONAL: 4
;; QUESTION SECTION: | ||||
;google.com. | IN | A | ||
;; ANSWER SECTION: | ||||
google.com. | 239 | IN | A | 172.217.4.142 |
;; AUTHORITY SECTION: | ||||
google.com. | 55414 | IN | NS | ns4.google.com. |
google.com. | 55414 | IN | NS | ns2.google.com. |
google.com. | 55414 | IN | NS | ns1.google.com. |
google.com. | 55414 | IN | NS | ns3.google.com. |
;; ADDITIONAL SECTION: | ||||
ns1.google.com. | 145521 | IN | A | 216.239.32.10 |
ns2.google.com. | 215983 | IN | A | 216.239.34.10 |
ns3.google.com. | 215983 | IN | A | 216.239.36.10 |
ns4.google.com. | 215983 | IN | A | 216.239.38.10 |
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Problem 2
Suppose that you walked into Boelter Hall and get connected to CSD WiFi network, which automatically gave you IP address of the local caching resolver. However, initially, it doesn’t allow you to do anything unless you type your username and password in a popup window (or if you try to go to any website in your browser).
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Problem 3
Same context as Problem 2. After you successfully logged in, you can start using the Internet. Suppose the caching resolver has just rebooted and its cache is completely empty; RTT between your computer and the caching resolver is 10ms and RTT between the caching resolver and any authoritative name server is 100ms; all responses have TTL 12 hours.
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Problem 4
How does SMTP mark the end of a message body? How about HTTP? Can HTTP use the same method as SMTP to mark the end of a message body? Explain.
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Problem 5
Consider the following environment with a local DNS caching resolver and a set of authoritative DNS name servers.
Assume that initially,
the caching resolver cache is empty, TTL values for all records is 1 hour,
RTT between stub resolvers (hosts A, B, and C) and the caching resolver is 20 ms,
RTT between the caching resolver and any of the authoritative name servers is 150 ms, There are no packet losses,
All processing delays are 0 ms
root domain
edu. com.
google.com. amazon.com.
caching resolver
A
B
C
google.com. | 3600 | IN | MX | 10 | primary.google.com. |
google.com. | 3600 | IN | MX | 30 | backup.google.com. |
primary.google.com. | 3600 | IN | A | 74.125.28.27 | |
backup.google.com. | 3600 | IN | A | 173.194.211.27 | |
(Similar to NS records, the DNS server may return glue A/AAAA records in addition to the requested MX records.) How long did it take to get the answer?
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