Question

Consult the diagram below. There are two DNS servers, a web server (HTTP) and a client laptop. The client wishes to open a web page on the server. The HTTP connection and any required DNS queries are all made over TCP. Here are the round-trip times for the paths shown in the diagram: RTT0 = 7 msecs. RTT1 = 30 msecs. RTTHTTP = 43 msecs. a. Assume the client requests a single object from the web server, but does not have the server's IP address cached, and consults the local DNS cache. If the local DNS cache contains the entry, then what is the total elapsed time to retrieve the first object? ms b. If the DNS entry exists only in the second DNS server, what is the total elapsed time to retrieve the first object? ms c. Assume the first connection included a "Keep Alive" (a.k.a. persistent connection) request which was granted. Now a second object is requested. How long does it take? ms d. Assume DNS entries have 60-minute TTL (time to live) values. 50 minutes after learning the DNS entry for the server, our client has rebooted and cleared everything out of cache, and reopens the same web page as before, requiring the DNS entry again. After supply the DNS record, how much time does the DNS entry have to live? min

          Consult the diagram below. There are two DNS servers, a web server (HTTP) and a client laptop. The client wishes to open a web page on the server. The HTTP connection and any required DNS queries are all made over TCP. Here are the round-trip times for the paths shown in the diagram:
RTT<sub>0</sub> = 7 msecs.
RTT<sub>1</sub> = 30 msecs.
RTT<sub>HTTP</sub> = 43 msecs.
a. Assume the client requests a single object from the web server, but does not have the server's IP address cached, and consults the local DNS cache. If the local DNS cache contains the entry, then what is the total elapsed time to retrieve the first object?
ms
b. If the DNS entry exists only in the second DNS server, what is the total elapsed time to retrieve the first object?
ms
c. Assume the first connection included a "Keep Alive" (a.k.a. persistent connection) request which was granted. Now a second object is requested. How long does it take?
ms
d. Assume DNS entries have 60-minute TTL (time to live) values. 50 minutes after learning the DNS entry for the server, our client has rebooted and cleared everything out of cache, and reopens the same web page as before, requiring the DNS entry again. After supply the DNS record, how much time does the DNS entry have to live?
min

Consult the diagram below. There are two DNS servers, a web server (HTTP) and a client laptop. The client wishes to open a web page on the server. The HTTP connection and any required DNS queries are all made over TCP. Here are the round-trip times for the paths shown in the diagram:
RTT<sub>0</sub> = 7 msecs.
RTT<sub>1</sub> = 30 msecs.
RTT<sub>HTTP</sub> = 43 msecs.
a. Assume the client requests a single object from the web server, but does not have the server's IP address cached, and consults the local DNS cache. If the local DNS cache contains the entry, then what is the total elapsed time to retrieve the first object?
ms
b. If the DNS entry exists only in the second DNS server, what is the total elapsed time to retrieve the first object?
ms
c. Assume the first connection included a "Keep Alive" (a.k.a. persistent connection) request which was granted. Now a second object is requested. How long does it take?
ms
d. Assume DNS entries have 60-minute TTL (time to live) values. 50 minutes after learning the DNS entry for the server, our client has rebooted and cleared everything out of cache, and reopens the same web page as before, requiring the DNS entry again. After supply the DNS record, how much time does the DNS entry have to live?
min

Added by Cristina F.

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