Question 1) Instead of traceroute, you can also use ping to determine the route that packets take to a given network host.
It does so by using IP Record Route option. Try the following two commands:
ping -R www.cmu.edu
traceroute www.cmu.edu
Write down the difference in their output? Now try the following:
ping -R www.google.com
Do you get the desired output? Describe your observation. Finally, try running the following command a few times.
traceroute www.whitehouse.gov
What do you notice about the results you get from different runs?
Question 2) Harry Bovik is working on web site which has multiple replicated servers located throughout the Internet. He plans on using DNS to help direct clients to their nearest server replica. He comes up with the hierarchical scheme. Harry has divided his server replicas into three groups (east, west and central) based on their physical location. A typical query occurs as follows:
When the client makes a query for www.distributed.hb.com, the root and.com name servers are contacted first. It returns name server (NS) record for ns1.hb.com. The TTL of this record is set to 1 day. The ns1.hb.com name server is then queried for the address. It examines source of the name query and returns a NS record for one of {east-ns, central-ns, west-ns} .distributed.com. The choice of which name server is based on where ns1 thinks the query came from. At last, one of {east-ns, central-ns, west-ns}.distributed.com. is contacted and it returns the address (A) record for the most lightly loaded server in its region.
Answer the following questions based on this design.
a) Harry's name server software has only two options for TTL settings for A and NS records - 1 day and 1 minute. Harry selects the following TTLs for each record below:
1. NS record for {east-ns, central-ns, west-ns} distributed.com - 1 day TTL.
2. A record for {east-ns, central-ns, west-ns} .distributed.com- 1 day TTL.
3. A record returned for the actual Web server - 1 minute TTL.
Briefly describe why Harry's choices are reasonable, or why you would have made different choices.
b) In general, name resolution systems map names based on the name and context. In this particular case, what are two items of context that the name resolution uses?
c) Harry's Web site is especially popular among CMU students. The CMU network administrator estimates that there is one access from CMU every 3 minutes. Each access results in the application resolving the name www.distributed.hb.com
Suppose the following:
No other DNS queries are made in CMU
All CMU clients use the same local name server. This local name server is mapped to the east-ns region. Web browsers do not do any caching on their own.
How many accesses per hour will be made to the following name servers to resolve these CMU queries? Describe your calculation.
1. The Root Servers
2. ns1.hb.com
3. east-ns.distributed.com