computer network assignment

CSCE 416 Introductions to Computer Networks

Take home quiz #3, due April 8, 2010

(10 points in total and only a subset of questions will be graded)

[1]. Consider the following network. With the indicated link costs, use Dijkstra’s shortest-path algorithm to compute the shortest path from x to all network nodes.

a. Show how the algorithm works step by step by filling in the following table. D(y) is the current value of path cost from x to y; p(t) is the predecessor node along path from x to y; N’ is the set of notes whose least path cost has been determined.

b. Draw the shortest-path tree rooted at x.

Step
   

N’
   

D(y),p(y)
   

D(z),p(z)
   

D(u),p(u)
   

D(v),p(v)
   

D(w),p(w)
                       
                       
  [2] Routing and forwarding are the two most important network-layer functions in a datagram network. Answer following questions related to network-layer functions.

a. Do routers have IP addresses? If so, how many?

b. What is the difference between routing and forwarding?

c. Can routing and forwarding both change the forwarding table?

d. Do routers in virtual-circuit network use forwarding tables? If so, how many fields are required for each routing entry?
[3] Suppose A, B, C, D, X, Y, and Z are ASs. X, Y, and Z are ISPs. Suppose that Y and Z are peers (e.g. they will not carry traffic for each other’s customers but their own), and X is a customer of both Y and Z. Suppose A and B are customers of ISP X; C is customer of ISP Y and ISP Z, and D is customer of ISP Z. Suppose that X would like to have the traffic destined to A to come from Y ONLY, and the traffic destined to B come from ISP Z ONLY.

a. How should X advertise its routs to ISP Y and ISP Z?

b. Should Z advertise path BXZ to ISP Y? Why ?

c. Based on the information available at X, draw the network topology viewed by X.
[4] Login to the host “eos.cse.sc.edu”, and use the commands /sbin/ifconfig and nslookup to answer the following questions:
a. What is the IP address, network mask, default router of the host ‘eos.cse.sc.edu’?
b. What is the maximum number of hosts possible on the same subnet of eos.cse.sc.edu?
c. What is IP address of its local DNS server? What is the 32-bit binary equivalent of this IP address?
d. Do ‘eos.cse.sc.edu’ and its local DNS server belong to the same subnet?
e. Define the following terms: subset, prefix, and BGP route.
[5] If the datagrams are limited to 1,500 bytes (including header) between Alice’s computer and Bob’s computer; if the IP header is 20 bytes, how many datagrams have to be required to deliver a movie of 20 million bytes?