Solution to CSE 489/589Homework Assignment 3
Prepared by Hung Q. Ngo
*
Problem 1.
Consider the graph in Figure 1. Assume the routing tables contain only two fields: the
destination and the next node router. Using
Dijkstra’s algorithm
, compute the routing table at
node F
.
Show work by using the table of iterations of the algorithm as we did in class. No points will be given if
you only give the final shortest path tree and/or the routing table.
Figure 1: Network of routers for this question
Iteration
The Set T
Node A
Node B
Node C
Node D
Node E
Node F
0
∅
Nil,
∞
Nil,
∞
Nil,
∞
Nil,
∞
Nil,
∞
Nil,
0
1
F
F, 2
F,3
2
F,A
A,12
A,4
3
F,A,D
D,6
D,11
4
F,A,D,E
E,10
5
F,A,D,E,B
B,9
6
F,A,D,E,B,C
Draw your tree here
Your routing table for node F here
Two branches: F–D–B–C, F–A–E
Destination
Next Router
A
A
B
D
C
D
D
D
E
A
*
Please let me know of any mistake/typo ASAP.
1
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Problem 2.
Consider the network in Figure 2. Suppose the routing tables’s entries for
destination
F
Figure 2: Network of routers for this question
at time
0
are shown below. Also assume that all routers are perfectly synchronized so that they all send
updates at the same time slot. (The table below shows the table states at time
0
.) Compute the routing
table entries for destination
F
as the Distance Vector protocol is run over time, until no further changes
are possible for any table.
Time
entry at
F
entry at
A
entry at
B
entry at
C
entry at
D
entry at
E
0
(
0
, NULL)
(
∞
, NULL)
(
∞
, NULL)
(
∞
, NULL)
(
∞
, NULL)
(
∞
, NULL)
1
3, F
1, F
2
2, B
5, A
9, A
3
4, A
7, C
10, D
4
6, C
8, D
5
7, D
6
7
8
9
10
The semantic of an entry is: (cost, nexthop). (The table might have more rows than needed.)
Problem 3.
(a) Consider a subnet with prefix 202.84.208/21, give an example of one IP address (of
the form xxx.xxx.xxx.xxx) that can be assigned to this network
(b) Suppose an ISP owns a block of addresses of the form 202.84.208/21, and suppose it wants to
create
4
equalsized subnets from this block, what are the prefixes (of the form a.b.c.d/x) for the
four subnets?
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 Fall '10
 hungngo
 Networking, IP address, Shortest path problem, Classless InterDomain Routing, ASes

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