Quiz 3
COSC650 Computer Networks
Fall 2009
(This exam is open-book, open note exam.)
Name ______________________
1.(3 points) The IPv4 header allocates only _13__ bits to the Offset field, but a packet’s
length can be up to __216 - 1_. In order to support fragmentation of maximum-sized
packet, we must count offsets in multiples of __8_______bytes.
2.(5 points) Consider the fragments of Figure 4.5(b)in pp. 242 all pass through another
router onto a link with an MTU of 380 bytes, not counting the link header. Complete the
fragments information below.
M-bit
_1__
_1__
_1__
_1_
_1__
_0_
1st original fragment
1st original fragment
2nd original fragment
2nd original fragment
3rd original fragment_
3rd original fragment
offset
___0___
___360_
___512_
___872_
__1024_
__1384_
bytes data
___360____
___152____
___360____
___152____
___360____
____16____
3. (12 points) Consider the network below.
A
3
8
D
C
6
F
2
B
1
2
E
Give a global distance-vector tables step-by-step when
a) each node knows only the distances to its immediate neighbors.
At Node
Distance to Reach Node
A
B
C
D
E
F
A
B
C
D
E
F
0
∞
3
8
∞
∞
∞
0
∞
∞
2
∞
3
∞
0
∞
1
6
8
∞
∞
0
2
∞
∞
2
1
2
0
∞
∞
∞
6
∞
∞
0
b) each node has reported the information it had in the preceding step to its immediate
neighbors
At Node
A
B
C
D
E
F
A
B
Distance to Reach Node
C
D
E
F
0
∞
3
8
4
9
∞
0
3
4
2
∞
3
3
0
3
1
6
8
4
3
0
2
∞
4
2
1
2
0
7
9
∞
6
∞
7
0
c) Step (b) happens a second time.
At Node
A
B
C
D
E
F
A
B
Distance to Reach Node
C
D
E
F
0
6
3
6
4
9
6
0
3
4
2
9
3
3
0
3
1
6
6
4
3
0
2
9
4
2
1
2
0
7
9
9
6
9
7
0
d) show how the link-state algorithm builds the routing table for node D.
e) Suppose that the C-E link fails. C and E have reported the news. Then, give the tables
of A and D after their next mutual exchange.
A:
dest cost nexthop
D:
dest cost nexthop
B
12
D
A
8
A
C
3
C
B
4
E
D
8
D
C 11
A
E
10
D
E
2
E
F
9
C
F 17
A
4. (10 poinst) An organization has a class C network 200.1.1 and wants to form subnets
for four departments, with hosts as follow:
A: 72 host,
B: 35 hosts
There are 145 hosts in all.
C: 20 hosts
D: 18 hosts
a) Give a possible arrangement of subnet masks to make this possible and give the full IP
address range for each depart hosts.
Dept
Subnet mask
A
0/
B
10/
C
110/
D
111/
Range of IP full addresses of the dept.
b) Suggest what the organization might do if department D grows to 34 hosts.
A
B
C
D
01/
001/
10/
000/
11/