Solutions to End of Chapter Problems
Problem 1:
The change is highlighted below.
IP
MAC
192.168.14.8
192.168.14.9
192.168.14.10
192.168.14.12
192.168.14.13
192.168.14.21
192.168.14.25
AA:BB:CC:DD:EE:FF
AA:BB:AA:BB:AA:BB
A4:B5:C6:D7:E8:F9
EE:FF: EE:FF:EE:FF
A4:B5:C6:D7:E8:F9
C6:D7:C6:D7:C6:D7
E8:F9: E8:F9:E8:F9
Problem 2:
Because when a request is made, the sender does not know the destination's hardware address
yet. This destination hardware address of all 0s is part of the ARP request packet. It should not
be confused with the datalink layer Ethernet frame which has a destination hardware address of
all fs (broadcast address).
Problem 3:
The frame uses a broadcast address so that the intended recipient on the network will receive the
frame even though the sender does not know the specific hardware address of the intended
recipient.
Problem 4:
The first two blocks can be combined into 18.45.24.0/25. This can be seen by looking at the last
octet in each block:
00|000000
01|000000
and noting that if these blocks are to be combined, the second bit in the last block doesn't matter
(i.e., whether it is a 0 or a 1, it will be included).
So our task is now to combine:
and
18.45.24.0/25
18.45.24.128/25
into a single block.
We look at the last octet for each of these blocks:
0|0000000
1|0000000
and notice that if these blocks are to be combined, the first bit in the last block doesn't matter
(i.e., whether it is a 0 or a 1, it will be included).
So, the combined block is 18.45.24.0/24
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Problem 5:
Mask
/30
/29
/27
/0
Problem 6:
Network address/mask
2.2.2.4
4.4.4.40
3.3.3.32
0.0.0.0
Next-hop address
------------default router
Interface
m0
m1
m2
(none given in
this problem)
It first applies the mask /30 to the incoming address and obtains 3.3.3.36 which does not match
the corresponding network mask
The router then goes to the next line of the routing table, and applies the mask /29 to the
incoming address, obtaining 3.3.3.32. This does not match the corresponding network mask.
The router then goes to the next line of the routing table, and applies the mask /27 to the
incoming address, obtaining 3.3.3.32. This does match the corresponding network mask.
The packet is routed out on interface m2.
Problem 7:
An ARP reply may be trusted/accepted in the absence of a preceding ARP request.
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