Answers of Exercise 8
1. Describe similarities and differences between a network bridge and Internet router.
Answer:
Similarities: Both connects networks and handles packets
Differences: A bridge connect two LANs and only understand physical and data link protocols.
A router can connect multiple networks in different types and sizes. It understands
physical, data link, network and IP protocols. It is much complex than a bridge.
2. Describe similarities and differences between Internet reference model and ISO 7-layer model.
Answer:
Similarities: Both are layering models, and there are some correspondent relationships between
layers in the two reference models.
Differences: ISO 7-layer model is a model to guide designs and analyses of general networks.
The Internet model is a 5-layer model, specifically used by the Internet protocol
suites. It includes an internet layer which does not exist in ISO model.
3. Identify the address class of the following IP addresses:
a. 200.58.20.165  Class C, network ID: 200.58.20, host ID: 165
b. 128.167.23.20  Class B, network ID: 128.167, host ID: 23.20
c. 127.54.118.21  Class A, loopback address
d. 16.196.128.50  Class A, network ID: 16, host ID: 196.128.50
e. 193.34.121.255  Class C, directed broadcast address
f. 150.156.10.10  Class B, network ID, 150.156, host ID: 10.10
g. 230.10.24.96  Class D, multicast address
Point out which are special addresses. If an address is a host/router IP address in
Class A, B or C, indicate its prefix (network ID) and suffix (host ID).
Answers of Exercise 8
4. A small organization has a Class C address (196.125.56.0) for seven networks each with
24 hosts. Design an appropriate subnet addressing scheme (subnet addresses, host
addresses and mask) for the organization.
Answer: The prefix of 196.125.56 is network ID and cannot be changed. The 8-bits suffix
can be decided by us. We can use the leftmost 3 bits of the 8 bits for identifying 7
subnets and the rightmost 5 bits for identifying hosts:
subnet 1: 196.125.56.0/27,
hosts: 196.125.56.1 ~ 196.125.56.24
subnet 2: 196.125.56.32/27,
hosts: 196.125.56.33 ~ 196.125.56.56
subnet 3: 196.125.56.64/27,
hosts: 196.125.56.65 ~ 196.125.56.88
subnet 4: 196.125.56.96/27,
hosts: 196.125.56.97 ~ 196.125.56.120
subnet 5: 196.125.56.128/27, hosts: 196.125.56.129 ~ 196.125.56.152
subnet 6: 196.125.56.160/27, hosts: 196.125.56.161 ~ 196.125.56.184
subnet 7: 196.125.56.192/27, hosts: 196.125.56.193 ~ 196.125.56.216
Subnet mask: 255.255.255.224
5. Draw a TCP/IP internet that consists of two networks connected by a router. Show two
computers attached to each network. Assign the IP addresses to the four computers and
one router with the assumption that network prefixes or IDs of the two networks are
170.61.192.0/18 and 210.37.136.32/29., respectively.
Answer:
170.61.192.1
210.37.136.33
Network 1
170.61.192.0/18
170.61.192.5
170.61.192.6
Router
Network 2
210.37.136.32/29
210.37.136.34
210.37.136.37