Exam: Cisco 200-301 - Cisco Certified Network Associate (CCNA)
As discussed in the previous objective that it is always better to break a big network into small network segments to enhance the performance of the network. A network can be broken into small network segments with the use of network devices such as hubs, switches, bridges and routers. Let us understand when to use which network component to meet a network specification.
Before finalizing your network devices, you need to consider the following requirements of your network:
Manage broadcast traffic
It is important to figure out your broadcast traffic because a large broadcast domain deteriorates the performance of a network. Each host on a network need not receives all the broadcasts. Therefore a network must be divided into small network domains so that all the broadcasts are not received by all the hosts on a network. Only routers can break the broadcast domains, so you need routers to break broadcast domains.
Manage network collisions
Network collisions occur when network data packets collide with each other. Collisions deteriorate the network performance. Therefore, it is important to manage collisions in a network. The bridges and switches break the collision domains but do not break the broadcast domains. So to increase the performance of a network a broadcast domain must be broken down further into multiple collision domains.
The hubs can only be used to connect network devices they can neither be used to break broadcast domains nor collision domains. So, if you use only hubs in your network then the performance of your network will deteriorate with the increase in network size
Group similar users together
A network should be broken into smaller networks on the basis of similarity of requirements of the network users.For example, the users who need to file servers excessively must be put together in the same network segment.
Manage hop count
A network with less hops (jumping from one device to another) is always better in performance as compared to a network that has too many hops. The hop counts can be reduced in a network by connecting the servers to the routers. A port on a router can be connected to an 8 port switch or a layer 3 switch to connect servers to routers. The servers directly connecting to routing devices ensure fewer hops and allow the traffic to directly move from clients to servers.
Manage network failure
You can connect a router to switches and then connect switches to host computers instead of chaining all the hosts together. Another advantage of switches is that switches spread the traffic to multiple connections and in case of a connection failure the other connections would keep working if connected with each other through cables.
A Small Office Network Arrangement Example
The best network arrangement is one that meets all your company requirements and that has all networking devices connected with each other in a perfect manner.
To practically understand the use of networking devices in a given situation, let us create a small office network with three departments IT, HR, R&D separated into network segments by a router. Each segment internally uses a different network device for the purpose of understanding their usage implications. The details of each network segment are as follows:
The network design presented here creates three segments with the use of router. The first segment created for the IT department uses switches. We know that each port on the switch creates a separate collision domain but the same broadcast domain. This means that all the computers on the segment will have to listen to all the broadcasts transmitted to the segment, which means the segment has to process a large number of broadcasts, which can cause low bandwidth and high response time for the network. As the number of computers increase in the segment the performance of the segment will deteriorate.
This design is better than the other two designs because the switches placed at the centre of the subnet creates virtual LAN (VLAN), which can manage the broadcast traffic by sending each broadcast to its relevant VLAN only. Segmenting large network into smaller VLANS is cheaper than segmenting your network through routers. The VLANS still require routers for interconnectivity between network segments.
The second segment, the HR department uses a bridge that connects to hubs inside the segment. This network segment arrangement again creates one broadcast domain with two collision domains created by the bridge. However the each hub connected to the bridge creates one separate collision domain for each device connected to it. The two collision domains created by this network arrangement is still better than only one collision domain, which is the scenario in the R&D department. The network arrangement in this segment is inferior to IT department segment. The one broadcast domain and two collision domains will decrease the performance of the network
The third segment created for the R&D department uses only hubs, which creates one broadcast domain and one collision domain. The performance of this network segment will be worse of the other two networking segments created on the network.
Example Question:
How many collision domains and broadcast domains are depicted in the Figure above?
Answer: B
The network shows three broadcast domains, which can be clearly identified by the router, which break broadcast domains by default.
The network shows 11 collision domains. One collision domain for R&D department that uses only hubs, three collision domains for the HR department that uses bridge, and seven collision domains for the IT department that usesswitches.
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