Question: Suppose there are six routers, two at access layer, two at distribution layer and two at core layer. Establish a network with these six routers and then explain the features of this network and why you propose such a network.
Answer:
The aggregation routers which are high performance routers converges for the internet usage by injecting the default route, default route metric can be different for the internal network to select the appropriate next hop.
Intermediate routers act as the core routers which are connected to uplink campus aggregation routers and downlink campus access routers; could also be connected to local aggregation routers.
Downstream routers act as network access routers for LAN network using different network as gateway.
Fig-1- non-Mesh (one uplink)
In Fig 1,
We can evaluate the current network topology based on
Network Module cost – The entire link interconnections are relatively few, the port quantity required is less, so the cost of connected network module is relatively less,
Network Infra reliability- The network architecture is relatively simple, has certain redundancy, the simple point breakdown will not affect other link capacities, but retransmits delays can increase. Moreover, the total path cost will also increase, so delaying real time service can have certain influence.
Scalability- Since no. of connected ports are less and hence high free port density is available for extensibility and scalability purpose.
Management and maintenance-The network architecture is relatively simple, once network has the breakdown, the difficulty of trouble shooting is quite low, troubleshooting speed is high, thereby decreasing the overall maintenance cost.
Routing Flexibility- Cannot implement efficient load balancing between service traffic flows.
Summary: The network topology design simple structure, low port density requirements, easy to manage, but also has network redundancy.
Fig-2 – Mesh Topology (Dual uplink)
If we consider 2nd model ,
Network Module cost – The entire link interconnection is relatively high, the port quantity required is high, so the cost of connected network module relatively is also on the high scale.
The network architecture is complex, has very high redundancy due to mesh network, the simple point breakdown will not affect other link capacities, neither retransmits delays can increase. So real time sensitive traffic is not affected in such topologies.
Scalability- Since no of connected ports are high and hence less free port density is available for extensibility and scalability purpose, hence such type of topology is less scalable than non-mesh topology.
Maintenance-The network architecture is relatively complex, once network has the breakdown, the difficulty of trouble shooting is quite high, troubleshooting speed is low, thereby increasing the overall maintenance cost.
Routing Flexibility- Can implement efficient load balancing between service traffic flows.
Summary- This complex network topology design, high port density requirements, is not easy to manage, cost is slightly higher, but better redundancy at the same time.
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