Increased support costs
Reduced support for services and solutions
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A poorly designed network has increased support costs, reduced services and solutions that can be supported, and nonoptimal performance issues that most likely will affect end users directly.
Here are some of the issues that stem from a poorly designed network:
■ Failure domains: One of the most important reasons to implement an effective design is to reduce the impact of network problems resulting from s errors in protocol-stack implementations, network configuration, faulty NICs transmitting bad frames or packets, and broadcast-intensive applications. These issues could have an impact on the entire network in a flat or poorly designed switched environment, potentially to the point of a total failure. Failure domains coexist with broadcast domains and can be bound to a single network segment.
■ Broadcast domains: Broadcast domains exist in every network. Many applications and network operations require broadcasts to function properly. Therefore, it is not possible to completely eliminate broadcast domains. However, just as with failure domains, it is crucial to minimize any impact on a network. Broadcasts consume end-user resources and affect bandwidth availability. End-user resources are consumed because every broadcast must be processed to some extent by the end nodes receiving the broadcast, regardless of whether the broadcast was intended for that node. A poorly designed network will propagate broadcasts over a large number of end-user nodes affecting a large portion of a network population.
■ Isolation of unknown MAC unicast floods: Internally, Catalyst switches implement
VLANs by maintaining a MAC table on a per VLAN basis. This limits frame forwarding to ports only in the same VLAN. In the case of unicast traffic, this is limited to only that specific switch port on which the destination device is located. However, if a frame arrives for a destination MAC address that has not been recorded in the MAC table, the switch will perform what is called an "unknown MAC unicast flood." The frame is flooded to all switch ports within the same VLAN in an effort to deliver the frame. A unicast flood also has the same effect as a broadcast in that every end node must receive the frame to determine whether the date is destined for that node. Again, a proper network design limits the impact of such floods with a small, well-defined subset of the network.
Isolation of multicast traffic: IP multicast is a technique that allows IP traffic to be propagated from one source to a number of destinations, or from many sources to many destinations. Rather than sending one packet to each destination, one packet is sent to the multicast group identified by a single IP and MAC destination group address pair. Similar to unicast flooding and broadcasting, multicasts can congest and have a negative impact on a poorly designed network. A proper design allows for multicast functionality without the negative effects.
Ease of management and support: Because a poorly designed network is unorganized and lacks the deterministic features found within the Enterprise Composite Network model, support, maintenance, and problem resolution become extremely time consuming and arduous tasks.
A poorly designed network always has a negative impact and becomes a burden for any organization in terms of support and related costs.
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