Deploying Technology in the Campus Infrastructure Module
Issues in a poorly designed network

A poorly designed network has increased support costs, reduced service availability and limited support for new applications and solutions. Less than optimal performance will effect end-users directly as well as effect access to central resources. 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 minimize how far reaching a network problem is when it occurs. When Layer 2 and Layer 3 boundaries are not clearly defined, failure in one network area can have a far-reaching effect.
  • Broadcast domains – Broadcasts exist in every network. Many applications and many network operations require broadcasts to function properly, therefore, it is not possible to completely eliminate broadcasts. Just as with failure domains, in order to minimize the negative impact of broadcasts, broadcast domains should have clear boundaries and include an optimal number of devices.
  • Large amount of unknown MAC unicast traffic – Catalyst switches limit unicast frame forwarding to ports associated with the specific unicast address. However, frames arriving for a destination MAC address not recorded in the MAC table are flooded out all switch ports and this is known as an "unknown MAC unicast flooding." Because this causes excessive traffic on switch ports, NICs have to attend to a larger number of frames on the wire and security can be compromised as data is being propagated on a wire for which is was not intended.
  • Multicast traffic on ports where not intended – IP multicast is a technique that allows IP traffic to be propagated from one source to a multicast group identified by a single IP and MAC destination group address pair. Similar to unicast flooding and broadcasting, multicast frames will be flooded out all ports on the same VLAN where they were received. A proper design allows for containment of multicast frames while allowing them to be functional.
  • Difficulty in management and support – Because a poorly designed network may be disorganized, be poorly documented and be lacking easily identified traffic flows, the support, the maintenance, and the problem resolution become time consuming and arduous tasks.
  • Possible security vulnerabilities – A poorly designed switched network with little thought to security requirements at the access layer can compromise the integrity of the entire network.

A poorly designed network always has a negative impact and becomes a burden for any organization in terms of support and related costs.