LAN and WAN Topologies 2

Mesh

When downtime is not an option, a mesh topology can be considered. Full-mesh networks
provide a connection to each device from every other device. This solution is often used with
WAN connections.

 

Figure 1.9 – Full-Mesh Topology

Typically, this type of solution will prove very costly. For this reason, partial-mesh topologies
can be considered. This means that there may be one or more “hops,” or routers, to get to each
device.

 

Figure 1.10 – Partial-Mesh Topology

Hub-and-Spoke

Due to the cost of equipment and WAN connections and bandwidth, companies often use a
hub-and-spoke design. A powerful router is in the centre (hub), usually at a company’s HQ,
while the spokes represent remote offices, which require less powerful routers. There are
obviously issues with this type of topology; however, it is still widely used. We will revisit huband-
spoke topologies again in the Frame Relay section, as it still forms a large part of the CCNA
syllabus because of the routing issues it creates. 

 

Figure 1.11 – Hub-and-Spoke Topology 

Physical versus Logical

When you can see the network equipment, you are looking at the physical topology. This can
be misleading because, although the network appears to be wired in a star fashion, it could in
fact be working logically as a ring. A classic example of this is a ring network. Although the
traffic circulates round the ring in a circular fashion, all of the devices plug into a hub. The ring
is actually inside the token ring hub, so you can’t see it from the outside, as illustrated

 

Figure 1.12 – The Ring Is Inside the Hub

You may be asked to identify the different types of networks, both physically and logically. It is
a good idea to remember that the physical topology is what you can see and the logical
topology is what the network can see (i.e., how the data flows). This is summarised in Table 1.1
below