offset these issues.
works are configured with a separate hub for each subnet--even if that
subnet contains as few as two devices. Switches with VLAN capabilities,
with their higher port cost and management systems, may have three or four
subnets connected into the same chassis. In troubleshooting, it is important
to have an accurate understanding of the current switch configuration
and VLAN definitions, and--more importantly--verification that the end
nodes match those definitions. It is not uncommon for a port to be defined
to VLAN 1, where the workstation is configured with an IP address and
default gateway matching VLAN 5. Under such circumstances, the worksta-
tion support staff will believe that the configuration is correct, and the
network administrator will document that the port is correct. In addition to
the show port command, it is important to have valid documentation of all
VLANs and the associated network configurations for each VLAN.
another without a router or routing function. Recall that switches operate at
Layer 2 of the OSI model, and although switches are available with routing
engines and even Layer 4 processors, this section will retain a definition
limited to Layer 2.
tor with a cost-effective option in deploying switches and VLANs in the net-
work. For example, a normal switch installation requires a single port in
each VLAN to be connected to the corresponding router interface, assuming
a typical installation in which each VLAN is a logical extension of a subnet.
This requires N ports on the router, in addition to the same number of ports
on the switch.
costs and fails to account for differences in local and remote traffic. Recall
that networks were historically designed with 80 percent of the traffic
remaining on the local subnet. Although the percentage of local traffic is
significantly lower today, you would still be unlikely to find all traffic leaving
the subnet.