Best Practices
VLAN networks need many of the same considerations that normal Ethernet
lines demand. For instance, VLANs should have one IP subnet. By supplying
consecutive subnets to VLANs, the routing advertisements can be summarized
(which has many benefits to convergence).
A stereotypical description of capacity requirements is possible. Access ports
are assigned to a single VLAN and should be Fast Ethernet or faster. Ports to
the distribution layer should be Gigabit Ethernet or better. Core ports are
Gigabit Etherchannel or 10-Gig Ethernet. Remember that uplink ports need
to be able to handle all hosts communicating concurrently, and remember
that although VLANs logically separate traffic, traffic in different VLANs
can still experience contention with other VLANs when both VLANs travel
over the same trunk line.
Take into account the entire traffic pattern of applications found in your
network. For instance, Voice VLANs pass traffic to a remote Call Manager.
Multicast traffic has to communicate back to the routing process and possibly
call upon a Rendezvous Point.