ISL Network Cards

ISL Network Cards
It is worth repeating that many network card vendors nowadays make NICs that can understand
ISL and 802.1Q encapsulated packets. When attempting to keep a large percentage of
traffic from straying from the local VLAN, these cards can be very useful. Fitting a server with
an ISL or 802.1Q-aware NIC means that the server can be a member of multiple VLANs and connect
to a switch via a trunk link.
Example scenarios include installing one of these NICs in an e-mail server or a database server.
Anything that a large number of people, across several VLANs, need to access is a candidate
for this type of connection. It often makes more fiscal sense to upgrade a server NIC than to
upgrade an entire router.

VLSM (variable-length subnet masking) is a technique designed to create flexible
subnets and get the most from your available IP address space. It is covered
in detail in Part I of this book.