Understanding Legacy LAN Segment
In a VLAN environment, a user can be situated physically
anywhere in the network, and still be part of a group of users that have the
same requirements such as IP addressing and specific network privileges. In
legacy networks, hosts with similar network requirements had to be on the same
LAN segment. On the other hand, VLANs are logical and not bound to any physical
location.
In legacy networks, users connected to a hub, which may have
been connected to some kind of bridge or router if wide-area connectivity was
required (see Figure 4-1). Multiple hubs
were interconnected to allow more users on the same segment.
This type of network enabled a department with a large number
of users to remain part of the same segment. This setup was easy for a network
engineer to implement, because generally one network configuration was supported
for that department. For example, the department likely had local file servers
on the same Layer 2 segment allowing most, if not all, traffic to stay
local.
Cascading hubs allow more users to be on the same segment at
the cost of causing more contention among hosts trying to access the network. A
bigger collision domain translates to more packet collisions on the network,
and, therefore, more retransmissions and possible packet drops. By cascading
multiple hubs, the possibility of exceeding the cabling requirements of IEEE
802.3 standard exists, which translates to late collisions, causing packet loss.
A defective network interface card (NIC) that "jabbers" can cause severe
performance issues on this type of network because it continuously sends garbled
data, ignoring the carrier sense multiple access collision detect (CSMA/CD) rule
that you learned about in Chapter 1,
"LAN Switching Foundation Technologies."
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