Configuring Virtual LANs (VLANs)
December 2000 25 - 13
packets. Only when the port receives eight AppleTalk broadcast packets or eight DECnet broadcast packets does
the port send the eighth packet of that protocol type.
Figure 25.10 shows an example of a Layer 3 IP protocol VLAN with dynamic ports. Since the ports have dynamic
membership, they are “leaky”. They forward every eighth broadcast packet of non-IP protocols. For example,
when the Macintosh computer sends its eighth broadcast packet, the VLAN forwards the packet. In a VLAN with
static ports, the VLAN never forwards broadcast packets of other protocol types.
Figure 25.10 Protocol VLAN with “leaky” (dynamic) ports
Super Aggregated VLANs
You can aggregate multiple VLANs within another VLAN. This feature allows you to construct Layer 2 paths and
channels. This feature is particularly useful for Virtual Private Network (VPN) applications ins which you need to
provide a private, dedicated Ethernet connection for an individual client to transparently reach its sub-net across
multiple networks.
For an application example and configuration information, see “Configuring Super Aggregated VLANs” on
page 25-47.
Trunk Group Ports and VLAN Membership
A trunk group is a set of physical ports that are configured to act as a single physical interface. Each trunk group’s
port configuration is based on the configuration of the lead port, which is the lowest numbered port in the group.
If you add a trunk group’s lead port to a VLAN, all of the ports in the trunk group become members of that VLAN.
IP host
Mac
IP host
This is a Layer 3 IP protocol VLAN.
The ports in the VLAN accept and
forward all IP broadcasts.
The ports also are dynamic, rather
than static. Thus, they also accept
and forward every eighth broadcast
of other protocol types.
When the Macintosh computer sends
its eighth broadcast packet, the VLAN
forwards the packet so the Mac can
find its servers.
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