Configuring Virtual LANs (VLANs)
December 2005 © Foundry Networks, Inc. 11 - 11
Dynamic Ports
Dynamic ports are added to a VLAN when you create the VLAN. However, if a dynamically added port does not
receive any traffic for the VLAN’s protocol within ten minutes, the port is removed from the VLAN. However, the
port remains a candidate for port membership. Thus, if the port receives traffic for the VLAN’s protocol, the device
adds the port back to the VLAN.
After the port is added back to the VLAN, the port can remain an active member of the VLAN up to 20 minutes
without receiving traffic for the VLAN’s protocol. If the port ages out, it remains a candidate for VLAN membership
and is added back to the VLAN when the VLAN receives protocol traffic. At this point, the port can remain in the
VLAN up to 20 minutes without receiving traffic for the VLAN’s protocol, and so on.
Unless you explicitly add a port statically or exclude a port, the port is a dynamic port and thus can be an active
member of the VLAN, depending on the traffic it receives.
NOTE: You cannot configure dynamic ports in an AppleTalk cable VLAN. The ports in an AppleTalk cable VLAN
must be static. However, ports in an AppleTalk protocol VLAN can be dynamic or static.
Figure 11.7 shows an example of a VLAN with dynamic ports. Dynamic ports not only join and leave the VLAN
according to traffic, but also allow some broadcast packets of the specific protocol to “leak” through the VLAN.
See “Broadcast Leaks” on page 11-12.
Figure 11.7 VLAN with dynamic ports—all ports are active when you create the VLAN
C = candidate port
A = active port
When you add ports dynamically,
all the ports are added when you add
the VLAN.
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