Foundry Configuration Guide for the FESX, FSX, and FWSX
11 - 12 © Foundry Networks, Inc. December 2005
Ports in a new protocol VLAN that do not receive traffic for the VLAN’s protocol age out after 10 minutes and
become candidate ports. Figure 11.8 shows what happens if a candidate port receives traffic for the VLAN’s
protocol.
Figure 11.8 VLAN with dynamic ports—candidate ports become active again if they receive protocol traffic
Static Ports
Static ports are permanent members of the protocol VLAN. The ports remain active members of the VLAN
regardless of whether the ports receive traffic for the VLAN’s protocol. You must explicitly identify the port as a
static port when you add it to the VLAN. Otherwise, the port is dynamic and is subject to aging out.
Excluded Ports
If you want to prevent a port in a port-based VLAN from ever becoming a member of a protocol, IP sub-net, IPX
network, or AppleTalk cable VLAN configured in the port-based VLAN, you can explicitly exclude the port. You
exclude the port when you configure the protocol, IP sub-net, IPX network, or AppleTalk cable VLAN.
Excluded ports do not leak broadcast packets. See “Broadcast Leaks” on page 11-12.
Broadcast Leaks
A dynamic port becomes a member of a Layer 3 protocol VLAN when traffic from the VLAN's protocol is received
on the port. After this point, the port remains an active member of the protocol VLAN, unless the port does not
receive traffic from the VLAN's protocol for 20 minutes. If the port does not receive traffic for the VLAN's protocol
for 20 minutes, the port ages out and is no longer an active member of the VLAN.
To enable a host that has been silent for awhile to send and receive packets, the dynamic ports that are currently
members of the Layer 3 protocol VLAN "leak" Layer 3 broadcast packets to the ports that have aged out. When a
host connected to one of the aged out ports responds to a leaked broadcast, the port is added to the protocol
VLAN again.
To "leak" Layer 3 broadcast traffic, an active port sends 1/8th of the Layer 3 broadcast traffic to the inactive (aged
out) ports.
Static ports do not age out and do not leak broadcast packets.
Ports that time out remain candidates for
membership in the VLAN and become active
again if they receive traffic for the VLAN’s
protocol, IP sub-net, IPX network, or
AppleTalk cable range.
When a candidate port rejoins a VLAN,
the timeout for that port becomes 20 minutes.
Thus, the port remains an active member of
the VLAN even if it does not receive traffic
for 20 minutes. After that, the port becomes
a candidate port again.
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