Brocade FastIron Ethernet Switch Platform and Layer 2 Switching Configuration Guide - Manual (Page 347)

• If the port belongs to an IP subnet VLAN, IPX network VLAN, or AppleTalk cable VLAN and the
packet belongs to the corresponding IP subnet, IPX network, or AppleTalk cable range, the device
forwards the packet to all the ports within that VLAN.
• If the packet is a Layer 3 packet but cannot be forwarded as described above, but the port is a
member of a Layer 3 protocol VLAN for the packet protocol, the device forwards the packet on all the
Layer 3 protocol VLAN ports.
• If the packet cannot be forwarded based on either of the VLAN membership types listed above, but
the packet can be forwarded at Layer 2, the device forwards the packet on all the ports within the
receiving port port-based VLAN.
Protocol VLANs differ from IP subnet, IPX network, and AppleTalk VLANs in an important way. Protocol
VLANs accept any broadcast of the specified protocol type. An IP subnet, IPX network, or AppleTalk
VLAN accepts only broadcasts for the specified IP subnet, IPX network, or AppleTalk cable range.
NOTE
Protocol VLANs are different from IP subnet, IPX network, and AppleTalk cable VLANs. A port-based
VLAN cannot contain both an IP subnet, IPX network, or AppleTalk cable VLAN and a protocol VLAN
for the same protocol. For example, a port-based VLAN cannot contain both an IP protocol VLAN and
an IP subnet VLAN.
Layer 2 port-based VLANs
On all Brocade devices, you can configure port-based VLANs. A port-based VLAN is a subset of ports
on a Brocade device that constitutes a Layer 2 broadcast domain.
By default, all the ports on a Brocade device are members of the default VLAN. Thus, all the ports on
the device constitute a single Layer 2 broadcast domain. When you configure a port-based VLAN, the
device automatically removes the ports you add to the VLAN from the default VLAN.
You can configure multiple port-based VLANs. You can configure up to 4094 port-based VLANs on a
Layer 2 Switch or Layer 3 Switch. On both device types, valid VLAN IDs are 1 - 4095. You can
configure up to the maximum number of VLANs within that ID range.
NOTE
VLAN IDs 4087, 4090, and 4093 are reserved for Brocade internal use only. VLAN 4094 is reserved for
use by Single STP. Also, if you are running an earlier release, VLAN IDs 4091 and 4092 may be
reserved for Brocade internal use only. If you want to use VLANs 4091 and 4092 as configurable
VLANs, you can assign them to different VLAN IDs. For more information, refer to
Assigning different
VLAN IDs to reserved VLANs 4091 and 4092 on page 373
NOTE
Each port-based VLAN can contain either tagged or untagged ports. A port cannot be a member of
more than one port-based VLAN unless the port is tagged. 802.1Q tagging allows the port to add a four-
byte tag field, which contains the VLAN ID, to each packet sent on the port. You also can configure port-
based VLANs that span multiple devices by tagging the ports within the VLAN. The tag enables each
device that receives the packet to determine the VLAN the packet belongs to. 802.1Q tagging applies
only to Layer 2 VLANs, not to Layer 3 VLANs.
Because each port-based VLAN is a separate Layer 2 broadcast domain, by default each VLAN runs a
separate instance of the Spanning Tree Protocol (STP).
Layer 2 traffic is bridged within a port-based VLAN and Layer 2 broadcasts are sent to all the ports
within the VLAN.
Layer 2 port-based VLANs
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