Enterasys els10-27mdu 用户指南
VLANs on the ELS10-27MDU
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VLANs on the ELS10-27MDU
IEEE 802.1Q is a standard for virtual bridged local area networks
(VLANs). It provides an alternate method for forwarding packets through
a switch. In an 802.1D (Spanning Tree) bridge, packets are forwarded in
accordance with the spanning tree as dynamically created by the 802.1D
protocol Bridge Protocol Data Units (BPDUs), and the spanning tree state
of each port. In 802.1Q, in addition to spanning tree, packets are
forwarded in accordance with a VLAN tag that is embedded in the packet,
and the set of ports registered for that VLAN. A set of rules is used for
ingress (receipt), forwarding, and egress (transmit).
(VLANs). It provides an alternate method for forwarding packets through
a switch. In an 802.1D (Spanning Tree) bridge, packets are forwarded in
accordance with the spanning tree as dynamically created by the 802.1D
protocol Bridge Protocol Data Units (BPDUs), and the spanning tree state
of each port. In 802.1Q, in addition to spanning tree, packets are
forwarded in accordance with a VLAN tag that is embedded in the packet,
and the set of ports registered for that VLAN. A set of rules is used for
ingress (receipt), forwarding, and egress (transmit).
The ELS10-27MDU provides support for port based VLANs.
The ingress rules deal with the reception of tagged and untagged packets
and the decision to either drop them, or forward them to the forwarding
process.
and the decision to either drop them, or forward them to the forwarding
process.
The forwarding rules deal with forwarding packets utilizing topology
restrictions, the filtering database, queue frames (not supported), map
priorities (not supported), and recalculation of the FCS. The forward/
filtering database can contain three types of entries:
restrictions, the filtering database, queue frames (not supported), map
priorities (not supported), and recalculation of the FCS. The forward/
filtering database can contain three types of entries:
•
Permanent entries
•
Static entries
•
Dynamic entries
Dynamic entries are created by the protocols supported by the switch
(GVRP). There will be no learning of VLANs outside of this protocol.
(GVRP). There will be no learning of VLANs outside of this protocol.
The egress rules deal with whether the destination port(s) are members of
the VLAN, and whether the VLAN tag is to be stripped.
the VLAN, and whether the VLAN tag is to be stripped.
802.1Q does NOT replace 802.1D, but limits the relaying of packets on the
spanning tree to a subset. The subset being the members of a particular
VLAN. This is determined by comparing the VLAN ID, which is held
within the tag, to the ports which are members of that VLAN. The
maximum number of VLANs supported in 802.1Q is 32.
spanning tree to a subset. The subset being the members of a particular
VLAN. This is determined by comparing the VLAN ID, which is held
within the tag, to the ports which are members of that VLAN. The
maximum number of VLANs supported in 802.1Q is 32.