Cabletron Systems SmartSTACK ELS10-27MDU User Manual Addendum

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VLANs on the ELS10-27MDU49033276VLANs on the ELS10-27MDUIEEE 802.1Q is a standard for virtual bridged local area networks(VLANs). It provides an alternate method for forwarding packets througha switch. In an 802.1D (Spanning Tree) bridge, packets are forwarded inaccordance with the spanning tree as dynamically created by the 802.1Dprotocol Bridge Protocol Data Units (BPDUs), and the spanning tree stateof each port. In 802.1Q, in addition to spanning tree, packets areforwarded 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 foringress (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 packetsand the decision to either drop them, or forward them to the forwardingprocess.The forwarding rules deal with forwarding packets utilizing topologyrestrictions, the filtering database, queue frames (not supported), mappriorities (not supported), and recalculation of the FCS. The forward/filtering database can contain three types of entries:• Permanent entries• Static entries• Dynamic entriesDynamic entries are created by the protocols supported by the switch(GVRP). There will be no learning of VLANs outside of this protocol.The egress rules deal with whether the destination port(s) are members ofthe VLAN, and whether the VLAN tag is to be stripped.802.1Q does NOT replace 802.1D, but limits the relaying of packets on thespanning tree to a subset. The subset being the members of a particularVLAN. This is determined by comparing the VLAN ID, which is heldwithin the tag, to the ports which are members of that VLAN. Themaximum number of VLANs supported in 802.1Q is 32.