VLANs
A VLAN is a collection of end nodes grouped by logic rather than physical location. End nodes that frequently communicate with each other are assigned to the same VLAN, regardless of where they are located physically on the network. Logically, a VLAN can be equated to a broadcast domain, because broadcast packets are forwarded only to members of the VLAN on which the broadcast was initiated.
Notes About VLANs on the
1.The
2.The switch’s default - in both Layer 2 Only mode and IP Routing mode - is to assign all ports to a single 802.1Q VLAN named DEFAULT_VLAN.
3.The switch allows the assignment of an IP interface to each VLAN, in IP Routing mode. The VLANs must be configured before setting up the IP interfaces
4.A VLAN that is not assigned an IP interface will behave as a layer 2 VLAN – and IP routing, by the switch, will not be possible to this VLAN regardless of the switch’s operating mode.
IEEE 802.1Q VLANs
Some relevant terms:
Tagging - The act of putting 802.1Q VLAN information into the header of a packet.
Untagging - The act of stripping 802.1Q VLAN information out of the packet header.
Ingress port - A port on a switch where packets are flowing into the switch and VLAN decisions must be made.
Egress port - A port on a switch where packets are flowing out of the switch, either to another switch or to an end station, and tagging decisions must be made.
IEEE 802.1Q (tagged) VLANs are implemented on the
Any port can be configured as either tagging or untagging. The untagging feature of IEEE 802.1Q VLANs allow VLANs to work with legacy switches that don’t recognize VLAN tags in packet headers. The tagging feature allows VLANs to span multiple
802.1Q VLAN Packet Forwarding
Packet forwarding decisions are made based upon the following three types of rules:
•Ingress rules – rules relevant to the classification of received frames belonging to a VLAN.
•Forwarding rules between ports – decides filter or forward the packet
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