The following example shows bandwidth-based multicast storm control being enabled at 70 percent on Gigabit Ethernet interface. VLANs behave much like physical Local Area Networks (LANs), but you can group hosts even if they are not physically co-located. If a network segment in the spanning tree fails and a redundant path exists, the spanning-tree algorithm recalculates the spanning-tree topology and activates the standby path. It enables a set of router interfaces to work together to present the appearance of a single virtual router or default gateway to the hosts on a LAN. You can disable this preemptive scheme using the no vrrp preempt command. For more information on VRRP, see the following link: http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipapp_fhrp/configuration/15-mt/fhp-15-mt-book/fhp-vrrp.html. VLANs have the same attributes as physical LANs, but you can group end stations even if they are not physically located on the same LAN segment. For detailed information on VTP, see the following web link: http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3750/software/release/15-0_2_se/configuration/guide/scg3750/swvtp.html. MAC address notifications are generated for dynamic and secure MAC addresses; events are not generated for self addresses, multicast addresses, or other static addresses. All rights reserved. If you click "OK" and continue to use this site, you are acknowledging that you are OK with this. The following example shows how to enable IGMP snooping on a VLAN interface. Device B is configured as the active device for group 2 and standby device for group 1. The switch that has at least one of its ports in the designated role is called the designated switch.Spanning tree forces redundant data paths into a standby (blocked) state. For configuration examples, see “Example: Configuring MAC Address Notification Traps”. Spanning-tree operation is transparent to end stations, which cannot detect whether they are connected to a single LAN segment or a switched LAN of multiple segments. The MAC address table contains address information that the switch uses to forward traffic between ports. HSRP uses a priority mechanism to determine which HSRP configured device is to be the default active device. Each VLAN is considered a logical network, and packets destined for stations that do not belong to the VLAN must be forwarded through a router. (config-if)#no shutdown. The STP uses a spanning-tree algorithm to select one switch of a redundantly connected network as the root of the spanning tree. Storm control (or traffic suppression) monitors packets passing from an interface to the switching bus and determines if the packet is unicast, multicast, or broadcast. Except for traffic that is required for the SPAN or RSPAN session, destination ports do not receive or forward traffic. Only traffic that enters or leaves source ports or traffic that enters or leaves source VLANs can be monitored by using SPAN; traffic routed to a source VLAN cannot be monitored. BPDUs contain information about the sending switch and its ports, including switch and MAC addresses, switch priority, port priority, and path cost. The switch creates one entry per VLAN in the IGMP snooping IP multicast forwarding table for each group from which it receives an IGMP join request. For a Layer 2 Ethernet network to function properly, only one active path can exist between any two stations. If a loop occurs, spanning tree uses the port priority when selecting an interface to put in the forwarding state. You must dedicate the destination port for SPAN use. Until the client is authenticated, IEEE 802.1x access control allows only Extensible Authentication Protocol over LAN (EAPOL), Cisco Discovery Protocol (CDP), and Spanning Tree Protocol (STP) traffic through the port to which the client is connected. Lastly, we want to bring this port (interface) up or enable it. Spanning tree uses this information to elect the root switch and root port for the switched network and the root port and designated port for each switched segment. HSRP routes IP traffic without relying on the availability of any single router. To configure and assign a switch access port to a VLAN, open a console connection to the switch and run the following IOS commands from interface configuration mode. SPAN copies (or mirrors) traffic received or sent (or both) on source ports or source VLANs to a destination port for analysis. When two ports on a switch are part of a loop, the spanning-tree port priority and path cost settings control which port is put in the forwarding state and which is put in the blocking state.