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.Use the no form of this command to resume normal forwarding.port block {unicast | multicast}no port block {unicast | multicast}Syntax Description unicast Packets with unknown unicast addresses are not forwarded to this port.multicast Packets with unknown multicast addresses are not forwarded to this port.Defaults Flood unknown unicast and multicast packets to all ports.Command Modes Interface configurationCommand History Release Modification11.2(8)SA This command was first introduced.Usage Guidelines The port block command cannot be entered for a network port.If a trunk port is not a network port, the unicast keyword applies.The multicast keyword is supportedon trunk ports.Both port block features affect all the VLANs associated with the trunk port.Examples This example shows how to block the forwarding of multicast and unicast packets to a port:Switch(config-if)# port block unicastSwitch(config-if)# port block multicastYou can verify the previous commands by entering the show port block user EXEC command.Related Commands Command Descriptionshow port block Displays the blocking of unicast or multicast flooding to a port.Catalyst 2900 Series XL and Catalyst 3500 Series XL Command Reference78-12155-042-82 Chapter 2 Cisco IOS Commandsport groupport groupUse the port group interface configuration command to assign a port to a Fast EtherChannel or GigabitEtherChannel port group.Up to 12 port groups can be created on a switch.Any number of ports canbelong to a destination-based port group.Up to eight ports can belong to a source-based port group.Usethe no form of this command to remove a port from a port group.port group group-number [distribution {source | destination}]no port groupSyntax Description group-number Port group number to which the port belongs.The range isfrom 1 to 12.distribution {source | destination} (Optional) Forwarding method for the port group." source Set the port to forward traffic to a port groupbased on the packet source address.This is the defaultforwarding method." destination Set the port to forward traffic to a portgroup based on the packet destination address.Defaults Port does not belong to a port group.The default forwarding method is source.Command Modes Interface configurationCommand History Release Modification11.2(8)SA3 This command was first introduced.Usage Guidelines An Asynchronous Transfer Mode (ATM) port is the only port that cannot belong to a port group.For allother ports, these restrictions apply:" Do not group Fast Ethernet and Gigabit ports together." No port group member can be configured for Switched Port Analyzer (SPAN) port monitoring." No port group member can be enabled for port security." You can create up to 12 port groups.You can have source-based port groups and destination-basedsource groups.A source-based port group can have up to eight ports in its group.Adestination-based port group can contain an unlimited number of ports in its group.You cannot mixsource-based and destination-based ports in the same group.You can independently configure portgroups that link switches, but you must consistently configure both ends of a port group.Catalyst 2900 Series XL and Catalyst 3500 Series XL Command Reference78-12155-042-83 Chapter 2 Cisco IOS Commandsport group" Port group members must belong to the same set of VLANs and must be all static-access, allmulti-VLAN, or all trunk ports." Dynamic-access ports cannot be grouped with any other port, not even with other dynamic-accessports.When a group is first formed, the switch automatically sets these parameters to be the same on all ports:" VLAN membership of ports in the group" VLAN mode (static, multi, trunk) of ports in the group" Encapsulation method of the trunk" Native VLAN configuration if the trunk uses IEEE 802.1Q" Allowed VLAN list configuration of the trunk port" Spanning Tree Protocol (STP) Port Fast option" STP port priority" STP path cost" Network port configuration for source-based port group" Protected portConfiguration of the first port added to the group is used when setting the above parameters for otherports in the group.After a group is formed, changing any parameter in the above list changes theparameter on all other ports.Use the distribution keyword to customize the port group to your particular environment.Theforwarding method you choose depends on how your network is configured.However, source-basedforwarding works best for most network configurations.This command is not supported on the ATM modules.Examples This example shows how to add a port to a port group by using the default source-based forwarding:Switch(config-if)# port group 1This example shows how to add a port to a group by using destination-based forwarding:Switch(config-if)# port group 2 distribution destinationYou can verify the previous commands by entering the show port group user EXEC command.Related Commands Command Descriptionshow port group Displays the ports that belong to a port group.Catalyst 2900 Series XL and Catalyst 3500 Series XL Command Reference78-12155-042-84 Chapter 2 Cisco IOS Commandsport monitorport monitorUse the port monitor interface configuration command to enable Switch Port Analyzer (SPAN) portmonitoring on a port.Use the no form of this command to return the port to its default value.port monitor [interface | vlan vlan-id]no port monitor [interface | vlan vlan-id]Syntax Description interface (Optional) Module type, slot, and port number for the SPAN to be enabled.The interface specified is the port to be monitored.vlan vlan-id (Optional) ID of the VLAN to be monitored.Note VLAN 1 is the only valid option.Defaults Port does not monitor any other ports.Command Modes Interface configurationCommand History Release Modification11.2(8)SA This command was first introduced.11.2(8)SA3 The vlan keyword was added.Usage Guidelines Enabling port monitoring without specifying a port causes all other ports in the same VLAN to bemonitored.Entering the port monitor vlan 1 command causes monitoring of all traffic to and from the IP addressconfigured on VLAN 1.Asynchronous Transfer Mode (ATM) ports are the only ports that cannot be monitor ports.However,you can monitor ATM ports.These restrictions apply for ports that have port-monitoring capability:" A monitor port cannot be in a Fast EtherChannel or Gigabit EtherChannel port group." A monitor port cannot be enabled for port security." A monitor port cannot be a multi-VLAN port." A monitor port must be a member of the same VLAN as the port monitored.VLAN membershipchanges are not allowed on monitor ports and ports being monitored
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