- Index
- Preface
- Product Overview
- Command-Line Interfaces
- Smart Port Macros
- Virtual Switching Systems (VSS)
- Enhanced Fast Software Ugrade (eFSU)
- NSF with SSO Supervisor Engine Redundancy
- RPR Supervisor Engine Redundancy
- Interface Configuration
- UniDirectional Link Detection (UDLD)
- Power Management and Environmental Monitoring
- EnergyWise
- Online Diagnostics
- Onboard Failure Logging
- Switch Fabric Functionality
- Cisco IP Phone Support
- Power over Ethernet
- Layer 2 LAN Ports
- Flex Links
- EtherChannels
- mLACP for Server Access
- IEEE 802.1ak MVRP and MRP
- VLAN Trunking Protocol (VTP)
- VLANs
- Private VLANs (PVLANs)
- Private Hosts
- IEEE 802.1Q Tunneling
- Layer 2 Protocol Tunneling
- STP and MST
- Optional STP Features
- Layer 3 Interface Configuration
- Unidirectional Ethernet (UDE) and unidirectional link routing (UDLR)
- Multiprotocol Label Switching (MPLS)
- L2VPN Advanced VPLS (A-VPLS)
- IP Unicast Layer 3 Switching
- IPv6 Multicast Layer 3 Switching
- MLD Snooping for IPv6 Multicast Traffic
- IPv4 Multicast Layer 3 Switching
- IGMP Snooping and MVR for IPv4 Multicast Traffic
- Configuring MVR for IPv4 Multicast Traffic
- IPv4 IGMP Filtering and Router Guard
- PIM Snooping
- IPv4 Multicast VPN Support
- PFC QoS
- AutoQoS
- MPLS QoS
- PFC QoS Statistics Data Export
- Network Security
- AutoSecure
- Cisco IOS ACL Support
- Cisco TrustSec (CTS)
- Port ACLs (PACLs) and VLAN ACLs (VACLs)
- Denial of Service Protection
- Control Plane Policing (CoPP)
- DHCP Snooping
- IP Source Guard
- Dynamic ARP Inspection
- Traffic Storm Control
- Unknown Unicast and Multicast Flood Control
- Network Admission Control (NAC)
- IEEE 802.1X Port-Based Authentication
- Web-Based Authentication
- Port Security
- NetFlow
- NetFlow Data Export (NDE)
- Call Home
- System Event Archive (SEA)
- Backplane Platform Monitoring
- SPAN, RSPAN, and ERSPAN
- SNMP IfIndex Persistence
- Top-N Reports
- Layer 2 Traceroute Utility
- Mini Protocol Analyzer
- Ethernet Services Line Cards
- Online Diagnostic Tests
- Acronyms
- Understanding Layer 2 Switching
- Default Layer 2 LAN Interface Configuration
- Layer 2 LAN Interface Configuration Guidelines and Restrictions
- Configuring LAN Interfaces for Layer 2 Switching
- Configuring a LAN Port for Layer 2 Switching
- Enabling Out-of-Band MAC Address Table Synchronization
- Configuring MAC Address Table Notification
- Configuring a Layer 2 Switching Port as a Trunk
- Configuring the Layer 2 Switching Port as an ISL or 802.1Q Trunk
- Configuring the Layer 2 Trunk to Use DTP
- Configuring the Layer 2 Trunk Not to Use DTP
- Configuring the Access VLAN
- Configuring the 802.1Q Native VLAN
- Configuring the List of VLANs Allowed on a Trunk
- Configuring the List of Prune-Eligible VLANs
- Completing Trunk Configuration
- Verifying Layer 2 Trunk Configuration
- Configuration and Verification Examples
- Configuring a LAN Interface as a Layer 2 Access Port
- Configuring an IEEE 802.1Q Custom EtherType Field Value
Configuring LAN Ports for Layer 2 Switching
This chapter describes how to use the command-line interface (CLI) to configure Fast Ethernet, Gigabit Ethernet, and 10-Gigabit Ethernet LAN ports for Layer 2 switching in Cisco IOS Release 12.2SX. The configuration tasks in this chapter apply to LAN ports on switching modules and to the LAN ports on the supervisor engine and Cisco ME 6500 Series Ethernet switches.
Note ● For complete syntax and usage information for the commands used in this chapter, see the Cisco IOS Master Command List, at this URL:
http://www.cisco.com/en/US/docs/ios/mcl/allreleasemcl/all_book.html
- To configure Layer 3 interfaces, see Chapter30, “Configuring Layer 3 Interfaces”
Understanding Layer 2 Switching
These sections describe how Layer 2 switching works in Cisco IOS Release 12.2SX:
Understanding Layer 2 Ethernet Switching
Layer 2 Ethernet Switching Overview
Layer 2 Ethernet ports on Cisco switches support simultaneous, parallel connections between Layer 2 Ethernet segments. Switched connections between Ethernet segments last only for the duration of the packet. New connections can be made between different segments for the next packet.
Cisco switches that support Layer 2 Ethernet ports solve congestion problems caused by high-bandwidth devices and by a large number of users by assigning each device (for example, a server) to its own 10-, 100-, or 1000-Mbps collision domain. Because each LAN port connects to a separate Ethernet collision domain, servers in a properly configured switched environment achieve full access to the bandwidth.
Because collisions cause significant congestion in Ethernet networks, an effective solution is full-duplex communication. Normally, Ethernet operates in half-duplex mode, which means that stations can either receive or transmit. In full-duplex mode, two stations can transmit and receive at the same time. When packets can flow in both directions simultaneously, the effective Ethernet bandwidth doubles.
Switching Frames Between Segments
Each Layer 2 Ethernet port can connect to a single workstation or server, or to a hub through which workstations or servers connect to the network.
On a typical Ethernet hub, all ports connect to a common backplane within the hub, and the bandwidth of the network is shared by all devices attached to the hub. If two stations establish a session that uses a significant level of bandwidth, the network performance of all other stations attached to the hub is degraded.
To reduce degradation, the switch considers each LAN port to be an individual segment. When stations connected to different LAN ports need to communicate, the switch forwards frames from one LAN port to the other at wire speed to ensure that each session receives full bandwidth.
To switch frames between LAN ports efficiently, the switch maintains an address table. When a frame enters the switch, it associates the MAC address of the sending network device with the LAN port on which it was received.
Building the MAC Address Table
The MAC address table is built by using the source MAC address of the frames received. When the switch receives a frame for a destination MAC address not listed in its address table, it floods the frame to all LAN ports of the same VLAN except the port that received the frame. When the destination station replies, the switch adds its relevant source MAC address and port ID to the address table. The switch then forwards subsequent frames to a single LAN port without flooding to all LAN ports.
In PFC3C and PFC3CXL mode, the MAC address table can store at 96,000 address entries (for other PFC3 modes, 64,000 address entries) without flooding any entries. The switch uses an aging mechanism, defined by a configurable aging timer, so if a MAC address remains inactive for a specified number of seconds, it is removed from the address table.
Synchronization and Sharing of the MAC Address Table
With distributed switching, each DFC-equipped switching module learns MAC addresses, maintains a MAC address table, and ages table entries. By enabling MAC address table synchronization over the Ethernet Out of Band Channel (EOBC), you can configure the switch to allow sharing and synchronization of the address tables among all DFCs and supervisor engines in the switch, eliminating the need for flooding by a DFC for an address that is active on another DFC. In VSS mode or when a WS-6708-10G switching module is present in the system, MAC synchronization is automatically enabled. Otherwise, MAC synchronization must be enabled manually by entering the mac-address-table synchronize command.
Notification of Address Table Changes
You can configure the switch to maintain a history of dynamic additions and removals of address table entries associated with a particular LAN port. The change history can be sent as an SNMP trap notification or it can be read manually from the SNMP MIB.
Understanding VLAN Trunks
These sections describe VLAN trunks in Cisco IOS Release 12.2SX:
Trunking Overview
Note For information about VLANs, see Chapter23, “Configuring VLANs”
A trunk is a point-to-point link between the switch and another networking device. Trunks carry the traffic of multiple VLANs over a single link and allow you to extend VLANs across an entire network.
Two trunking encapsulations are available on all Ethernet ports:
Note The following switching modules do not support ISL encapsulation:
• WS-X6502-10GE
• WS-X6548-GE-TX, WS-X6548V-GE-TX, WS-X6548-GE-45AF
• WS-X6148-GE-TX, WS-X6148V-GE-TX, WS-X6148-GE-45AF
You can configure a trunk on a single Ethernet port or on an EtherChannel. For more information about EtherChannel, see Chapter19, “Configuring EtherChannels”
Ethernet trunk ports support several trunking modes (see Table 17-2). You can specify whether the trunk uses ISL or 802.1Q encapsulation, and if the encapsulation type is autonegotiated.
Note You can configure LAN ports to negotiate the encapsulation type. You cannot configure WAN interfaces to negotiate the encapsulation type.
The Dynamic Trunking Protocol (DTP) manages trunk autonegotiation on LAN ports. DTP supports autonegotiation of both ISL and 802.1Q trunks.
To autonegotiate trunking, the LAN ports must be in the same VTP domain. Use the trunk or nonegotiate keywords to force LAN ports in different domains to trunk. For more information on VTP domains, see Chapter22, “Configuring VTP”
Encapsulation Types
Table 17-1 lists the Ethernet trunk encapsulation types.
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Specifies ISL encapsulation on the trunk link. Note Some modules do not support ISL encapsulation (see the “Trunking Overview” section). |
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Specifies that the LAN port negotiate with the neighboring LAN port to become an ISL (preferred) or 802.1Q trunk, depending on the configuration and capabilities of the neighboring LAN port. |
The trunking mode, the trunk encapsulation type, and the hardware capabilities of the two connected LAN ports determine whether a link becomes an ISL or 802.1Q trunk.
Layer 2 LAN Port Modes
Table 17-2 lists the Layer 2 LAN port modes and describes how they function on LAN ports.
Note DTP is a point-to-point protocol. However, some internetworking devices might forward DTP frames improperly. To avoid this problem, ensure that LAN ports connected to devices that do not support DTP are configured with the access keyword if you do not intend to trunk across those links. To enable trunking to a device that does not support DTP, use the nonegotiate keyword to cause the LAN port to become a trunk but not generate DTP frames.
Default Layer 2 LAN Interface Configuration
Table 17-3 shows the Layer 2 LAN port default configuration.
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VLANs 1 to 4094, except reserved VLANs (see Table 23-1) |
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Layer 2 LAN Interface Configuration Guidelines and Restrictions
When configuring Layer 2 LAN ports, follow these guidelines and restrictions:
– WS-X6548-GE-TX, WS-X6548V-GE-TX, WS-X6548-GE-45AF
– WS-X6148-GE-TX, WS-X6148V-GE-TX, WS-X6148-GE-45AF
- The following configuration guidelines and restrictions apply when using 802.1Q trunks and impose some limitations on the trunking strategy for a network. Note these restrictions when using 802.1Q trunks:
– When connecting Cisco switches through an 802.1q trunk, make sure the native VLAN for an 802.1Q trunk is the same on both ends of the trunk link. If the native VLAN on one end of the trunk is different from the native VLAN on the other end, spanning tree loops might result.
– Disabling spanning tree on the native VLAN of an 802.1Q trunk without disabling spanning tree on every VLAN in the network can cause spanning tree loops. We recommend that you leave spanning tree enabled on the native VLAN of an 802.1Q trunk. If this is not possible, disable spanning tree on every VLAN in the network. Make sure your network is free of physical loops before disabling spanning tree.
– When you connect two Cisco switches through 802.1Q trunks, the switches exchange spanning tree BPDUs on each VLAN allowed on the trunks. The BPDUs on the native VLAN of the trunk are sent untagged to the reserved IEEE 802.1d spanning tree multicast MAC address (01-80-C2-00-00-00). The BPDUs on all other VLANs on the trunk are sent tagged to the reserved Cisco Shared Spanning Tree (SSTP) multicast MAC address (01-00-0c-cc-cc-cd).
– Non-Cisco 802.1Q switches maintain only a single instance of spanning tree (the Mono Spanning Tree, or MST) that defines the spanning tree topology for all VLANs. When you connect a Cisco switch to a non-Cisco switch through an 802.1Q trunk, the MST of the non-Cisco switch and the native VLAN spanning tree of the Cisco switch combine to form a single spanning tree topology known as the Common Spanning Tree (CST).
– Because Cisco switches transmit BPDUs to the SSTP multicast MAC address on VLANs other than the native VLAN of the trunk, non-Cisco switches do not recognize these frames as BPDUs and flood them on all ports in the corresponding VLAN. Other Cisco switches connected to the non-Cisco 802.1q cloud receive these flooded BPDUs. This allows Cisco switches to maintain a per-VLAN spanning tree topology across a cloud of non-Cisco 802.1Q switches. The non-Cisco 802.1Q cloud separating the Cisco switches is treated as a single broadcast segment between all switches connected to the non-Cisco 802.1q cloud through 802.1q trunks.
– Make certain that the native VLAN is the same on all of the 802.1q trunks connecting the Cisco switches to the non-Cisco 802.1q cloud.
– If you are connecting multiple Cisco switches to a non-Cisco 802.1q cloud, all of the connections must be through 802.1q trunks. You cannot connect Cisco switches to a non-Cisco 802.1q cloud through ISL trunks or through access ports. Doing so causes the switch to place the ISL trunk port or access port into the spanning tree “port inconsistent” state and no traffic will pass through the port.
Configuring LAN Interfaces for Layer 2 Switching
These sections describe how to configure Layer 2 switching in Cisco IOS Release 12.2SX:
- Configuring a LAN Port for Layer 2 Switching
- Enabling Out-of-Band MAC Address Table Synchronization
- Configuring MAC Address Table Notification
- Configuring a Layer 2 Switching Port as a Trunk
- Configuring a LAN Interface as a Layer 2 Access Port
- Configuring an IEEE 802.1Q Custom EtherType Field Value
Note Use the default interface {ethernet | fastethernet | gigabitethernet | tengigabitethernet} slot/port command to revert an interface to its default configuration.
Configuring a LAN Port for Layer 2 Switching
To configure a LAN port for Layer 2 switching, perform this task:
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Router(config)# interface type 1 slot/port |
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(Optional) Shuts down the interface to prevent traffic flow until configuration is complete. |
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Configures the LAN port for Layer 2 switching. Note You must enter the switchport command once without any keywords to configure the LAN port as a Layer 2 port before you can enter additional switchport commands with keywords. |
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Activates the interface. (Required only if you shut down the interface.) |
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Router# show running-config interface [ type 1 slot/port ] |
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Router# show interfaces [ type 1 slot/port ] switchport |
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Router# show interfaces [ type 1 slot/port ] trunk |
1.type = fastethernet, gigabitethernet, or tengigabitethernet |
After you enter the switchport command, the default mode is switchport mode dynamic desirable. If the neighboring port supports trunking and is configured to allow trunking, the link becomes a Layer 2 trunk when you enter the switchport command. By default, LAN trunk ports negotiate encapsulation. If the neighboring port supports ISL and 802.1Q encapsulation and both ports are set to negotiate the encapsulation type, the trunk uses ISL encapsulation (10-Gigabit Ethernet ports do not support ISL encapsulation).
Note When using the switchport command, if a port configured for Layer 3 is now configured for Layer 2, the configuration for Layer 3 is retained in the memory but not in the running configuration and is applied to the port whenever the port switches back to Layer 3. Also, if a port configured for Layer 2 is now configured for Layer 3, the configuration for Layer 2 is retained in the memory but not in the running configuration and is applied to the port whenever the port switches back to Layer 2. To restore the default configuration of the port in the memory and in the running configuration, use the default interface command. To avoid potential issues while changing the role of a port using the switchport command, shut down the interface before applying the switchport command.
Enabling Out-of-Band MAC Address Table Synchronization
With Release 12.2(33)SXF and later releases, to enable the out-of-band MAC address table synchronization feature, perform this task:
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Router(config)# [ no ] mac-address-table synchronize [ activity-time seconds ] |
Enables out-of-band synchronization of MAC address tables among DFC-equipped switching modules. |
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When configuring out-of-band MAC address table synchronization, note the following information:
- By default, out-of-band MAC address table synchronization is disabled.
- Out-of-band MAC address table synchronization is enabled automatically if any of the following conditions are met:
– A WS-6708-10G switching module is installed in the switch.
– The switch is part of a virtual switch system (VSS) running Cisco IOS Release 12.2(33)SXI4 or a later release.
- The activity timer interval can be configured as 160, 320, and 640 seconds. The default is 160 seconds.
This example shows how to enable out-of-band MAC address table synchronization:
Configuring MAC Address Table Notification
Note ● Complete the steps in the “Configuring a LAN Port for Layer 2 Switching” section before performing the tasks in this section.
- To send SNMP trap notifications using this feature, you must also enable the global MAC trap flag, using the snmp-server enable mac-notification change command.
With Release 12.2(33)SXH and later releases, to configure the MAC address table notification feature, perform this task:
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Router(config)# mac-address-table notification change [ interval value ] [ history size ] |
Enables sending notification of dynamic changes to MAC address table. (Optional) Sets the minimum change-sending interval in seconds. (Optional) Sets the number of entries in the history buffer. Note The no form of the command reverts to the default without sending any change information. |
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Router(config)# interface type 2 slot/port |
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Router(config-if)# snmp trap mac-notification change [ added | removed ] |
For MAC addresses that are associated with this LAN port, enable SNMP trap notification when MAC addresses are added to or removed from the address table. (Optional) To notify only when a MAC address is added to the table, use the added option. To notify only when a MAC address is removed, use the removed option. |
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Displays whether this feature is enabled, the notification interval, and the history table maximum size. Displays history table contents. |
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Router# show mac-address-table notification [ type slot/port ] |
Displays the interface-specific flags for the specified interface. If slot and port are not specified, the flags for all interfaces will be displayed. |
2.type = fastethernet, gigabitethernet, or tengigabitethernet |
When configuring the notification parameters, note the following information:
- The interval value parameter can be configured from 0 seconds (immediate) to 2,147,483,647 seconds. The default is 1 second.
- The history size parameter can be configured from 0 entries to 500 entries. The default is 1 entry.
This example shows how to configure the SNMP notification of dynamic additions to the MAC address table of addresses on the Fast Ethernet ports 5/7 and 5/8. Notifications of changes will be sent no more frequently than 5 seconds, and up to 25 changes can be stored and sent in that interval:
Configuring a Layer 2 Switching Port as a Trunk
These sections describe configuring a Layer 2 switching port as a trunk:
- Configuring the Layer 2 Switching Port as an ISL or 802.1Q Trunk
- Configuring the Layer 2 Trunk to Use DTP
- Configuring the Layer 2 Trunk Not to Use DTP
- Configuring the Access VLAN
- Configuring the 802.1Q Native VLAN
- Configuring the List of VLANs Allowed on a Trunk
- Configuring the List of Prune-Eligible VLANs
- Completing Trunk Configuration
- Verifying Layer 2 Trunk Configuration
- Configuration and Verification Examples
Configuring the Layer 2 Switching Port as an ISL or 802.1Q Trunk
Note ● Complete the steps in the “Configuring a LAN Port for Layer 2 Switching” section before performing the tasks in this section.
- When you enter the switchport command with no other keywords (Step 3 in the previous section), the default mode is switchport mode dynamic desirable and switchport trunk encapsulation negotiate.
To configure the Layer 2 switching port as an ISL or 802.1Q trunk, perform this task:
When configuring the Layer 2 switching port as an ISL or 802.1Q trunk, note the following information:
- The switchport mode trunk command (see the “Configuring the Layer 2 Trunk Not to Use DTP” section) is not compatible with the switchport trunk encapsulation negotiate command.
- To support the switchport mode trunk command, you must configure the encapsulation as either ISL or 802.1Q.
- The following switching modules do not support ISL encapsulation:
– WS-X6548-GE-TX, WS-X6548V-GE-TX, WS-X6548-GE-45AF
– WS-X6148-GE-TX, WS-X6148V-GE-TX, WS-X6148-GE-45AF
Note Complete the steps in the “Completing Trunk Configuration” section after performing the tasks in this section.
Configuring the Layer 2 Trunk to Use DTP
Note Complete the steps in the “Configuring a LAN Port for Layer 2 Switching” section before performing the tasks in this section.
To configure the Layer 2 trunk to use DTP, perform this task:
When configuring the Layer 2 trunk to use DTP, note the following information:
- Required only if the interface is a Layer 2 access port or to specify the trunking mode.
- See Table 17-2 for information about trunking modes.
Note Complete the steps in the “Completing Trunk Configuration” section after performing the tasks in this section.
Configuring the Layer 2 Trunk Not to Use DTP
Note Complete the steps in the “Configuring a LAN Port for Layer 2 Switching” section before performing the tasks in this section.
To configure the Layer 2 trunk not to use DTP, perform this task:
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When configuring the Layer 2 trunk not to use DTP, note the following information:
- Before entering the switchport mode trunk command, you must configure the encapsulation (see the “Configuring the Layer 2 Switching Port as an ISL or 802.1Q Trunk” section).
- To support the switchport nonegotiate command, you must enter the switchport mode trunk command.
- Enter the switchport mode dynamic trunk command. See Table 17-2 for information about trunking modes.
- Before entering the switchport nonegotiate command, you must configure the encapsulation (see the “Configuring the Layer 2 Switching Port as an ISL or 802.1Q Trunk” section) and configure the port to trunk unconditionally with the switchport mode trunk command (see the “Configuring the Layer 2 Trunk to Use DTP” section).
Note Complete the steps in the “Completing Trunk Configuration” section after performing the tasks in this section.
Configuring the Access VLAN
Note Complete the steps in the “Configuring a LAN Port for Layer 2 Switching” section before performing the tasks in this section.
To configure the access VLAN, perform this task:
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(Optional) Configures the access VLAN, which is used if the interface stops trunking. The vlan_ID value can be 1 through 4094, except reserved VLANs (see Table 23-1).
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Note Complete the steps in the “Completing Trunk Configuration” section after performing the tasks in this section.
Configuring the 802.1Q Native VLAN
Note Complete the steps in the “Configuring a LAN Port for Layer 2 Switching” section before performing the tasks in this section.
To configure the 802.1Q native VLAN, perform this task:
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(Optional) Configures the 802.1Q native VLAN. Note If VLAN locking is enabled, enter the VLAN name instead of the VLAN number. For more information, see the “VLAN Locking” section. |
When configuring the native VLAN, note the following information:
- The vlan_ID value can be 1 through 4094, except reserved VLANs (see Table 23-1).
- The access VLAN is not automatically used as the native VLAN.
Note Complete the steps in the “Completing Trunk Configuration” section after performing the tasks in this section.
Configuring the List of VLANs Allowed on a Trunk
Note Complete the steps in the “Configuring a LAN Port for Layer 2 Switching” section before performing the tasks in this section.
To configure the list of VLANs allowed on a trunk, perform this task:
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Router(config-if)# switchport trunk allowed vlan { add | except | none | remove } vlan [, vlan [, vlan [,...]] |
(Optional) Configures the list of VLANs allowed on the trunk.
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When configuring the list of VLANs allowed on a trunk, note the following information:
- The vlan parameter is either a single VLAN number from 1 through 4094, or a range of VLANs described by two VLAN numbers, the lesser one first, separated by a dash. Do not enter any spaces between comma-separated vlan parameters or in dash-specified ranges.
- If VLAN locking is enabled, enter VLAN names instead of VLAN numbers. When entering a range of VLAN names, you must leave spaces between the VLAN names and the dash.
- All VLANs are allowed by default.
- You can remove VLAN 1. If you remove VLAN 1 from a trunk, the trunk interface continues to send and receive management traffic, for example, Cisco Discovery Protocol (CDP), VLAN Trunking Protocol (VTP), Port Aggregation Protocol (PAgP), and DTP in VLAN 1.
Note Complete the steps in the “Completing Trunk Configuration” section after performing the tasks in this section.
Configuring the List of Prune-Eligible VLANs
Note Complete the steps in the “Configuring a LAN Port for Layer 2 Switching” section before performing the tasks in this section.
To configure the list of prune-eligible VLANs on the Layer 2 trunk, perform this task:
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Router(config-if)# switchport trunk pruning vlan { none |{{ add | except | remove } vlan [, vlan [, vlan [,...]]}} |
(Optional) Configures the list of prune-eligible VLANs on the trunk (see the “Understanding VTP Pruning” section). Note The no form of the command reverts to the default value (all VLANs prune-eligible). |
When configuring the list of prune-eligible VLANs on a trunk, note the following information:
- The vlan parameter is either a single VLAN number from 1 through 4094, except reserved VLANs (see Table 23-1), or a range of VLANs described by two VLAN numbers, the lesser one first, separated by a dash. Do not enter any spaces between comma-separated vlan parameters or in dash-specified ranges.
- The default list of VLANs allowed to be pruned contains all VLANs.
- Network devices in VTP transparent mode do not send VTP Join messages. On trunk connections to network devices in VTP transparent mode, configure the VLANs used by the transparent-mode network devices or that need to be carried across the transparent-mode network devices as pruning ineligible.
Note Complete the steps in the “Completing Trunk Configuration” section after performing the tasks in this section.
Completing Trunk Configuration
To complete Layer 2 trunk configuration, perform this task:
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Activates the interface. (Required only if you shut down the interface.) |
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Verifying Layer 2 Trunk Configuration
To verify Layer 2 trunk configuration, perform this task:
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Router# show running-config interface type3 slot/port |
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3.type = fastethernet, gigabitethernet, or tengigabitethernet |
Configuration and Verification Examples
This example shows how to configure the Fast Ethernet port 5/8 as an 802.1Q trunk. This example assumes that the neighbor port is configured to support 802.1Q trunking:
This example shows how to verify the configuration:
Configuring a LAN Interface as a Layer 2 Access Port
To configure a LAN port as a Layer 2 access port, perform this task:
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Router(config)# interface type 4 slot/port |
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(Optional) Shuts down the interface to prevent traffic flow until configuration is complete. |
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Configures the LAN port for Layer 2 switching. Note You must enter the switchport command once without any keywords to configure the LAN port as a Layer 2 port before you can enter additional switchport commands with keywords. |
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Places the LAN port in a VLAN. The vlan_ID value can be 1 through 4094, except reserved VLANs (see Table 23-1). Note If VLAN locking is enabled, enter the VLAN name instead of the VLAN number. For more information, see the “VLAN Locking” section. |
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Activates the interface. (Required only if you shut down the interface.) |
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Router# show running-config interface [ type 1 slot/port ] |
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Router# show interfaces [ type 1 slot/port ] switchport |
4.type = fastethernet, gigabitethernet, or tengigabitethernet |
This example shows how to configure the Fast Ethernet port 5/6 as an access port in VLAN 200:
This example shows how to verify the configuration:
Configuring an IEEE 802.1Q Custom EtherType Field Value
You can configure a custom EtherType field value on a port to support network devices that do not use the standard 0x8100 EtherType field value on 802.1Q-tagged or 802.1p-tagged frames.
To configure a custom value for the EtherType field, perform this task:
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When configuring a custom EtherType field value, note the following information:
- To use a custom EtherType field value, all network devices in the traffic path across the network must support the custom EtherType field value.
- You can configure a custom EtherType field value on trunk ports, access ports, and tunnel ports.
- You can configure a custom EtherType field value on the member ports of an EtherChannel.
- You cannot configure a custom EtherType field value on a port-channel interface.
- Each port supports only one EtherType field value. A port that is configured with a custom EtherType field value does not recognize frames that have any other EtherType field value as tagged frames. For example, a trunk port that is configured with a custom EtherType field value does not recognize the standard 0x8100 EtherType field value on 802.1Q-tagged frames and cannot put the frames into the VLAN to which they belong.
- See the Release Notes for Cisco IOS Release 12.2SX for a list of the modules that support custom IEEE 802.1Q EtherType field values.
This example shows how to configure the EtherType field value to 0x1234: