Lab Simulation 67 Please use the "Tasks" and "Topology" tabs to complete this lablet. Topology Tasks Task 1 Configure 802.1q trunks between Sw1 and Sw2 on ports E0/0 and E0/1. - Add VLAN 99 as the nat

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Explanation

Lab Simulation 67: 802.1Q Trunks + LACP Port Channel

Overall Goal

This lab achieves two things in sequence:

1. Trunk links - Make E0/0 and E0/1 carry tagged traffic for VLANs 99 and 110, with VLAN 99 untagged (native).
2. Link Aggregation - Bundle those two physical links into a single logical channel (Port-channel 20) using LACP, then re-apply trunk config to the logical interface.

The order matters: configure trunks first on physical interfaces, then bundle them into the Port Channel, then re-apply trunk config to the Port Channel interface itself.

Step-by-Step Breakdown

Task 1: Configure 802.1Q Trunks

Step 1: configure terminal Enters global configuration mode. Required before any interface or feature configuration.

Step 2: interface range Ethernet0/0 - 1 Selects both interfaces simultaneously. This ensures identical configuration on both links - a mismatch between E0/0 and E0/1 would cause inconsistencies when they're later bundled.

Skip it? Configuring each interface separately risks typos causing asymmetric configs, which will prevent Port Channel formation.

Step 3: switchport trunk encapsulation dot1q Specifies 802.1Q as the VLAN tagging protocol (as opposed to ISL, Cisco's legacy proprietary alternative).

Skip it? On older IOS/IOSv platforms, the port defaults to "negotiate" encapsulation. If ISL is negotiated instead, the trunk won't work with modern equipment. This step is mandatory before setting trunk mode on those platforms.

Step 4: switchport mode trunk Forces the port into permanent trunking mode - it won't wait for DTP negotiation.

Skip it? The port stays in access mode (or dynamic mode), and VLAN tagging won't occur. No inter-switch VLAN traffic will pass.

Step 5: switchport trunk native vlan 99 Designates VLAN 99 as the native VLAN - frames on VLAN 99 cross the trunk untagged. The native VLAN must match on both ends of a trunk link.

Skip it? Both switches default to native VLAN 1. The lab explicitly requires VLAN 99. A native VLAN mismatch generates CDP/STP warnings and can cause traffic to land in the wrong VLAN - a security risk.

Step 6: switchport trunk allowed vlan 99,110 Restricts the trunk to carry only VLANs 99 and 110. By default, all VLANs (1-4094) are allowed.

Skip it? All VLANs traverse the trunk, violating the lab requirement and introducing unnecessary broadcast traffic and potential security exposure.

Step 7: exit Returns to global config mode, ending interface-range configuration.

Task 2: Configure LACP Port Channel

Step 8: configure terminal Re-enters global config mode (you exited in step 7). Technically redundant if you never left, but shown explicitly for clarity.

Step 9: interface range Ethernet0/0 - 1 Re-selects both physical interfaces to add them to the channel group.

Step 10: channel-group 20 mode active This is the core LACP command. It does two things:

• Assigns E0/0 and E0/1 to Port-channel 20
• Sets LACP mode to active - the switch actively sends LACP PDUs to initiate negotiation

LACP modes:

"Both links must negotiate" - this means both Sw1 and Sw2 must use active mode. Active-passive also works, but active-active guarantees negotiation happens regardless of which side initiates. mode on would be wrong here since it bypasses LACP entirely.

Skip it? The physical links remain independent. No Port-channel interface is created, and the bandwidth-aggregation and redundancy benefits are lost.

Step 11: exit Leaves the physical interface range.

Step 12: interface Port-channel 20 Enters the logical Port-channel interface. This is the interface the switch actually uses for traffic forwarding once the bundle is formed.

Steps 13-16: Re-apply trunk configuration to Port-channel 20

switchport trunk encapsulation dot1q
switchport mode trunk
switchport trunk native vlan 99
switchport trunk allowed vlan 99,110

This is the most commonly misunderstood part. When physical interfaces are bundled:

• The Port-channel interface becomes the operational interface
• Physical member configs may be overridden by the Port-channel config
• Applying trunk config here ensures it survives and is authoritative

Skip it? The Port-channel interface may default to access mode or allow all VLANs, causing VLAN filtering to silently stop working even though the physical ports looked correct.

Step 17: exit / Step 18: end Returns to privileged EXEC mode. end is a shortcut from any depth of config mode.

Step 19: copy running-config startup-config Saves configuration to NVRAM so it persists across reloads.

Skip it? A reload loses all changes. In a real environment this would be catastrophic. In the exam lab, the grader may check saved config.

What Goes Wrong Out of Order

Memory Tip

Think of it as "Dress the ports, then marry them, then dress the couple":

1. Dress the ports (Steps 3-6): Give E0/0 and E0/1 their trunk clothes (dot1q, native VLAN, allowed VLANs)
2. Marry them (Step 10): channel-group 20 mode active - they become one logical entity
3. Dress the couple (Steps 13-16): The Port-channel interface is who the network talks to now - it needs the same trunk clothes

A second mnemonic for LACP modes: "Active asks, Passive accepts, On ignores" - the lab wants both sides to ask, so both use active.

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