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200-301 · Question #1528

Lab Simulation 26 Guidelines This is a lab item in which tasks will be performed on virtual devices. - Refer to the Tasks tab to view the tasks for this lab item. - Refer to the Topology lab to access

Lab Simulation 26 - 802.1Q Trunking + LACP EtherChannel --- Overall Goal You're building a redundant, multi-VLAN trunk between SW-1 and SW-2 using: 802.1Q trunking to carry multiple VLANs over a single link while restricting which VLANs are allowed LACP EtherChannel (IEEE 802.3ad

Submitted by chiamaka_o· Mar 5, 2026Network Access

Question

Lab Simulation 26 Guidelines This is a lab item in which tasks will be performed on virtual devices. - Refer to the Tasks tab to view the tasks for this lab item. - Refer to the Topology lab to access the device console(s) and perform the tasks. - Console access is available for all required devices by clicking the device icon or using the tab(s) above the console window. - All necessary preconfigurations have been applied. - Do not change the enable password or hostname for any device. - Save your configurations to NVRAM before moving to the next item. - Click Next at the bottom of the screen to submit this lab and move to the next question. - When Next is clicked, the lab closes and cannot be reopened. Topology Tasks SW-3 and SW-4 are preconfigured with all necessary commands. All physical cabling is in place and verified. All connectivity must be operational. 1. Configure both SW-1 and SW-2 switch ports e0/0 and e0/1 for 802.1q trunking with only VLANS 1, 12, and 22 permitted. 2. Configure SW-1 port e0/2 for 802.1q trunking and include only VLANS 12 and 22. 3. Configure both SW-1 and SW-2 switch ports e0/0 and e0/1 for link aggregation using the industry standard protocol. All ports must be configured so that they immediately negotiate the link. Answer: Step 1: SW-1: interface e0/0 switchport mode trunk switchport trunk encapsulation dot1q switchport trunk allowed vlan 1,12,22 interface e0/1 switchport mode trunk switchport trunk encapsulation dot1q switchport trunk allowed vlan 1,12,22 SW-2: interface e0/0 switchport mode trunk switchport trunk encapsulation dot1q switchport trunk allowed vlan 1,12,22 interface e0/1 switchport mode trunk switchport trunk encapsulation dot1q switchport trunk allowed vlan 1,12,22 Step 2: SW-1: interface e0/2 switchport mode trunk switchport trunk encapsulation dot1q switchport trunk allowed vlan 12,22 Step 3: SW-1: interface range e0/0 - e0/1 channel-group 1 mode active SW-2: interface range e0/0 - e0/1 channel-group 1 mode active

Exhibits

Explanation

Lab Simulation 26 - 802.1Q Trunking + LACP EtherChannel

Overall Goal

You're building a redundant, multi-VLAN trunk between SW-1 and SW-2 using:

802.1Q trunking to carry multiple VLANs over a single link while restricting which VLANs are allowed
LACP EtherChannel (IEEE 802.3ad) to bundle two physical links into one logical high-bandwidth, fault-tolerant channel

The topology likely has SW-1 and SW-2 interconnected via e0/0 and e0/1, with SW-1's e0/2 connecting to another device (SW-3 or SW-4) that only needs VLANs 12 and 22.

Task 1 - Trunk Ports on SW-1 and SW-2 (e0/0, e0/1)

Steps 1-16

`interface e0/0` / `interface e0/1`

Enters interface config mode for the target port. All subsequent commands apply only to this interface.

`switchport trunk encapsulation dot1q`

Specifies 802.1Q as the trunking encapsulation method. On older Cisco IOS, switches may default to ISL (Cisco proprietary). This command is required before you can set the mode to trunk. If skipped, the switchport mode trunk command may fail or the switch will negotiate ISL, which is incompatible with non-Cisco equipment and violates the lab requirement.

`switchport mode trunk`

Hardcodes the port as a trunk - it stops sending DTP (Dynamic Trunking Protocol) negotiation and permanently operates as a trunk. If skipped, the port stays in access mode and carries only one VLAN, breaking multi-VLAN communication entirely.

`switchport trunk allowed vlan 1,12,22`

Restricts which VLANs are permitted to traverse this trunk. By default, a trunk allows all VLANs. Pruning to only 1, 12, and 22 improves security (limits broadcast domains) and reduces unnecessary traffic. If skipped, all VLANs flood through, which may expose traffic to unintended segments and fails the lab requirement.

Order matters: encapsulation must come before mode trunk on platforms that support both ISL and 802.1Q. Setting mode first on some IOS versions will throw an error.

Task 2 - SW-1 e0/2 Trunk (VLANs 12 and 22 only)

Steps 17-20

Same trunk configuration, but VLAN 1 is excluded. This is intentional - VLAN 1 is the default/native VLAN and often carries management traffic. The downstream device (SW-3 or SW-4) only participates in VLANs 12 and 22, so VLAN 1 is withheld for security/design reasons.

If VLAN 1 were included here, management traffic or unwanted broadcasts could leak to devices that shouldn't see them.

Task 3 - LACP EtherChannel (e0/0 + e0/1)

Steps 21-24

`interface range e0/0 - e0/1`

Applies the next command to both interfaces simultaneously - a shorthand that avoids repeating commands.

`channel-group 1 mode active`

This is the critical step. Breaking it down:

Component	Meaning
`channel-group 1`	Assigns the port to EtherChannel bundle #1
`mode active`	Uses LACP (IEEE 802.3ad - the "industry standard protocol") and actively initiates negotiation

Why active specifically? The question states ports must "immediately negotiate the link." LACP has two modes:

active - sends LACP PDUs immediately, initiates negotiation
passive - waits for the other side to initiate

If both sides were set to passive, neither would send LACP PDUs and the channel would never form. Setting both to active ensures immediate, automatic negotiation.

Using mode on would also bundle the ports, but that's a static/manual EtherChannel with no negotiation protocol - it's not LACP and doesn't meet the "industry standard protocol" requirement. Cisco's proprietary protocol is PAgP; LACP/802.3ad is the industry standard.

If EtherChannel were configured before trunking, the logical port-channel interface inherits settings from members, but mismatched configurations (e.g., one port trunk, one access) will cause the channel to fail or flap. Always configure trunking first, then aggregate.

What Would Break If Steps Were Out of Order or Skipped

Skipped Step	Consequence
`encapsulation dot1q`	`mode trunk` may fail; ISL negotiated instead
`mode trunk`	Port stays in access mode, only carries native VLAN
`allowed vlan`	All VLANs traverse the trunk (security/policy violation)
`channel-group mode active`	e0/0 and e0/1 remain separate physical links; no redundancy or aggregation
Using `passive` on both sides	LACP never negotiates; channel never forms

Memory Tips

Trunk order: "Encap before Mode, Mode before VLAN" - think E -> M -> V
LACP vs PAgP: "LACP = Law (industry standard/IEEE)"; PAgP = Proprietary (Cisco)
active/active: At least one side must be active. If unsure, make both active - it always works.
allowed vlan: Think of it as a whitelist - default is "all allowed," you're narrowing it down intentionally.

Topics

#VLAN Trunking#EtherChannel#LACP#Switchport Configuration

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