CCNA 200-301 v1.1 reference — Network Access

Trunks and 802.1Q

802.1Q tagging, native VLAN behavior, allowed VLAN lists, and how to configure and verify trunk links between switches.

Objective 2.2v1.1 exam target

A trunk carries multiple VLANs over one link. 802.1Q inserts a 4-byte tag between source MAC and EtherType containing the VLAN ID (12 bits → 1–4094). The receiving switch reads the tag and forwards the frame into that VLAN — the tag never reaches the host.

The native VLAN is the one VLAN whose frames travel the trunk untagged. Both ends must agree: a native VLAN mismatch leaks traffic between the two different VLANs and generates mismatch warnings. Default native VLAN is 1 — changing it is common hardening.

802.1Q tag anatomy

Field	Size	Contents
TPID	16 bits	0x8100 — marks the frame as tagged
PRI (PCP)	3 bits	802.1p priority for QoS
DEI/CFI	1 bit	Drop eligible indicator
VID	12 bits	VLAN ID 0–4095

Configure and verify a trunk

Trunk two switches carrying VLANs 10, 20, 30 — Privileged EXEC → Interface configuration

Cisco IOS / IOS XE

configure terminal
interface gigabitethernet1/0/24
 switchport trunk encapsulation dot1q
 switchport mode trunk
 switchport trunk native vlan 99
 switchport trunk allowed vlan 10,20,30,99
 end

Verify

show interfaces trunk
show interfaces gi1/0/24 switchport

Port listed with mode trunk and encapsulation 802.1q.
Native VLAN matches on both ends; allowed-and-active list shows 10,20,30,99.

switchport trunk encapsulation dot1q is required only on models that still support ISL.
VLANs must exist and be active to appear in the 'spanning-tree forwarding' state.

Changes device configuration.

$ show interfaces trunk (interpreted)

Port Mode Encapsulation Status Native vlanMode and native VLAN at a glance.

Gi1/0/24 on 802.1q trunking 99Confirm native VLAN matches the far end.

Port Vlans allowed on trunkAdministrative allowed list.

Gi1/0/24 10,20,30,99What you permitted.

Port Vlans allowed and active in management domainAllowed AND existing/active VLANs.

Gi1/0/24 10,20,30,99A VLAN missing here exists nowhere in the path.

On this page

A trunk carries multiple VLANs over one …
The native VLAN is the one VLAN whose fr…
802.1Q tag anatomy
Configure and verify a trunk
show interfaces trunk (interpreted)

Handbook sections

Related resources

Practise this topic Source topic 17: VLANs (Part 2 - Trunks & ROAS)Practise topic 17 deck Source topic 19: DTP & VTP Practise topic 19 deck

Sources

Cisco CCNA 200-301 v1.1 Exam Topics (official PDF) — reviewed 2026-11-02
IEEE 802.1 Working Group — reviewed 2026-11-02
Cisco — LAN Switching Command Reference — reviewed 2026-11-02

Targets CCNA 200-301 v1.1 objectives. Supplemental blocks are labeled beyond exam scope.