VLAN & Trunk Cheat Sheet

The Layer-2 commands I keep reaching for, with the IOS and Junos spelling next to each other. Where a line is marked (IOS) or (Junos) only, the other platform has no direct equivalent.

VLANs

Task	Cisco IOS	Junos
Create a VLAN	`vlan 20` / `name Servers`	`set vlans servers vlan-id 20`
List VLANs	`show vlan brief`	`show vlans`
VLAN membership of a port	`show interfaces status`	`show ethernet-switching interfaces`

Access ports

! IOS
interface Gi1/0/5
 description Printer
 switchport mode access
 switchport access vlan 20
 spanning-tree portfast

# Junos
set interfaces ge-0/0/5 description Printer
set interfaces ge-0/0/5 unit 0 family ethernet-switching interface-mode access
set interfaces ge-0/0/5 unit 0 family ethernet-switching vlan members servers
set protocols rstp interface ge-0/0/5 edge

Trunk ports

! IOS
interface Gi1/0/48
 description Uplink to core
 switchport trunk encapsulation dot1q   ! older platforms only
 switchport mode trunk
 switchport trunk allowed vlan 10,20,30
 switchport trunk native vlan 999       ! unused VLAN as native
 switchport nonegotiate                 ! no DTP

# Junos
set interfaces ge-0/0/47 description "Uplink to core"
set interfaces ge-0/0/47 unit 0 family ethernet-switching interface-mode trunk
set interfaces ge-0/0/47 unit 0 family ethernet-switching vlan members [ users servers voice ]
set interfaces ge-0/0/47 native-vlan-id 999

Tip

Prune trunks to the VLANs that actually need to cross them, and never leave VLAN 1 as the native VLAN on a trunk that leaves the rack.

Spanning tree

Task	Cisco IOS	Junos
Mode	`spanning-tree mode rapid-pvst`	`set protocols rstp` (default on EX)
Root bridge	`spanning-tree vlan 1-4094 priority 4096`	`set protocols rstp bridge-priority 4k`
Edge port	`spanning-tree portfast`	`set protocols rstp interface ge-0/0/5 edge`
Protect edge ports	`spanning-tree bpduguard enable`	`set protocols rstp bpdu-block-on-edge`
Status	`show spanning-tree` / `show spanning-tree root`	`show spanning-tree bridge` / `show spanning-tree interface`

Port channels

! IOS - LACP
interface range Gi1/0/1-2
 channel-group 1 mode active
interface Port-channel1
 switchport mode trunk

# Junos - LACP
set chassis aggregated-devices ethernet device-count 2
set interfaces ge-0/0/0 ether-options 802.3ad ae0
set interfaces ge-0/0/1 ether-options 802.3ad ae0
set interfaces ae0 aggregated-ether-options lacp active
set interfaces ae0 unit 0 family ethernet-switching interface-mode trunk

Troubleshooting

What	Cisco IOS	Junos
MAC table	`show mac address-table`	`show ethernet-switching table`
Where is a MAC?	`show mac address-table address aaaa.bbbb.cccc`	`show ethernet-switching table \| match aa:bb:cc`
Neighbours	`show cdp neighbors` / `show lldp neighbors`	`show lldp neighbors`
Errors on a port	`show interfaces Gi1/0/5 \| include error`	`show interfaces ge-0/0/5 extensive \| match error`
Trunk check	`show interfaces trunk`	`show ethernet-switching interfaces ge-0/0/47`

Last updated on October 17, 2026