Switch CLI, STP, Link Aggregation & Stacking

🧭 Cisco IOS CLI Mode Hierarchy (Live State Tracker)

Notice how the command prompt changes as you move deeper into configuration modes.

Current: User EXEC (Switch>)

1. User EXEC Switch>

Limited view-only mode. Cannot view full config or change settings.

Next: Type enable

2. Privileged EXEC Switch#

Run all show diagnostics (`show interfaces`, `show mac address-table`, `show spanning-tree`).

Next: configure terminal

3. Global Config Switch(config)#

Modify switch-wide settings (hostname, STP priority, VLANs).

Next: interface fa0/1

4. Interface Config Switch(config-if)#

Enable/disable a specific port (shutdown / no shutdown) or bundle LACP.

Back: exit or end

🔌 Interactive Switch Faceplate & Port States (`show interfaces`)

Click any port to inspect its Layer 1 (Physical Status) vs. Layer 2 (Line Protocol) state, or toggle physical cables.

CISCO CATALYST 2960-24TT Hostname: Switch

up/up (Forwarding) STP Blocked Admin Down (`shutdown`) down/down (No Cable)

Understanding `show interfaces` Port Status Codes Layer 1 / Layer 2

FastEthernet0/1 is up, line protocol is up (connected)

Cable is plugged in (Layer 1 UP) and keepalives/frames are flowing normally (Layer 2 UP).

up/up

FastEthernet0/4 is down, line protocol is down (notconnect)

Port is enabled in config, but no cable is attached or connected PC is powered off.

down/down

FastEthernet0/3 is administratively down, line protocol is down (disabled)

An administrator disabled the port using shutdown. Fix with no shutdown.

admin down

Cisco IOS Console — Switch0 (TTY0)

Quick Insert:

Cisco IOS Software, C2960 Software (C2960-LANBASEK9-M), Version 15.0(2)SE4

Type ? or help for available commands in your current mode.

Tip: Complete the 7 Guided Lab Missions in the right panel!

🌲 Spanning Tree Protocol (STP — IEEE 802.1D / Rapid PVST+)

Redundant switch links prevent single points of failure, but create fatal Layer 2 Broadcast Storms without STP.

Click any switch priority button below to change the Root Bridge Election (Lowest Bridge ID wins!). Root Bridge: SW1 (Priority 4096)

SW1 Bridge Priority

MAC: 000A.1111.1111

SW2 Bridge Priority

MAC: 000B.2222.2222

SW3 Bridge Priority

MAC: 000C.3333.3333

👑 Root Bridge & Root Port (RP)

The switch with the lowest Bridge ID (Priority + MAC) becomes the Root Bridge. Every non-root switch selects ONE Root Port (RP) with the lowest cost path back to the Root Bridge.

🟢 Designated Port (DP)

Every network segment has one Designated Port (DP) that forwards traffic toward the Root. All ports on the Root Bridge are always Designated Ports (`FWD`).

🟠 Blocked / Alternate Port (BLK)

Ports that are neither RP nor DP are placed in Blocking (`BLK`) state. They drop data frames to prevent loops, but listen for BPDUs to take over immediately if a link fails!

🔗 Link Aggregation (EtherChannel / IEEE 802.3ad LACP)

See why adding a second physical cable between two switches doesn't increase bandwidth unless you configure Link Aggregation!

Current Mode: NO Link Aggregation (2 Separate Physical Links) Effective Bandwidth: 1 Gbps (1 Link Blocked by STP!)

Why Link Aggregation (EtherChannel) Matters

Combines Bandwidth: Bundles up to 8 physical ports into a single logical link (`Port-channel1` or `Po1`).
STP Friendly: Spanning Tree treats the entire bundle as one single logical interface, so it doesn't block redundant cables!
Load Balancing & Redundancy: Traffic is load-balanced across active links; if one cable fails, traffic continues uninterrupted in milliseconds.

Cisco IOS Configuration & Protocol Modes

Switch(config)# interface range gi0/1 - 2
Switch(config-if-range)# channel-group 1 mode active
Switch(config-if-range)# end
Switch# show etherchannel summary

LACP (IEEE 802.3ad Standard): uses active / passive. PAgP (Cisco Proprietary): uses desirable / auto.

📚 Switch Stacking (Cisco StackWise Backplane)

How connecting physical switches into a Stack differs from merely chaining standalone switches with uplink cables.

3-Switch Stack (1 Single Logical Switch & 1 IP Address) Full Ring: 32 Gbps

Switch 1 *Active / Stack Master

Ports: Gi1/0/1 through Gi1/0/24 | Priority: 15

Rear Stack Port A ⇅

Rear Stack Port B ⇅

Switch 2 Standby Master

Ports: Gi2/0/1 through Gi2/0/24 | Priority: 10

Rear Stack Port A ⇅

Rear Stack Port B ⇅

Switch 3 Member

Ports: Gi3/0/1 through Gi3/0/24 | Priority: 1

Rear Stack Port A ⇅

Rear Stack Port B ⇅

Understanding Stacked Port Naming: Gi 2 / 0 / 15

2

Stack Member #

0

Module / Slot #

15

Port Number

Switch Stacking vs. Standalone Uplinked Switches

Feature	Standalone	Stacked
Management CLI	Separate IP per switch	1 Single CLI & IP
Interconnect	Front Ethernet ports	Rear StackWise Ring
Port Numbering	Gi0/1 on each	Gi1/0/1, Gi2/0/1...
Cross-Switch LACP	Not possible	Supported!

Switch# show switch

Switch/Stack Mac Address : 0024.97b1.4200
                                           H/W   Current
Switch#  Role   Mac Address     Priority Version  State 
----------------------------------------------------------
*1       Master 0024.97b1.4200     15     0       Ready               
 2       Member 0024.97b1.4280     10     0       Ready               
 3       Member 0024.97b1.4300     1      0       Ready

Layer 2 Switching Mastery Lab

🧭 Cisco IOS CLI Mode Hierarchy (Live State Tracker)

🔌 Interactive Switch Faceplate & Port States (`show interfaces`)

🌲 Spanning Tree Protocol (STP — IEEE 802.1D / Rapid PVST+)

🔗 Link Aggregation (EtherChannel / IEEE 802.3ad LACP)

📚 Switch Stacking (Cisco StackWise Backplane)

📝 Chapter Concept Review Quiz

🎓 Student Lab Verification & Completion Report