Spanning Tree Protocol

BPDU Filtering

Disables BPDUs on a port(Dangerous)

Requires PortFast

Loss of BPDUs

Loop Guard

Simply detects loss of BPDUs

W/O Loop Guard: Port Starts Forwarding

With Loop Guard: Port Becomes Loop-inconsistent

Doesn't actually detect unidirecitonal links

UDLD

Unidirecitonal Link Detection

Works by sending keepalives

Portfast

UplinkFast

BackboneFast

802.1D Traditional STP

Port Roles

Root Port

Designated Port

Blocking Port

Port States

Disabled

Blocking

Listening

Learning

Forwarding

Timers

Hello Time (2 Seconds)

Forward Delay(15 Seconds)

MaxAge (20 Seconds)

CST

Common Spanning Tree

1 instace of STP

Over the Native VLAN

dot1Q based

PVST

Per-VLAN Spanning Tree

1 instance of STP per VLAN

ISL Based

PVST+

Per-VLAN Spanning Tree Plus

Interoperability betwen CST/PVST

Operates over both dot1Q and ISL

802.1w RSTP

Port Roles

Root Port

Designated Port

Alternate Port

Backup Port

Port States

Discarding

Learning

Forwarding

Differences

BPDUs sent from all switches

Port Types

Edge port

Host Port

No longer edge if BPDU received

Root port

point-to-point port

Designated Port

If on a shared media(half duplex)

Must go through traditional 802.1D convergence

Because multiple switches might be involved.

RPVST+

Rapid Per-VLAN Spanning Tree

MST

Multiple Spanning Tree

IST

Internal Spanning Tree