Spanning Tree Protocol Flashcards
Loop protection
- Connect two switches to each other
- They’ll send traffic back and forth forever
- There’s no “counting” mechanism at the MAC layer
- This is an easy way to bring down a network
- And somewhat difficult to troubleshoot
- Relatively easy to resolve
• IEEE standard 802.1D to prevent loops in bridged
(switched) networks (1990)
Switch operation
• Forwarding decisions made by MAC address
• Keeps a big table of MAC address that have been
seen
• All forwarding decisions are filtered through this list
• If the destination MAC is unknown, the frame is
flooded
• Sent to every switch port in the local subnet/VLAN
• Hopefully the destination station will respond
- Flooding is hopefully a temporary process
- Directed traffic resumes when the MAC is seen
STP port states
• Blocking - Not forwarding to prevent a loop
• Listening - Not forwarding and cleaning the MAC
table
• Learning - Not forwarding and adding to the MAC
table
• Forwarding - Data passes through and is fully
operational
• Disabled - Administrator has turned off the port
RSTP (802.1w)
- Rapid Spanning Tree Protocol (802.1w)
- A much-needed updated of STP
- This is the latest standard
- Faster convergence
- From 30 to 50 seconds to 6 seconds
- Backwards-compatible with 802.1D STP
- You can mix both in your network
- Very similar process
- An update, not a wholesale change