Saturday, February 20, 2016

STP

STP

 Edit 0 4
802.1d Bridge ID: Priority(2) + MAC(6)
System ID Expansion: Priority(4bits) + System ID(12bits) + MAC(6bytes)
  • PVST and 802.1s MST
Root Ports - hello's cost + local port cost
Originating Hello from root bridge have cost of 0

IEEE Costs


  • 10Mbps - 100
  • 100Mbps - 19
  • 1Gbps - 4
  • 10Gbps - 2

Designated Port Tiebreaker


  • Lowest bridge id
  • Lowest port priority
  • Lowest port number

Topology Change Notification (TCN) BPDU


  • Sends out root port until acknowledgment
  • Receives Topology Change Ack (TCA) BPDU
  • Root eventually receives TCN; TC flag set on nest Hello's from root

802.1d States


  • Blocking - stable
  • Listening - transitory
  • Learning - learn source mac; transitory
  • Forwarding - forward data frames; learn source mac; stable
  • Disabled - stable

Optimizing


PortFast


Access ports
Immediately forwarding states
Ignores listening and learning state

config# spanning-tree portfast default
config-if# spanning-tree portfast

UplinkFast


Access layer switches
Multiple uplinks to core switches
Replaces root-ports really fast when one goes down

config# spanning-tree uplinkfast [max-update-rate <rate>]

BackboneFast


Detect indirect link failures in network core
Queries switch when root-port stops receiving hellos
Root Link Query (RLQ) BPDU

config# spanning-tree backbonefast

Protecting


Root Guard


Ignored superior BPDUs, puts port into err-disabled state

BPDU Guard


Disabled upon any BPDUs, puts port into err-disabled state

UniDirectional Link Detection (UDLD)


When one of the two directions fails (usually fiber) a loop can occur.
Will auto come back up if Hellos received.
By default uses layer 2 messaging. When fails it falls into err-disabled state.

Aggressive Mode - Tries 8 times, if no response then both sides go into err-disabled

Loop Guard


When one of the two directions fails (usually fiber) a loop can occur.
Falls into loop-inconsistent state

No comments:

Post a Comment