STP chenshh Why STP? Computer Center, CS, NCTU 2 Computer - PowerPoint PPT Presentation

STP chenshh

Why STP? Computer Center, CS, NCTU 2

Computer Center, CS, NCTU Problems 1.Broadcast Storms 2.Mac-Table Inestability 3.Multiples copies of frames 3

Computer Center, CS, NCTU Basic STP (802.1d) Before we start we need talks about these 1.Bridge Protocol Data Unit(L2) 2.Bridge ID 4

Computer Center, CS, NCTU BPDU 1.L2 -> MAC Address 2.Sent to a specail multicast address 01:80:C2:00:00:00 5

Computer Center, CS, NCTU Bridge ID Generate by switch macs and its prioriy The default priority is 32768 6

Computer Center, CS, NCTU How STP works? 1.Root Bridge Election 2.Set port state 7

Computer Center, CS, NCTU Root Bridge Election Passing BPDUs,Choosing the smallest bridge id as root bridge. 8

Computer Center, CS, NCTU Set port role Three roles: Root port Designated port Block port 9

Computer Center, CS, NCTU Calculate Costs We want the cost to root be minimal! Set the right root port1 10

Setting states Computer Center, CS, NCTU 11

Setting states Computer Center, CS, NCTU 12

Computer Center, CS, NCTU Some tips Who is root is important! 13

Computer Center, CS, NCTU Some Issues 1.When changing states temporary cycles may appear. 2.Using timeouts is slow. 14

Computer Center, CS, NCTU Set port state Five States: Blocking Listening Learning Forwarding Disabled Each transitions between state cost several seconds Will not generate loops! 15

Computer Center, CS, NCTU RSTP (802.1w) Minify response time to several seconds Compatibility of STP 16

Computer Center, CS, NCTU More roles Root Designated Alternative Backup Disabled Edge 17

VLAN Issues Computer Center, CS, NCTU 18

Computer Center, CS, NCTU Cisco’s PVST One VLAN One STP 802.1q tagged modified BDPU 19

Computer Center, CS, NCTU Cisco’s PVST+ Run STP at VLAN 1 Run PVST at others Compatibility of STP/RSTP 20

Computer Center, CS, NCTU Cisco’s Rapid-PVST+ Add RSTP features 21

Computer Center, CS, NCTU Some Issues One VLAN -> One STP Hundreds VLAN -> Hundreds STP Massive PVST BPDUs on the networks Massive Calculations And these are cisco’s protocol not well supported on other manufacturers’ products 22

Computer Center, CS, NCTU MSTP MST Region MST Instance CIST 23

Computer Center, CS, NCTU MST Region Looks like a switch from outside 24

MST Instances Computer Center, CS, NCTU 25

Computer Center, CS, NCTU CIST CST & IST Common and Internal Spanning Tree Contacting multiple regions and compabiliy of STP/RSTP 26