Rapid Spanning Tree Protocol (RSTP) - How do trunk ports behave in RSTP ? Follow
Rapid Spanning Tree Protocol (RSTP) - How do trunk ports behave in RSTP ?
Trunk is a function that groups ports and combines the links among those ports into a single link.
As the scenario shown below, there are two links between SW1 and SW4 and therefore two loops:
1. Loop A: SW1, SW2, SW3 and SW4
2. Loop B: SW1 and SW4.
It causes problems such as a waste of CPU utilization if more than one loop exists. In order to prevent loop, Port 26 and 27 of SW1 and Port 26 and 28 of SW4 should be trunked as a group. In this way, two links between Switch 1 and 4 will be logically identified as one link by the system and only one loop exists with port 27 of SW3 blocked.
Use the following commands to enable LACP on port 26 and 27 of SW1.
SW_1#config
SW_1(config)#interface e 1/26
SW_1(config-if)#lacp
SW_1(config-if)#int e 1/27
SW_1(config-if)#lacp
Use the command "show interfaces status port-channel 1" to check trunk group members. As shown below, port 26 and 27 of SW1 are member ports of trunk group 1.
SW_1#show interfaces status port-channel 1
Information of Trunk 1
Basic Information:
Port Type : 1000BASE-T
MAC Address : 70-72-CF-58-F9-25
Configuration:
Name :
Port Admin : Up
Speed-duplex : Auto
Capabilities : 10half, 10full, 100half, 100full, 1000full
Broadcast Storm : Enabled
Broadcast Storm Limit : 64 Kbits/second
Multicast Storm : Disabled
Multicast Storm Limit : 64 Kbits/second
Unknown Unicast Storm : Disabled
Unknown Unicast Storm Limit : 64 Kbits/second
Flow Control : Disabled
VLAN Trunking : Disabled
Current Status:
Created By : LACP
Link Status : Up
Port Operation Status : Up
Operation Speed-duplex : 1000full
Up Time : 0w 0d 0h 3m 45s (225 seconds)
Flow Control Type : None
Max Frame Size : 1518 bytes (1522 bytes for tagged frames)
Member Ports : Eth1/26, Eth1/27
Use the command "show spanning-tree port-channel 1" to check information such as role and state of each port.
SW_1#show spanning-tree port-channel 1
Trunk 1 Information
---------------------------------------------------------------
Admin Status : Enabled
Role : Designate
State : Forwarding
Admin Path Cost : 0
Oper Path Cost : 2500
Priority : 128
Designated Cost : 0
Designated Port : 128.33
Designated Root : 4096.7072CF58F90B
Designated Bridge : 4096.7072CF58F90B
Forward Transitions : 24
Admin Edge Port : Auto
Oper Edge Port : Disabled
Admin Link Type : Auto
Oper Link Type : Point-to-point
Flooding Behavior : Enabled
Spanning-Tree Status : Enabled
Loopback Detection Status : Enabled
Loopback Detection Release Mode : Auto
Loopback Detection Trap : Disabled
Loopback Detection Action : Block
Root Guard Status : Disabled
BPDU Guard Status : Disabled
BPDU Guard Auto Recovery : Disabled
BPDU Guard Auto Recovery Interval : 300
BPDU Filter Status : Disabled
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