CCIE Routing & Switching v5 Workbook -
CCIE R&S v5 Advanced Technology Labs -
LAN Switching
MST and Rapid Spanning Tree
A Note On Section Initial Configuration Files: You must load the
initial configuration files for the section, named LAN Switching Initial
Spanning Tree, which can be found in
. Reference the Virtual Routers &
Physical Switches Diagram to complete this task.
Task
Configure Multiple Spanning-Tree on SW1 - SW4 as follows:
Use region named MST and a revision of 1.
Instance 1 should service VLANs 1 - 100.
Instance 2 should service VLANs 101 - 200.
Configure PortFast on SW1’s FastEthernet0/1 so that it immediately begins
forwarding when enabled.
Configuration
SW1 - SW4:
spanning-tree mst configuration
name MST1
revision 1
instance 1 vlan 1-100
instance 2 vlan 101-200
!
spanning-tree mode mst
SW1:
interface FastEthernet0/1
spanning-tree portfast
Verification
When MST is enabled, Rapid Spanning-Tree Protocol (RSTP) is automatically
enabled. RSTP is an IEEE standard defined in 802.1w that speeds up convergence
through a reliable handshaking process. RSTP defines new port roles to
automatically allow for the functionality built into Cisco proprietary features such as
PortFast and UplinkFast.
RSTP Edge ports behave the same as PVST PortFast-enabled ports. However, to
maintain backward-compatible configurations, Cisco’s implementation of RSTP
does not automatically elect edge ports as the standard suggests. Instead, a port
must be configured as an edge port with the
spanning-tree portfast
command:
SW1#show spanning-tree interface fastEthernet0/1
Mst InstanceRole Sts CostPrio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
MST0Desg FWD 200000
128.3P2p Edge
MST1Desg FWD 200000
128.3P2p Edge
!
!SW1#show spanning-tree mst interface fastEthernet0/1
FastEthernet0/1 of MST0 is designated forwarding Edge port: edge(enable)
port guard : none
(default)
Link type: point-to-point (auto)
bpdu filter: disable
(default)
Boundary : internal
bpdu guard : disable
(default)
Bpdus sent 2954, received 0
Instance Role Sts CostPrio.Nbr Vlans mapped
-------- ---- --- --------- -------- -------------------------------
0Desg FWD 200000128.3none
1Desg FWD 200000128.31-100
!
!SW1#show spanning-tree interface fastEthernet0/1 portfast
MST0enabled
MST1enabled
If there were a device connected to FastEthernet0/1 such as a hypervisor that could
tag frames with dot1q tags, we could configure this port as a trunk port and also
configure it as an Edge port. This will ensure that it immediately begins forwarding
when enabled for all VLANs being trunked:
SW1#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.SW1(config)#interface FastEthernet0/1
SW1(config-if)#switchport trunk encapsulation dot1q
SW1(config-if)#switchport mode trunk
SW1(config-if)#spanning-tree portfast trunk
%Warning: portfast should only be enabled on ports connected to a single
host. Connecting hubs, concentrators, switches, bridges, etc... to this
interface when portfast is enabled, can cause temporary bridging loops.
Use with CAUTION
!
!SW1#show spanning-tree interface fastEthernet0/1
Mst InstanceRole Sts CostPrio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
MST0Desg FWD 200000
128.3P2p Edge
MST1Desg FWD 200000
128.3P2p Edge
MST2Desg FWD 200000
128.3P2p Edge
!
!SW1#show spanning-tree mst interface fastEthernet0/1
FastEthernet0/1 of MST0 is designated forwarding Edge port: edge(trunk)
port guard : none
(default)
Link type: point-to-point (auto)
bpdu filter: disable
(default)
Boundary : internal
bpdu guard : disable
(default)
Bpdus sent 9, received 0
Instance Role Sts CostPrio.Nbr Vlans mapped
-------- ---- --- --------- -------- -------------------------------
0Desg FWD 200000128.3none
1Desg FWD 200000128.31-100
2Desg FWD 200000128.3101-200
!
!SW1#show spanning-tree interface fastEthernet0/1 portfast
MST0enabled
MST1enabled
MST2enabled