Cisco NX-OS/IOS STP Comparison
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* Typically the core/backbone devices should be configured as the primary and secondary root bridges. | * Typically the core/backbone devices should be configured as the primary and secondary root bridges. | ||
* The default bridge priority is 32,768 (plus the VLAN #). The lower the value, the more likely it will become the root bridge. | * The default bridge priority is 32,768 (plus the VLAN #). The lower the value, the more likely it will become the root bridge. | ||
| - | * Configure 802.1q trunk ports as '''edge trunk''' port type when connecting to | + | * Configure 802.1q trunk ports as '''edge trunk''' port type when connecting to layer-3 hosts such as firewalls, load-balancers, or servers for faster convergence. |
Revision as of 06:23, 22 January 2011
Objective
This tech note outlines the main differences in Spanning-Tree Protocol (STP) support between Cisco® NX-OS Software and Cisco IOS® Software. Sample configurations are included for Cisco NX-OS and Cisco IOS Software for some common features to demonstrate the similarities and differences. Please refer to the NX-OS documentation on Cisco.com for a complete list of supported features.
STP Overview
STP is a standards based link-layer protocol originally defined in IEEE 802.1d that runs on switches to prevent forwarding loops when using redundant layer-2 network topologies. Newer variants of STP have been developed called Rapid Spanning Tree protocol (RSTP) defined in IEEE 802.1w and Multiple Spanning Tree protocol (MST) defined in IEEE 802.1s that are enhanced for better scalability and converge faster than the original version.
Important Cisco NX-OS and Cisco IOS Software Differences
In Cisco NX-OS:
- STP supports stateful process restarts and In-Service-Software-Upgrades (ISSU) if two supervisors are present in a chassis.
- Rapid-PVST+ and the MST protocols are supported.
- Rapid-PVST+ is enabled by default.
- VLANs 3968-4047,4094 are reserved for internal use. Cisco IOS Software reserves VLANs 1002-1005,4095 for internal use by default.
- The STP extended system-id is always enabled. Cisco IOS software requires the global spanning-tree extend system-id configuration command.
- The STP port types are identified with the port type designation as opposed to the portfast designation in Cisco IOS Software.
Things You Should Know
The following list provides some additional facts about the Cisco NX-OS that should be helpful when designing, configuring, and maintaining a network configured with the STP.
- Rapid-PVST+ is interoperable with the 802.1d STP.
- Rapid-PVST+ is interoperable with MST. (Enabled by default)
- Only one STP can be enabled per VDC.
- Bridge Assurance is enabled globally by default, but is disabled on an interface by default.
- Bridge Assurance can be enabled for an interface using the spanning-tree port type network interface command.
- The clear spanning-tree counters command clears the counters for an STP interface or a VLAN.
- STP enhancements such as BPDU Guard, Loop Guard, Root Guard, and BPDU Filtering are supported.
Spanning-Tree best practices are applicable to both Cisco NX-OS and Cisco IOS Software
- Do not disable STP. Even if the layer-2 topology does not require STP, it should always be enabled as a safeguard for configuration and/or cabling errors.
- Changing the STP mode can disrupt traffic.
- Enabling Bridge Assurance is recommended. However, only enable Bridge Assurance on layer-2 links if both devices on each end of the link support it.
- Typically the core/backbone devices should be configured as the primary and secondary root bridges.
- The default bridge priority is 32,768 (plus the VLAN #). The lower the value, the more likely it will become the root bridge.
- Configure 802.1q trunk ports as edge trunk port type when connecting to layer-3 hosts such as firewalls, load-balancers, or servers for faster convergence.
Configuration Comparison
The following sample code shows configuration similarities and differences between the Cisco NX-OS and Cisco IOS Software CLIs. The CLI is identical with the exception of the port type terminology. The Cisco IOS uses the portfast designation, whereas Cisco NX-OS uses the port type designation.
| Cisco IOS CLI | Cisco NX-OS CLI | |
|---|---|---|
| Configuring VLANs |
| vlan 10,20 | vlan 10,20 |
|---|
| Configuring Rapid PVST+ |
| spanning-tree mode rapid-pvst | Rapid-PVST is enabled by default.
|
|---|
| Configuring the Rapid-PVST+ Bridge Priority |
| spanning-tree vlan 10 root primary
spanning-tree vlan 20 root secondary | spanning-tree vlan 10 root primary
spanning-tree vlan 20 root secondary |
|---|
| Configuring MST |
| spanning-tree mode mst | spanning-tree mode mst |
|---|
| Configuring a MST Instance |
| spanning-tree mst configuration
instance 1 vlan 10 instance 2 vlan 20 | spanning-tree mst configuration
instance 1 vlan 10 instance 2 vlan 20 |
|---|
| Configuring the MST Bridge Priority |
| spanning-tree mst 1 root primary
spanning-tree mst 2 root secondary | spanning-tree mst 1 root primary
spanning-tree mst 2 root secondary |
|---|
| Configuring STP Port Types Globally |
| spanning-tree portfast edge default
or spanning-tree portfast network default | spanning-tree port type edge default
or spanning-tree port type network default |
|---|
| Configuring STP Port Types per Interface |
| interface gigabitethernet1/1
switchport spanning-tree portfast edge or spanning-tree portfast network or spanning-tree portfast disable | interface ethernet 1/1
switchport spanning-tree port type edge or spanning-tree port type network or spanning-tree port type normal |
|---|
| Configuring a Trunk as an Edge Port Type |
| interface gigabitethernet1/1
switchport spanning-tree portfast edge trunk | interface ethernet 1/1
switchport spanning-tree port type edge trunk |
|---|
| Disabling PVST Simulation Globally |
| no spanning-tree mst simulate pvst global | no spanning-tree mst simulate pvst global |
|---|
| Disabling PVST Simulation per Port |
| interface gigabitethernet1/1
switchport spanning-tree mst simulate pvst disable | interface ethernet 1/1
switchport spanning-tree mst simulate pvst disable |
|---|
Verification Command Comparison
The following table lists some useful show commands for verifying and troubleshooting a STP network configuration. The show commands are almost identical for Cisco IOS and Cisco NX-OS Software.
| Cisco NX-OS STP | Cisco IOS Software STP | Command Description |
|---|---|---|
| show spanning-tree | show spanning-tree | Displays high level process information for all STP enabled VLANs |
| show spanning-tree active | show spanning-tree active | Displays all ports in an active state |
| show spanning-tree blockedports | show spanning-tree blockedports | Displays all ports in a blocked state |
| show spanning-tree detail | show spanning-tree detail | Displays detailed information per STP instance |
| show spanning-tree inconsistentports | show spanning-tree inconsistentports | Displays inconsistent port status |
| show spanning-tree interface <type> | show spanning-tree interface <type> | Displays detailed STP information for a specific interface (many sub-options) |
| show spanning-tree mst | show spanning-tree mst | Displays high-level MST configuration |
| show spanning-tree mst configuration | show spanning-tree mst configuration | Displays the MST instance configuration |
| show spanning-tree mst detail | show spanning-tree mst detail | Displays detailed MST information |
| show spanning-tree mst interface | show spanning-tree mst interface | Displays MST interface information |
| show spanning-tree pathcost method | - | Displays STP path cost method |
| show spanning-tree root | show spanning-tree root | Displays STP root information |
| show spanning-tree summary | show spanning-tree summary | Displays STP summary information |
| show spanning-tree vlan <#> | show spanning-tree vlan <#> | Displays per VLAN STP information |
