show vpc consistency-parameters
Displays the consistency parameters for vPC links, ensuring that both peer switches have identical configurations to prevent traffic disruption.
Overview
The 'show vpc consistency-parameters' command is a critical troubleshooting tool for verifying that vPC peer switches have identical configurations for parameters that affect the vPC domain. In Cisco NX-OS, vPC (Virtual Port Channel) allows a single logical link to be formed across two physical switches, providing redundancy and increased bandwidth. For vPC to function correctly, both peer switches must agree on certain parameters; otherwise, traffic loops or black holes can occur. This command displays both Type 1 and Type 2 parameters. Type 1 parameters are mandatory to match; if they differ, the vPC is suspended to protect the network. Type 2 parameters are informational and do not cause suspension but should be aligned for optimal operation. The command can be used in EXEC mode with optional keywords 'global' to show system-wide parameters or 'interface <port-channel>' to show per-interface parameters. It is essential during initial vPC setup, after configuration changes, and when troubleshooting vPC instability. On Nexus platforms, this command is the primary method to detect configuration drift between peers.
show vpc consistency-parameters [global | interface <interface-type> <interface-number>]When to Use This Command
- Verify that vPC peer switches have matching STP, VLAN, and interface parameters to avoid Type-1 inconsistencies.
- Troubleshoot vPC member link failures caused by mismatched port channel configurations.
- Validate consistency after making configuration changes on one vPC peer.
- Check global parameters like MAC address aging timer and QoS settings across vPC peers.
Parameters
| Parameter | Syntax | Description |
|---|---|---|
| global | global | Displays global consistency parameters that apply to the entire vPC domain, such as STP mode, VLAN allowed on peer-link, and MAC aging timer. |
| interface | interface <interface-type> <interface-number> | Displays consistency parameters for a specific vPC member interface (port-channel). The interface type is typically 'port-channel' and the number is the channel group ID. |
Command Examples
Check global vPC consistency parameters
show vpc consistency-parameters globalGlobal Consistency Parameters:
Parameters that must be consistent across all vPC interfaces:
Type 1 Parameters:
vPC keep-alive status : up
vPC peer-link status : up
STP Mode : Rapid-PVST
STP Domain : 1
VLANs allowed on peer-link : 1-100,200
VLANs active on peer-link : 1-100,200
MAC aging timer (sec) : 1800
QoS (trust type) : trust-cos
MTU : 1500
LACP mode : active
LACP rate : fast
LACP system priority : 32768
LACP system ID : 00:00:00:00:00:01
Type 2 Parameters:
STP Root Bridge : 32768.aaaa.bbbb.cccc
STP Root Port : Eth1/1
STP Root Cost : 4The output shows global parameters that must match on both vPC peers. Type 1 parameters (e.g., STP mode, VLAN allowed) cause vPC to suspend if mismatched. Type 2 parameters (e.g., STP root bridge) are informational and do not cause suspension.
Check consistency for a specific vPC member interface
show vpc consistency-parameters interface port-channel 10Interface port-channel10:
Type 1 Parameters:
vPC interface ID : 10
STP Port Type : edge
STP Port Guard : root
STP Port Priority : 128
STP Port Path Cost : 4
Allowed VLANs : 1-100,200
Active VLANs : 1-100,200
Native VLAN : 1
MTU : 1500
Admin port mode : trunk
Operational port mode : trunk
Admin port speed : auto
Operational port speed : 10000
Admin port duplex : auto
Operational port duplex : full
Port Channel Mode : active
Port Channel Load-balance : src-dst-ip
Type 2 Parameters:
STP Port State : forwarding
STP Port Role : designatedThis output shows per-interface consistency parameters. Type 1 mismatches (e.g., allowed VLANs, native VLAN) will cause the vPC to be suspended. Type 2 mismatches are logged but do not affect vPC operation.
Understanding the Output
The output is divided into Type 1 and Type 2 parameters. Type 1 parameters are critical: if they differ between vPC peers, the vPC will be suspended to prevent loops or traffic black-holing. Examples include STP mode, VLAN allowed on peer-link, MTU, and LACP settings. Type 2 parameters are informational and do not cause suspension, but mismatches may indicate configuration drift that could lead to suboptimal behavior. The 'global' view shows system-wide parameters, while the interface view shows per-port-channel settings. Healthy output shows identical values on both peers for Type 1 parameters. Problem values appear when a mismatch is detected; the vPC will be suspended and an error message logged.
Configuration Scenarios
Initial vPC Setup Verification
After configuring vPC on two Nexus switches, verify that all Type 1 parameters match before bringing the vPC up.
Topology
Nexus-A --- peer-link --- Nexus-B
| |
+---- vPC member link ---+Steps
- 1.Configure vPC domain, peer-keepalive, and peer-link on both switches.
- 2.Configure vPC member port-channels on both switches.
- 3.Run 'show vpc consistency-parameters global' on both switches and compare.
- 4.Run 'show vpc consistency-parameters interface port-channel <id>' on both switches and compare.
! On both switches: vpc domain 10 role priority 100 peer-keepalive destination 10.1.1.2 source 10.1.1.1 peer-gateway auto-recovery interface port-channel 10 switchport mode trunk vpc 10 interface Ethernet1/1 channel-group 10 mode active
Verify: Ensure that 'show vpc consistency-parameters' shows identical Type 1 values on both peers. If mismatches exist, correct them before proceeding.
Watch out: A common catch is forgetting to set the same STP mode or VLAN allowed list on both peers, which will cause vPC suspension.
Troubleshooting with This Command
When a vPC is suspended or not coming up, the first step is to run 'show vpc consistency-parameters' on both peers. Look for Type 1 parameters that differ. Common mismatches include: STP mode (e.g., one peer running Rapid-PVST while the other runs MST), allowed VLANs on the peer-link, native VLAN, MTU, LACP mode, and port channel load-balancing algorithm. If a mismatch is found, correct the configuration on the offending switch. For example, if the allowed VLAN list differs, update the peer-link or member interface to match. If the mismatch is on a global parameter, adjust the vpc domain configuration. After correction, the vPC should automatically recover. If the vPC remains suspended, check 'show vpc' for error messages. Also verify that the peer-keepalive link is up and the peer-link is operational. Type 2 mismatches can be ignored but may indicate configuration drift that should be addressed for consistency. In NX-OS, the command also helps identify issues with LACP settings; ensure both peers use the same LACP mode (active/passive) and system priority.
CCNA Exam Tips
Remember that Type 1 mismatches cause vPC to suspend; Type 2 do not.
On the CCNP exam, know that 'show vpc consistency-parameters' is the primary command to verify vPC configuration alignment.
Be aware that some parameters like STP root bridge are Type 2 and not critical for vPC operation.
Common Mistakes
Assuming all mismatches cause vPC suspension; only Type 1 parameters matter.
Forgetting to check global parameters when troubleshooting vPC issues.
Not verifying consistency after making changes on only one peer.
Platform Notes
On Cisco NX-OS, the 'show vpc consistency-parameters' command is more detailed than on Cisco IOS (where vPC is not available). It includes both global and interface-specific parameters. The output is divided into Type 1 and Type 2, which is a Nexus-specific classification. In contrast, on Cisco IOS with Virtual Switching System (VSS), consistency checks are done via 'show switch virtual consistency'. On Nexus, the command is essential for vPC troubleshooting. Version differences: In earlier NX-OS versions, some parameters like 'LACP system priority' might not be displayed; newer versions include them. Always ensure both peers run the same NX-OS version to avoid unexpected mismatches.
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