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vPC Status Down between Nexus 5000 and Directly connected Server

 

 

Introduction


This document describes a scenario where two Nexus 5000 connecting to a single server with vPC do not transition to vPC active state and remain in down state. A pair of switches acting as a vPC peer endpoint look like a single logical entity to port-channel attached devices; the two devices that act as the logical port-channel endpoint are actually two separate devices. This setup has the benefits of hardware redundancy combined with the benefits offered by port-channel, e.g loop management.

 

 

 

Virtual Port Channel (vPC)

 

A virtual PortChannel (vPC) allows links that are physically connected to two different Cisco Nexus™ 5000 Series devices to appear as a single PortChannel to a third device. The third device can be a Cisco Nexus 2000 Series Fabric Extender or a switch, server, or any other networking device. The vPC domain includes both vPC peer devices, the vPC peer keepalive link, the vPC peer link, and all the PortChannels in the vPC domain connected to the downstream device. You can have only one vPC domain ID on each device.

 

 

Topology

 

 

vPC Configuration

 

Nexus 5k1
int eth 1/12
channel-group 204 mode active
!
interface port-channel204
  switchport access vlan 1072
  speed 10000
  vpc 204
!

Nexus 5k2
interface port-channel204
  switchport access vlan 1072
  speed 10000
  vpc 204
!
interface Ethernet1/12
  channel-group 204 mode active
!

 

 

Description


The vPC peer is shown alive and vPC adjancency is also formed, but the vPC status is down on both switches.

 

5k1# show port-channel summary
Flags:  D - Down        P - Up in port-channel (members)
        I - Individual  H - Hot-standby (LACP only)
        s - Suspended   r - Module-removed
        S - Switched    R - Routed
        U - Up (port-channel)
        M - Not in use. Min-links not met

--------------------------------------------------------------------------------
Group Port-       Type     Protocol  Member Ports
     Channel
-------------------------------------------------------------------------------
1     Po1(SU)     Eth      NONE      Eth1/31(P)
204   Po204(SD)   Eth      LACP      Eth1/12(I)
!

5k1# show vpc br
Legend:
                (*) - local vPC is down, forwarding via vPC peer-link
vPC domain id                   : 5  
Peer status                     : peer adjacency formed ok     
vPC keep-alive status           : peer is alive                
Configuration consistency status: success
Per-vlan consistency status     : success                      
Type-2 consistency status       : success
vPC role                        : secondary                    
Number of vPCs configured       : 9  
Peer Gateway                    : Disabled
Dual-active excluded VLANs      : -
Graceful Consistency Check      : Enabled
vPC Peer-link status
---------------------------------------------------------------------
id   Port   Status Active vlans   
--   ----   ------ --------------------------------------------------
1    Po1    up     1-9,33,36,43,46,329,1050-1059,1070,1072-1073,1101-      
                   1116,1997                                               
vPC status
----------------------------------------------------------------------------
id     Port        Status Consistency Reason                     Active vlans
------ ----------- ------ ----------- -------------------------- -----------                    
204    Po204       down*  success     success                    -    


5k2# show port-channel summary
Flags:  D - Down        P - Up in port-channel (members)
        I - Individual  H - Hot-standby (LACP only)
        s - Suspended   r - Module-removed
        S - Switched    R - Routed
        U - Up (port-channel)
        M - Not in use. Min-links not met
--------------------------------------------------------------------------------
Group Port-       Type     Protocol  Member Ports
      Channel
--------------------------------------------------------------------------------
1     Po1(SU)     Eth      NONE      Eth1/32(P)  
204   Po204(SD)   Eth      LACP      Eth1/12(I)  
!

5k2# show vpc brief
Legend:
                (*) - local vPC is down, forwarding via vPC peer-link
vPC domain id                   : 5  
Peer status                     : peer adjacency formed ok     
vPC keep-alive status           : peer is alive                
Configuration consistency status: success
Per-vlan consistency status     : success                      
Type-2 consistency status       : success
vPC role                        : primary                      
Number of vPCs configured       : 41
Peer Gateway                    : Disabled
Dual-active excluded VLANs      : -
Graceful Consistency Check      : Enabled
vPC Peer-link status
---------------------------------------------------------------------
id   Port   Status Active vlans   
--   ----   ------ --------------------------------------------------
1    Po1    up     1-9,33,36,43,46,329,1050-1059,1070,1072-1073,1101-      
                   1116,1997                                               
vPC status
----------------------------------------------------------------------------
id     Port        Status Consistency Reason                     Active vlans
------ ----------- ------ ----------- -------------------------- -----------                               
204    Po204       down*  Not         Consistency Check Not      -          
                          Applicable  Performed        

 

 

Explanation


The Link Aggregate protocol configured above is what's referred to as dynamic, and as such it will use the Link Aggregation Control Protocol (LACP) to negotiate with the link partner i.e., the server, on a number of parameters to use for the forming and control of the aggregate.

 

What can be seen from the show port-channel summary command is that the links are in the Individual (I) state. This is usually an indication that the remote device is not sending LACPDU frames. We can see this by checking the Recv column in the output of show lacp counters interface port-channel 204 command. It will most likely be 0 or some small static value which wont change even after bouncing the port channel.

If that's the case check with the server how it has the aggregate configured. It must be using NIC teaming software supporting something along the lines of IEEE 802.3ad Dynamic (HP), IEEE 802.3ad or mode=4 (Linux) or LACP with VMware ESXi.

If you're connecting to a server whose OS only supports static link aggregation e.g., VMware ESXi prior to version 5.1, then you should change the Nexus configuration to use static Link Aggregation with the channel-group 204 mode on command under the Ethernet1/12 interface. Note that you can't change the keywords used with the channel-group command, but have to remove it and add it back using the on keyword.

This document is based on following discussion

https://supportforums.cisco.com/discussion/12036211/force-consistency-check

 

 

Related Information


Quick Start Guide :: Virtual Port Channel (vPC)
vPC Best Practices for Nexus 7000 and 5000

 

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