query on connecting a 3850 stack to N5K

[pokwan]

Hi,

We have a problem connecing a 3850 stack to a pair on N5K.  The N5Ks are connected to a pair of N7K. (diagram attached).

When the 3850 is connected, the one of the N5K (B) log shows that a loop was detected on one of the vlans (all VLANs are fine except 27). The mac address are below are the hardware address of the vlan interface.

%FWM-2-STM_LOOP_DETECT: Loops detected in the network for mac d867.d902.3c42 among ports Po10 and Po1 vlan 27 - Disabling dynamic learn notifications for 180 seconds

%FWM-2-STM_LOOP_DETECT: Loops detected in the network for mac 0000.0c9f.f0d9 among ports Po10 and Po1 vlan 27 - Disabling dynamic learn notifications for 180 seconds

The 3850 at the moment are not configured as an etherchannel to the N5K.

Can you advise?

TIA.

PF

[Philip D'Ath]

The ports where the 3850 and Nexus 5k connect - are they all configured the same?  For example, all are trunk ports with the same native VLAN?

[pokwan]

Phillip,

Thanks for the reply.

Yes they are configured the same, same native vlan.
It works fine if the interface to the 3580 on N5K A is disabled.  If the interface to the 3850 on N5K B is disabled, we still have the loop issue.

Will configuring a VPC from N5K to the 3850 help or cause any issue?

Thanks.

PF

[Philip D'Ath]

It's not a VPC but a Port-channel you need to configure, and as long as their is a VPC between the 5k's then that is a better solution.

The 3850 will need a corresponding Port-Channel configured as well.

[pokwan]

Phillip,

The config should be

N5K A
Int e1/25
 Channel-group 25 mode active

Int po 25
 Vpc 25

N5K B
Int e /25
 Channel-group 25 mode active

Int po 25
 Vpc 25

3850
Int te1/1/3
 Channel-group 25 mode active

Int te3/1/3
 Channel-group 25 mode active

If I didn’t have the vpc 25 on port-channel 25, the system will automatically create a random vpc id.
ie
Sh vpc
vPC status
----------------------------------------------------------------------------
id     Port        Status Consistency Reason                     Active vlans
------ ----------- ------ ----------- -------------------------- -----------
264064 Po1921      up     success     success                    2-4,6-15,13
                                                                 ,248,512....

Is the above not right?

Thanks.

PF

[Philip D'Ath]

The above looks good to me!

[pokwan]

Thanks Phillip.