Question about configuring stackwise switches (2 3850's)

[ronjonjonjon1]

I have 2 3850's that I am connecting together.  I am matching a configuration that exist in my datacenter on 2 3850's.  Below is how the interfaces are configured on the 2 switches:

interface Fo1/1/3

 stackwise-virtual dual-active-detection

interface Fo1/1/4

 stackwise-virtual link 1

My question:

1. Can I put the command 'stackwise-virtual link 1' on both ports to in effect make it a port-channel or do these commands have to be segregated for stackwise to work?  I don't know why it was initially configured this way, just trying to understand the relationship between these 2 commands.  Thanks.

[balaji.bandi]

what is oher device  you mean ? what model ?  if you lareayd have SWV domain, make sure you configure different domain number.

follow step by step guide :

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3850/software/release/16-6/configuration_guide/b_166_stck_mgr_ha_3850/b_166_stck_mgr_ha_3850_chapter_010.html

[Giuseppe Larosa · Accepted solution]

Hello @ronjonjonjon1,

follow the guide provided by BB

I agree that the forty GIGA links should be used for the SVL bundle in a port-channel .

it is a waste of resources to use a 40GE link for dual active detection.

You can use a direct link  between the two devices for dual active detection but it must be a separated link not part of the SVL port channel.

Hope to help

Giuseppe

[ronjonjonjon1]

Thanks for the response.  I ended up using 2 10G links between the 2 3850's.  Unfortunately, I don't have access to any 40G SFP molex cables, so that brings up 2 more questions.

Do I have to use a Cisco SFP-H10GB-CU3M Molex Cable with the SFP's already attached?  Or can I just use fiber with 10G SFP's?

Also, are you saying that the 'dual active detection' command is a waste because it acts as a failover link and "wastes" the 1 port unless there is an active switch fail?

[balaji.bandi]

if you have SFP then use Firbre patches.

[Giuseppe Larosa]

Hello @ronjonjonjon1 

you can use fiber pair with 10 GE SFP+ specially if they are SR short range you just need a pair of MM multi mode fiber.

>> are you saying that the 'dual active detection' command is a waste 

I just wanted to point out that on the dual active link only Fast Hellos are exchanged and this could be done even on a GE link.

There is not an high volume of traffic on this link.

The dual active link is highly recommended to be able to handle a fault scenario called dual active in case the SVL port channel fails the standby device will use the dual active detection to decide what to do: if the primary is alive the standby chassis will shut down its ports to avoid traffic to be sent to it when there is no user data path between the two devices. if the primary is not alive on the dual active detection link and the SVL port channel has failed,  the standby chassis will promote itself as master and will keep all its ports alive in an attempt to provide some connectivity.

To be noted you can have up to 4 different dual-active links between the two devices.

Hope to help

Giuseppe