How To Connect 2 Switch Stacks Over Ethernet?

[N3TWORK3D]

Hi,

I have 2 switch stacks (2 3850s in each), on different floors.

What is the best way to connect them and how do I properly configure the ports?

If Ethernet, can I bond the ports to provide more throughput? What about cross over cable?

Thanks!

[Predrag Jovic · Accepted solution]

Create etherchannel between switches (one link from each switch).

Stack 1

interface range Gi1/0/49, Gi2/0/49

 shutdown

 switchport mode trunk

 channel-group 1 mode active

 no shutdown

Stack 2

interface range Gi1/0/49, Gi2/0/49

 shutdown

 switchport mode trunk

 channel-group 1 mode active

 no shutdown

Generally you can, but don't have to use crossover cables. Auto-MDIX is default on Cisco devices (except for SFP -SX and -LX  module interfaces).

[N3TWORK3D]

Awesome! Thanks for the quick response.

Can you tell me though what 1/0/49 is? My switch is only goes up to 1/0/48 or is that just a way to say any port?

[Predrag Jovic]

You're welcome.

On 48 port switch Gi1/0/49-52 are typically SFP uplink ports (fiber or copper connection, can have 10Gb ports, on 3850 models uplink module is not built in).

3850 architecture details:

Cisco Catalyst 3850 Series - Switches StackWise - 480 Architecture

on Cisco live (need to have account there  (but, it is free registration)):

Cisco Catalyst 3850 and 3650 Switching Architecture

[N3TWORK3D]

Oh gotcha. I actually have them as 1/1/1-4 and 2/1/1-4

So then are you suggesting that I only use the SFP uplink ports? I do not have those adapters. I am curious if I can use one port from each switch in the stack to create the EtherChannel over to the other switch stack.

Thanks.

[Predrag Jovic]

It is general recommendation to use uplink ports.

And, yes, you can create ehterchannel from different stack switches to other devices (and it is, most of the time, recommended to do so).

[Joseph W. Doherty]

As also noted by Predrag, yes you can use regular copper ports both in Etherchannels and to interconnect switches. Cannot say for certain for a 3850, but on the earlier 3750 series, Cisco had 2 MB RAM buffers per 24 copper ports or for its module ports. I.e. module ports might have more and/or better hardware resources backing them because they are most often used for uplinks and often carry more traffic than copper edge ports.

Predrag also showed using your Etherchannel as a L2 trunk, but since a 3850 is a L3 switch, you should also have the option to use a Etherchannel as a L3 link too.

Lastly, I don't know what the default load balancing hashing algorithm is for a 3850, but you might want to confirm, if more than one algorithm is available, you're using the optimal algorithm for your traffic.