[PLUG] OT VLAN Setup between 2 Cisco switches

[Mike C.]

>
> The two switches talk just fine between the two devices on
> VLAN 1.
>

Yes, because the default / admin VLAN 1 is automagicaly extended across
switches for obvious reasons.


> But VLAN 2 will not talk.


VLANs are broadcast domains, and with the exception of the default/admin
VLAN 1, unless you extend the vlan broadcast domain intentionally, vlan
traffic stays local to the switch.



> The interesting thing is that if Iunplug the SFP transceiver in port 49
> (associated with VLAN 1) then VLAN 2 will start to talk to the other switch
> over the SFP device in port 50.
>

This is the Spanning Tree Protocol unlblockiing and finding a new route
after a link failure.


> I am assuming configuration somewhere but not sure where.
>

Correct assumption. You need to configure a vlan trunk for VLAN 2 to
traverse the fiber links between the 2 switches,

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3850/software/release/3se/vlan/configuration_guide/b_vlan_3se_3850_cg/b_vlan_3se_3850_cg_chapter_0110.pdf