Cisco CBS-350 uplink port goes up and down

RumenB · ‎03-20-2023

Hi there,

I have the following problem.

The switch is CBS350-24T-4X - CBS350. There are several trunk ports with other cisco switches (SF-300 series). There all works OK. Tagging, untagging and so on.

The problem comes with connection with one unmanaged non cisco switch. The switch works like expected but when I try to uplink it to any of the ports of CBS350, the link goes up and down every few seconds. No difference when changing ports or cables.

Can anybody suggest where is the problem?

marce1000 · ‎03-20-2023

- Check logs on CBS350 when this happens,

M.

-- Each morning when I wake up and look into the mirror I always say ' Why am I so brilliant ? '
When the mirror will then always repond to me with ' The only thing that exceeds your brilliance is your beauty! '

pieterh · ‎03-20-2023

as this unknown switch is an unmanaged switch, it will have NO knowledge of VLAN's
1) configure the connected port as an access-port (one vlan untagged, NO tagged vlans)
2) configure one of your switches as a spanning-tree root for this vlan (increase the priority)
so spanning-tree will not alter when you attach this unmanaged switch
3) block incoming BPDU's on this port