Web and Unmanaged
Showing results for 
Search instead for 
Did you mean: 

Problem connecting two 1920 switches

Occasional Visitor

Problem connecting two 1920 switches


I have a weird problem connecting two 1920 switches with the following layout.

Default Vlan1 (all ports)
Gateway (firewall connected to port 28

Switch 2:
Vlan 1 : ip
Ports 1-16 untagged
Link from switch 1 connected to port 1

Vlan 2: ip
Ports 17-24 untagged
Gateway(firewall connected to port 28

Dhcp comes from each separate gateway. I don't want/need communication between vlans.

The problem is that as soon as I connect the cable between switches 1 and 2, I can't get an ip from dhcp or communicate even with a static ip on my pc, using vlan 1.

If I disconnect the cable and plug directly into switch one, there is no problem.

Vlan 2 is working well.

So far I added the gateway to each vlan.

Am i missing something?

Thanks in advance
Honored Contributor

Re: Problem connecting two 1920 switches

Hope not to be wrong but it smells like a loop.

Does the Firewall has two LAN ports: one Untagged (PVID 1) connected on port 28 of Switch 1 and the other one Untagged (PVID 2) connected on port 28 of Switch 2 or the Firewall uses just one single LAN port VLAN 1 Untagged plus VLAN 2 Tagged (sub-interface)?

Does the Switch 1 <--> Switch 2 uplink (single cable) permit all VLANs as when you define a Port Trunk between Switches?

Occasional Visitor

Re: Problem connecting two 1920 switches


Thanks for your reply.

The firewall has two separate ports for each of my switches. It is a fortigate 100D, divided into hardware switches, so no traffic can go between them. The weird thing is I have this same configuration on another lab here and it works without problem.

Regarding the switch link, it is between 2 access ports. Port 1 on switch 1 to port 2 on switch one. They are both untagged members on VLAN1.

Today I found the ARP table was being filled by the wireless network (VLAN so I disabled gratuitous ARP.

After that, I cleared the dynamic ARP.

Now the ARP table is moderate (about 50 addresses). But I'm still having the same problem between switches.


Honored Contributor

Re: Problem connecting two 1920 switches

Switch inter-link's ports should be set of Trunk type (not Access) IMHO.

Could you draw a basic network diagram reporting VLAN PVID, Untagged/Tagged ports status/configuration about all involved Switches/Firewall ports?

I've a similar setup: an old Fortinet FortiGate 100A providing two physically separated LANs interfaces as gateways for two different VLANs (Wired hosts group on VLAN id 1 and Wireless Guest hosts group on VLAN id 5), those Firewall's ports are connected to different ports (one PVID 1 the other PVID 5) of the same Switch, that Switch then has a Port Trunk (4x1Gbps) to another Switch (with all VLANs permitted).