Connect 3 GS1920-24HP to USG-310.

dimensione_far Posts: 6  Freshman Member
edited April 14 in Switch
Hi all,
I own:
3 switches (layer 2, managed, 24 ports) model Zyxel GS1920-24HP;
1 router model Zyxel USG 310.

My network is segmented into 10 VLANs (1, 2, 3, 4, 5, 6, 7, 8, 10, 11), the central router routes packets between different VLANs (passing from an SPI firewall), from VLANs to Internet and vice versa (passing from an SPI firewall) and from VPNs to some resources on VLANs and Internet.
Each VLAN has a subnetmask of with netrange 192.168.X.0 / 24, where X is the VID specific to the VLAN, the router have always address 192.168.X.1 on each VLAN.

Switch1 is located in a second room, while the other 2 in the central rack, where the router is also located.

connected devices: VLAN5
switch management: VLAN1
network communication ports: 2 Gb in LAG

connected devices: VLAN2, VLAN3, VLAN4, VLAN6
switch management: VLAN1
network communication ports: 2 Gb in LAG

connected devices: VLAN1, VLAN5, VLAN7, VLAN8, VLAN10, VLAN11
switch management: VLAN1
network communication ports: 2 Gb in LAG

port1: bridge VDSL2 modem (PPPoE session to Internet)
port2: bridge VDSL2 modem (PPPoE session to Internet)
The 2 PPPoE sessions are independent and serve different VLANs.

The only VLANs that are replicated in multiple switches are:
VLAN1 which is used to manage the switches from their administration interfaces;
VLAN5 which has only 1 device not connected to the switch1 but to the switch3 (for logistic reasons of wiring).

I have two different connecting solutions:

switch1 LAG1 -> switch3 LAG1;
switch2 LAG1 -> switch3 LAG2;
switch3 LAG3 -> router LAG1.
Advantages: The router has on the LAG1 port the 10 VLAN interfaces and don't create VLANs interfaces replication.
Example) LAG1/1, LAG1/2, LAG1/3, LAG1/4, LAG1/5, LAG1/6, LAG1/7, LAG1/8, LAG1/10, LAG1/11
Disadvantages: This solution increase network traffic and latencies because if a VLAN2 device connects to a VLAN3 device the connection follow this flow:
switch2 -> switch3-> router -> switch3 -> switch2.

switch1 LAG1 -> router LAG1;
switch2 LAG1 -> router LAG2;
switch3 LAG1 -> router LAG3.
How can I configure the same VLANs on different LAG ports?
Example) LAG1/1, LAG1/5
LAG2/1, LAG2/2, LAG2/3, LAG2/4, LAG2/6
LAG3/1, LAG3/5, LAG3/7, LAG3/8, LAG3/10, LAG3/11

Which solution should be adopted?!


  • JasonTsai
    JasonTsai Posts: 104  Zyxel Employee
    Hi @dimensione_far,

    Welcome to Zyxel community!

    According to your description, I draw two topologies of your two solutions, please help me to verify if these are the same as you think. If not, please correct me or share your topology(with ports and VLAN) on the forum.

    For Solution 1, you just need to configure all VLANs and LAG on USG310 and Switches, then you may use it. If you have traffic concern, you may connect more than 2 cables(configure more than 2 port in a LAG) between two switches to have more bandwidth.

    For Solution 2, USG310 can't configure the same VLAN on different LAG ports.
    Therefore, I recommend you to use Solution 1.

    Solution 1:

    Solution 2:

    Hope it helps.

  • dimensione_far
    dimensione_far Posts: 6  Freshman Member
    Thanks for reply!
    My network topology is correct!
    With solution 2 what vlan id can i use for the devices administration?!
    Is convenient to have the same administration vlan for all 3 switches and router.
  • CrazyTacos
    CrazyTacos Posts: 53  Ally Member
    I wouldn't worry about latency. Switch latency are usually counted in units of microseconds (μs). Unless you have dozens of switches in tandem, there shouldn't be any noticeable difference between solution 1 and 2.
    Bandwidth and availability, on the other, is a different matter.
  • JasonTsai
    JasonTsai Posts: 104  Zyxel Employee
    Hi @dimensione_far,

    As I mentioned in the previous comment, I recommend you to use solution 1 because USG310 can't configure same VLAN on different LAG ports.

    If you still need to use solution 2 topology, the three LAG ports on the router need individual administrator VLAN and you will also have to configure correspond VLAN on the three switches.

    Hope it helps.