# Best way to configure layer 2 daisy chain with 2 layer 3 switches/gateways at either end?

I would like to implement a linear daisy chain for the purpose of transmitting internet over a considerable distance.

One motivation behind the use of a linear daisy chain for this problem is that each point acts as a repeater. It is not possible, due to range and distance, to connect a point that is not adjacent to the Layer 3 switch, directly using a cable. So, the daisy chain acts to repeat the signal.

I also have 3 different cables for implementing this. The motivation behind 3 cables is to triple the bandwidth. I would like to evenly distribute the bandwidth of these 3 cables across the points. However, as mentioned above, each of the 3 cables must be present at each point for the signal to be retransmitted and to be able to go the distance.

Since there are two layer 3 switches/gateways at either end, I would like to make sure I utilize the internet bandwidth available at both sides. These two layer 3 switches interface with separate networks that go to the internet.

The way I was planning on achieving what I am describing above is by using VLANs. For example, Gateway #1 cable 1 would be VLAN1, G#1 Cable 2 would be VLAN2, G#1 Cable 3 would be VLAN3, Gateway #2 cable 1 would be VLAN4 etc. up to VLAN6.

Then, I would be able to drop a "fraction" of a cable's bandwidth at a particular point by assigning one of the 6 VLANs. Each VLAN would be available at each point, regardless of how far it is from the other Layer 3 switch supplying the VLAN, because of how the cable is continuous between each point and both of the Layer 3 switches.

Each point would be a Layer 2 managed switch.

Another benefit is that I would be able to manually adjust at any time which point gets served by which "internet channel" or VLAN.

Here is a simple diagram : https://ibb.co/6cKVpYx. There could be even more points then depicted. For example, there could be 12 points, and then I would like the 6 cables carrying 6 Gbps to be evenly divided, such that each of the 6 VLAN "Cable or Channel" is assigned to 2 points.

I was concerned about loops. But then again, I am only utilizing one VLAN per point, so I wasn't too sure how much of a problem loops would be. I was also thinking about port aggregation.

Are there any problems with this implementation? Should I be doing something differently to make it work?

Essentially, I just want an effective way of carrying traffic point-to-point and distributing the traffic effectively and evenly across those points with what is available with those 3 wires, 2 layer 3 switch/gateways, and layer 2 switch points.

Bonus points for this design would be the ability to failover automatically to a different Gateways VLAN. If you could point me in the right direction for that, then that would be very appreciated. So for example, if Point 2 is on VLAN 2 of Gateway #1, but Gateway #1 goes down, then I would want it to be on one of Gateway #2's VLANs to be able to continue to communicate.

The bandwidth at either end is 10Gbps. For this reason, those 3 cables would not exceed the available bandwidth, making it worthwhile.

Note : Different hardware or fiber links etc. are not options. The factors I have discussed above cannot be modified and are firm constraints.

I'll be running Ubquiti equipment.

Edit

So I am thinking of the following final solution:

• Active-Active VRRP for load sharing. This would involve 2 VRRP groups. One for Layer 3 Switch #1 Master and one for Layer 3 Switch #2 Master.
• Port or Link Aggregation that would combine the 3 cables into one. This results in additive bandwidth as intended. This way I can carry the signal through each point for signal regeneration and also maintain maximum bandwidth. This is also to prevent any possibility of loops. Makes life easier.
• Each point will be on a separate VLAN. In this way, I am able to assign which Gateway I want it to use. Thanks to VRRP, this would also mean that it would automatically switch to the other Gateway if one of the Gateways were to go down.
• What is your bandwidth to the Internet at each end? What is the bandwidth of each link between the switches? You may not need all that bandwidth if your Internet links are not huge. Also, you might consider link aggregation (etherchannel in Cisco lingo) as a simpler way of getting more bandwidth. Jan 28, 2022 at 16:35
• It would be about 10 Gbps at either end. For this reason, the 3 cables would not exceed the available bandwidth and would be a useful way to increase speed. The bandwidth between the switches is based on the 3 cables (see diagram). It would be 3Gbps as well. So just port aggregation across each one? But how would that work with 2 layer gateway switches?
– Doug
Jan 28, 2022 at 16:38
• You don't need separate VLANs for this. One VLAN will suffice. You may want multiple VLANs however for other reasons. Jan 28, 2022 at 19:26
• Okay thanks. I wanted separate VLANs for the purpose of containerizing the points. I understand what you mean though. I could just set half of the devices on one VRRP IP and the other half on the other one, right? Otherwise, do you think my final bullet points are solid for this setup?
– Doug
Jan 28, 2022 at 19:27
• Other than the point about VLANs, I would agree. Jan 28, 2022 at 20:33

## 2 Answers

One way to get more bandwidth without having to manage lots of VLANs is to use link aggregation (i.e. etherchannel) between each device. The three (or more) links between the switches act as a single logical link and data is distributed among the links (per flow), effectively combining the bandwidth of the links.

You can use a First Hop Redundancy Protocol (HSRP, GLBP or VRRP) to allow hosts to use either gateway if available. You can also load share between the gateways, effectively doubling your bandwidth.

• Thanks. That is an excellent point. One of the primary concerns I had with aggregation and other methods, is load sharing exactly as you mentioned. There is 3 Gbps available from both of the Gateways. My total internet throughput could be 6 Gbps. So with aggergation, I understand that if I have 3 cables, I can combine it to form 3Gbps and use that in the Daisy Chain. The part I didn't quite understand is how it would interface with the other Gateway and how I could get 6 Gbps total internet throughput. Is there a reference I could look at to better understand?
– Doug
Jan 28, 2022 at 17:03
• VLAN was my primary understanding of load sharing with 2 separate gateways. Would appreciate further insight, if you would be kind enough to expand on this in your answer.
– Doug
Jan 28, 2022 at 17:03
• You don't mention the brand of devices, so I'm assuming Cisco. If you used HSRP for example, you would create two virtual gateway IPs: One IP is primary on the left gateway, the other is primary on the right. All your hosts on the left 3 switches use the left virtual IP; the ones on the right 3 use the right IP. If either gateway fails, the other one services all the hosts. Here is more info. Jan 28, 2022 at 18:18
• That's perfect. So that combines several concepts I was after which is : Aggregating 3 links together to make it higher bandwidth, Distributing internet from both gateways for 6Gbps total bandwidth, Distributing the internet to individual points and also automatically failing over. Thank you.
– Doug
Jan 28, 2022 at 18:37
• If you find the answer helpful, consider accepting it so the question doesn't keep popping up. Jan 28, 2022 at 19:19

I would like to implement a linear daisy chain for the purpose of transmitting internet over a considerable distance.

A much better design for covering distance is the use of optical fiber which can run for dozens of kilometers in a single link.

Chained switches increase latency, introduce multiple single points of failure and, depending in the chain length, disables spanning-tree protocols.

The motivation behind 3 cables is to triple the bandwidth.

Note that aggregated links (LAG) only increase the aggregated bandwidth of the logical link (in best case). No single flow can exceed the speed of a single physical link. Using a link with a higher link speed (e.g. 10G instead of 3x 1G), there's no need for fiddling with VLAN traffic distribution (which doesn't usually work with LAG).

• Thanks. I appreciate your answer. However, the hardware and distances are constraints. There is nothing that I can do to change those factors that I have discussed in the post.
– Doug
Jan 28, 2022 at 16:55