Routers on the same fiber optic cable but with different IP addresses on different subnets

You can connect multiple routers on the same fiber optic cable using different subnets by configuring static routes or using firewalls/VLANs to manage traffic between them.Network ConfigurationWhen ro...

Routers on the same fiber optic cable but with different IP addresses on different subnets

You can connect multiple routers on the same fiber optic cable using different subnets by configuring static routes or using firewalls/VLANs to manage traffic between them.

Network Configuration

When routers share a single fiber connection but operate on different IP subnets, each router must have its own default gateway for its subnet. Devices connected to each router will use that router as their gateway, and communication between subnets requires routing rules or a Layer 3 device to forward traffic appropriately .

Options for Connecting Routers

  1. Direct Fiber to Firewalls or Routers
    • Connect the fiber to each router or firewall interface.
    • Assign each interface an IP in a new connectivity subnet.
    • Configure static routes on each router to reach the other subnet via the opposite router's IP on the connectivity segment .
    • This setup allows traffic separation and security filtering but may limit throughput compared to a switch.
  2. Using a Layer 3 Switch
    • Connect both routers to a Layer 3 switch.
    • Configure VLANs for each subnet and route traffic between VLANs.
    • This allows higher throughput and centralized routing while keeping subnets logically separated .
  3. Single WAN Port with Multiple IPs
    • Some ISPs allow multiple IPs on a single fiber port.
    • Assign each router a static IP from the ISP's different subnet blocks.
    • The ISP routes traffic to the correct IP, and NAT or firewall rules on each router handle internal traffic .
    • Ensure that each router's WAN interface uses the correct gateway for its subnet to avoid conflicts.

Important Considerations

  • Avoid overlapping subnets on the same physical network unless you implement VLANs or proper routing; otherwise, broadcast traffic can cause latency and connectivity issues .
  • Static routes must be configured on each router to allow devices on one subnet to reach devices on the other subnet. For example, Router A should have a route to Router B's subnet via Router B's IP on the shared segment .
  • Firewall rules may need adjustment to allow traffic between subnets while maintaining security.
  • Throughput limitations: Direct fiber connections without a switch may not achieve full LAN speeds if routing is handled by firewalls or routers .

Practical Example

  • Router A: 192.168.1.1/24
  • Router B: 192.168.2.1/24
  • Connectivity segment: 10.0.0.0/30
  • Router A static route: 192.168.2.0/24 via 10.0.0.2
  • Router B static route: 192.168.1.0/24 via 10.0.0.1 This allows devices on each subnet to communicate while keeping the networks logically separate.

Summary

Connecting routers on the same fiber with different subnets is feasible by using static routing, VLANs, or multiple IPs on a single WAN port. Proper configuration of gateways, routes, and firewall rules ensures that each subnet operates independently while allowing controlled inter-subnet communication. Avoid overlapping subnets on the same physical network to prevent broadcast conflicts and latency spikes .

Mar 04, 2026

Connect two routers with different subnet

You say these routers support port-based VLANs, so I''d do it like this: Set up a port-based VLAN (untagged) on both

Jul 01, 2026

Can I connect two routers to one fiber modem?

Learn how to connect two routers to one fiber modem for better WiFi coverage. Discover setup steps, potential issues, and network

Jan 29, 2026

Is it possible to connect two wifi routers to same fiber modem

But I would like to know, technically is it possible to connect new router directly to the fiber modem? (my fiber modem has extra RJ45

Aug 28, 2025

Same network but different IP address?

When set up correctly, you should find that all devices on your network automatically have an IP address that starts

Sep 21, 2025

Communication between different subnet MASKS with IP address that

This would break down if i chose in the same subnets different IP''s, they would not be able to ping each other with out

Jul 18, 2026

Configuring static routing for 2 routers with different subnets

Both of my routers are using Openwrt and I am not too sure about how to configure a LAN port on both routers to be

May 09, 2026

Routing the same subnet in two locations / gateways?

My problem is that I have machines on the same subnet in both locations, but I dont want to traverse the trunk if my traffic stays

Jun 29, 2026

Can an ISP provide two static IPs over a single cable?

A former ISP, sonic , offered six static IP addresses with their monthly service. You don''t need a router. You just need a hub or

Jul 30, 2025

How are IP addresses assigned for two routers in the same network?

In case my other router is connected to the LAN port of the main, will the second router be on the 192.168.0.2 e.g. ? or

Mar 06, 2026

Spectrum Fiber Multiple IPs

We have a 500m fiber connection and for years have only had one single IP. Recently I had a block of IPs added so

Apr 24, 2026

I tried different Switches and also reduced my network setup to 1 device + 2 Fritzboxes but I still always experience

Jun 29, 2026

What are the implications of having two subnets on the same switch?

Can anyone tell me what some of the implications of having two different subnets on the same switch would be if

Apr 16, 2026

Why Devices on Different VLANs but on the Same Subnet Can

A common confusion arises when devices are on different VLANs but share the same IP subnet: they can''t

Jan 11, 2026

Running two subnets over the same physical LAN

The first two are reasons to have a separate broadcast domain for IP camera''s but not necessarily reasons not to have two subnets

Sep 16, 2025

How To: One Internet connection – Two Private LANs

You can use any two private IP address ranges as long as they are different. The top router (“Internet”) takes the single Internet

Aug 11, 2025

Multiple hosts with same ip/subnet seperated by router possible?

You cannot have the same IP network on different layer 3 interfaces of the same gateway device (router or layer 3

Sep 15, 2025

connect two routers with different subnet

Do those routers have a third interface you can use to physically connect them (assuming they are in the same location

Sep 10, 2025

Two homes one internet, separating the networks

If you do, keep in mind that the router will need to do its job and "route" all the traffic between the different subnets. With a single

Jul 07, 2026

Router interface on same subnet

Could someone please explain why a router can''t have 2 interfaces on same subnet? Do routers use network

Jul 14, 2026

Direct Fiber between subnets

A fiber connection is really no different than just running an ethernet cable between the two buildings, at least not from

Nov 13, 2025

Why can''t devices in different subnets talk with each other?

Devices in different subnets can communicate. That is the purpose of a router. Routers route packets between

Mar 01, 2026

A single fiber connection into two independent routers

There is no need to get extra IP, it doesn''t really solve some potential issues. The easiest way to do is, terminate your ISP

Nov 28, 2025

2 LANs 2 subnets over fiber

You will then want to configure subinterfaces on your ethernet port on the router- each IP address on the ethernet

May 15, 2026

ISP providing two IPs blocks on two subnets : r/networking

ISP providing two IPs blocks on two subnets I''ve run into a situation where I''m in a bit over my head and was hoping someone could

Aug 03, 2025

Two routers on a fibre optic network? : r/HomeNetworking

The junction box (pictured) has a straight connection from the fibre modem to a single Ethernet connection in one of the room A in

Sep 02, 2025

One fibre line into two separate networks? : r/HomeNetworking

Two of the Ethernet ports (E1 and E2) are configured with static IP addresses on different small subnets with private IP spaces, like

Jul 01, 2026

Two subnets in the same ethernet cable?

Hi, we have both iptv and internet from our isp and the iptv is on different subnet on dedicated ports on the

May 22, 2026

Is it possible to configure a router with multiple IP subnets?

That is going to depend on the router. For example, a Ubiquiti USG has dual LAN ports, and

Broadcast Optical Network Insights

Need Reliable Broadcast Optical Network Equipment?

Contact us today for product inquiries, custom kits, or integration support