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Fiber connection between two buildings

Occasional Collector

Fiber connection between two buildings


I'm a noob Network admin for a small business, and am gathering info on connecting two separate adjacent building networks via fiber.

Both networks have sonicwall firewalls, HP procurve switches with multiple vlans configured on each network and they have individual T1 connections. I'm looking to connect the two networks via Fiber. Can someone give me a little direction on how to do this... what's involved? best practices?


I already have someone to run the fiber. I have a general idea of how this is done, but am looking to verify I'm on the right track here.


I want to have connectivity between all vlans on all switches. I'm thinking I pick the main lan switches and just tag all the vlans on the connecting fiber ports and uplink ports.


So for example on network 1:

Switches are on default vlan 1

I have vlans 10, 20 and 30 tagged on ports 47 and 48 on Switches 1, 2, and 3 for uplinks to the other switches.


on network 2:

Switches on default vlan 1

I have vlans 40, 50, and 60 tagged on ports 47 and 48 on Switches 4, 5, and 6.


I'm planning to add Fiber modules to Switch 1 and 4 and tag all vlans 10 thru 60 on these modules. I'll also add tags for the vlans 10 thru 60 on ports 47 and 48 of the all the switches.


Any thing I'm missing with this plan? advice?





Honored Contributor

Re: Fiber connection between two buildings

It seems unlikely that you would want to trunk the VLANs between buildings - I am thinking that both buildings will have entirely separate IP subnets, OR, the subnets clash. Either way, the link would probably go through the local router/firewall.


Plus each site will presumably continue to use its local firewall to reach the internet, so trunking VLANs between buildings probably won't help much - linking the buildings probably just means that you will have a new path to route traffic for non-local campus subnets only. If you don't have clashing subnets and no security issues, you could link them switch-to-switch via a new point-to-point subnet, but that would depend on where your routing is being done.

Occasional Collector

Re: Fiber connection between two buildings

Our firewall/routers don't have fiber ports, so we won't be connecting there.


We do have seperated subnets/vlans for each building with exception of one, the Default Lan subnet is configured the same on each of the routers. The only devices that get ip addresses from this subnet are the switches. Would it be better to set these up as seperate subnets/vlans to avoid conflicts and then create yet another subnet/vlan specifically for the fiber ports that gets dhcp and routing directly from the switches?


The main reason we are doing this is not for internet, it's to have Internal systems(lighting, security, AV, etc...) all tied into a crestron system, and access both buildings from anywhere on the campus accross the fiber line, instead of out the firewall and accross the internet and back in the other firewall.

Honored Contributor

Re: Fiber connection between two buildings

Personally, for a campus network, I would like to have a management VLAN with all my management addresses on it, but having a separate management subnet for each building could also be an option.


You will need to decide whether you want the link between sites to be layer2 or routed.