Device on L2 interface trying to reach L3 interface on same subnet

[Claw4609]

Are you able to have a device connected on a layer 2 interface be able to reach a layer 3 gateway on the same subnet? We are able to get this working with a vlan interface when its on a different subnet.

Scenario:

Sub interface ethernet1/1.100 with IP address 10.10.100.1/24 and tag 100

Ethernet 1/2: Layer 2 interface

Device with IP address 10.10.100.100 connected to ethernet 1/2

We want device 10.10.100.100 to be able to reach its gateway at 10.10.100.1. 

[seb_rupik]

Hi there,

The topology you are describing isn't one I have ever seen implemented and begs the question why not use a VLAN interface and use the sub-interfaces as a trunk link?

Looking at your config, I notice that the two interfaces in question do not belong to any VLAN. I suggest you create one and attach it to both Eth1/1.100 and Eth1/2 and repeat your testing.

cheers,

Seb.

[Claw4609]

Eth1/1.100 is a layer 3 interface and it doesnt look like I can attached a vlan to that. I have created vlan 100 and attached it to just eth1/2 to see if that would work but it didnt. 

The reasoning for the setup is we are looking to have a dedicated mgmt interface of the device have a separate port on the firewall. So in our case eth1/1 is the LAN interface which we have multiple sub interfaces on for our L3 gateways. One of those gateways is a management subnet. We would theoretically like an access port on the firewall for a device on the same subnet as the management subnet 

[seb_rupik · Accepted solution]

Hi there,

The only way you will get this to work is to convert Eth1/1 to a Layer2 interface with sub-interfaces and create a VLAN interface for each of the VLANs carried on Eth1/1 and that you want the firewall to be gateway for.

cheers,

Seb.

[Claw4609]

Sounds good, thanks for the help.