Hi @grapevine,
Good to see you around again!
Agree as Mark said. It won't directly influence any L3 routing but it potentially (depending on the topology) could alter the L2 switching data path which could indirectly affect whether routing can take place. For example, if there was misconfiguration on SWB or an element of your design that severed connectivity between SWB and the firewall, or impacted the endpoints ability to reach the firewall's default gateway IP address then this could have an impact on the ability for routing to occur; if endpoints are using and SWB cannot forward to the firewall, routing cannot happen. It could cause an issue depending on the topology, design and configuration, but speaking from a technical theory perspective, routing would not be impacted as the introduction of an L2 switch only affects the L2/switching forwarding path. Don't take too much caution to what I'm saying, I'm probably making it seem like adding this switch is a bigger deal than it is. In all likelihood there shouldn't be any impact, I'm just reiterating as it's worth noting and considering your topology
It could be worth displaying a proposed basic diagram if there was any help you needed with that. There are considerations in designs with switches that they can be stacked if location permits, which would merge the control plane and have both SWA and SWB as the root since they are one logical device. This may be helpful and would simplify the integration/implementation and would also help with day-to-day management for you. If not stacked, also the consideration of including a link between SWA and SWB for redundancy and availability purposes. It does depend on the design and scale of the network, e.g. whether or not these switches (SWA and SWB) are distributions or access switches and where they sit within the topology, etc.
Hopefully that helps, but always happy to help with any other questions.
