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The router at the top is from the ISP and I have no control over things like WAN, NAT, etc.
Network 192.168.1.1/24 is fine, but I cannot get inter-VLAN routing between VLANs 1 and 55.
PC 1 cannot even ping the gateway of the other network at 192.168.55.1.
PC 2 cannot even ping the gateway of the other network at 192.168.1.1.
What am I missing here?
You need to set up a static route on the ISP router for 192.168.55.0/24 (or 192.168.0.0/16 already) via 192.168.1.2. Without that route, any IP address not from 192.168.1.0/24 (attached locally) is routed to WAN.
The static route is also necessary for any host that is attached to 192.168.1.0/24 and using 192.168.1.1 as default gateway. They should rather use 192.168.1.2 as default gateway (requiring "hairpin routing" on the L3 switch, not sure if that's an issue).
On the L3 switch you need to use ip route 0.0.0.0 192.168.1.1. ip default-gateway is only functional when ip routing is not set and the switch is L2 only.
Of course, hosts on 192.168.55.0/24 need to use 192.168.55.1 as default gateway.
If you can't configure the ISP router at all, you need to either replace it or put a NAT router between it and your network.
@Zac67, you were spot on. Thanks so much! Adding the default route made a difference.
The only additional thing would have been that route entered in the ISP router in order for VLAN 55 to be reached, but the router I have just doesn't have that capability (Google Fiber). I think all the "No" instances in the diagram have to do with this fact, unless I am mistaken.
As an alternative, statically addressing an end host (see PC3) and using the VLAN 1 SVI IP address (192.168.1.102) as its default gateway allows for connectivity.
I have made a new diagram, with more of a complete picture, as there were actually additional goals past the initial inter-VLAN routing, like reaching the Internet from all the networks and so on.
NOTE: In the process of updating the documentation, some end host IP addresses changed but that should be negligible as the original diagram is now obsolete and the networks remain the same.
