I am using my 2 arista’s (at different site) to terminate a P-T-P connection. Currently I have the port vlan tagged and then interface vlan XX and then everything of the int vlan. But I could actually make the port L3 and do it all there.
– SVI is a virtual L3 interface. It can have multiple underlying L2 interfaces. This mean you can have multiple users part of that VLAN and hence you can configure the SVI as a gateway for multiple hosts in a VLAN
– However, if you make a physical port L3 using “no switchport”, no other interface can be part of that subnet. By default, any traffic that will come on that interface will go to the default VLAN which VLAN1. L3 interface will not understand do1q packets. It is mostly used to route data-plane traffics.
As Aniket said, if you need to share at Layer2 then the trunking is needed.
I like to make Layer3-only links directly connected from router interface to router interface (no switchport) if you don’t need to share that link at Layer2. If it is really Layer3-only, then it seem simpler to me putting the Layer3 on the interface itself rather than bringing Layer2 in the story and using SVIs. I feel that when something happens (link flap, down/up/ L2-something), then I would rather have the states and convergence done ASAP, not relying on Layer2-then-Layer3 to run. Layer3 only.
