Which data flow direction is protected in a zero trust firewall deployment that is not protected in a perimeter-only firewall deployment?

Outbound traffic is protected by both perimeter and Zero Trust firewalls, as it crosses the network boundary.

North-south traffic is the primary focus of protection for traditional perimeter firewalls, so it's already protected in that model.

Inbound traffic is protected by both perimeter and Zero Trust firewalls, as it crosses the network boundary from external sources.

A Zero Trust model assumes compromise is possible internally and applies security policies to "east-west" traffic, which flows laterally between devices and applications *within* the internal network, thus providing protection against lateral movement, a capability not inherently present in perimeter-only deployments.