Which tool enables a network designer to route traffic based on the source IP address?

Source routing refers to the IP header option where the originating host specifies the forwarding path inside the packet itself - it is a host-level mechanism, not a network design routing tool.

MPLS Layer 3 VPNs use VRF tables and label switching to separate customer routing domains - they forward based on VPN labels and destination prefixes, not source IP addresses.

Policy-based routing uses route maps with match statements (e.g., match ip address to identify source IP via an ACL) and set statements (e.g., set ip next-hop) to override the normal destination-based routing table lookup. It is applied inbound on an interface and can selectively forward traffic from specific source addresses out a different path than normal routing would choose.

Unicast Reverse Path Forwarding is a security feature that drops packets whose source IP does not match the expected ingress interface according to the routing table - it is not used to route or forward traffic based on source IP.