Which mode does a Citrix Administrator need to configure to allow a Citrix ADC to control the packetforwarding function based on the route table lookups?

Layer 3 mode configures the Citrix ADC to function as an IP router. In this mode, when the ADC receives a packet not destined for one of its own IP addresses, it performs a lookup in its internal routing table to determine the best path and the next-hop router. It then forwards the packet accordingly. This directly enables the ADC to control packet forwarding based on route table lookups, which is the core requirement of the question.

A. MBF: MAC-Based Forwarding (MBF) is a performance optimization within Layer 3 mode that forwards packets based on the destination MAC address of the next-hop router, bypassing some Layer 3 processing. It is not the fundamental mode for route-based forwarding.
B. USIP: Use Source IP (USIP) mode controls how the ADC presents the source IP address to back-end servers. It is a traffic-handling feature, not a packet-forwarding mode for the appliance itself.
C. Layer 2: In Layer 2 mode, the Citrix ADC acts as a bridge or switch, forwarding packets based on the destination MAC address. It does not use an IP routing table for forwarding decisions.

1. Citrix Product Documentation - Modes of Operation: "In Layer 3 mode

the Citrix ADC appliance forwards the packets that it receives

and are not destined to it

to the appropriate next-hop router as determined by its routing table."

Source: Citrix ADC 13.1 Product Documentation

Section: Networking > Modes of operation.

2. Citrix Product Documentation - IP Routing: "When the Citrix ADC appliance is in Layer 3 mode

it can route IP packets between networks... The appliance maintains an IP routing table with entries for all the subnets that it is connected to."

Source: Citrix ADC 13.1 Product Documentation

Section: Networking > IP Routing.

3. Citrix Product Documentation - Layer 2 Mode vs. Layer 3 Mode: "In Layer 2 mode

the appliance is a 'bump in the wire' and forwards packets based on data link layer (MAC) addresses... In Layer 3 mode

the appliance acts as a router and forwards packets based on network layer (IP) addresses."

Source: Citrix ADC 13.0 Product Documentation

Section: Networking > Networking Features and How-tos > Configuring Layer 2 and Layer 3 Modes.