A Citrix Administrator needs to use a client’s IP address as the source IP address for Citrix ADC-to- server connections. Which Citrix ADC mode can the administrator use to meet this requirement?

The Use Source IP (USIP) mode configures the Citrix ADC to use the client's original IP address as the source IP address for connections to the backend servers. When USIP is enabled, the server sees the connection as originating directly from the client, which is essential for scenarios requiring client IP logging, specific access controls, or applications that depend on the original source IP. For this mode to function correctly, the backend servers must use the Citrix ADC's Subnet IP (SNIP) as their default gateway to ensure the return traffic is routed back through the ADC.

A. USNIP: Use Subnet IP (USNIP) mode uses a Subnet IP address owned by the ADC as the source IP, hiding the client's original IP from the server.
B. Layer 2: This is a network forwarding mode where the ADC operates as a "bump-in-the-wire." It does not inherently define the source IP address policy for server-side connections.
C. Layer 3: This is the default routing mode for the ADC. In this mode, the ADC typically uses a SNIP address for server connections unless USIP is explicitly enabled.

1. Citrix ADC 13.1 Product Documentation. Configuring Source IP Address for Server Connections. "Use Source IP (USIP) mode. In USIP mode, the Citrix ADC appliance uses the client’s IP address (the source IP address) as the source IP address in the packet that it sends to the server."

2. Citrix ADC 13.1 Product Documentation. Networking > Network Topology > Modes of Operation. This document describes Layer 2 and Layer 3 modes as network topologies, distinct from the source IP address modes like USIP and USNIP. It states, "In Layer 3 mode, the appliance forwards packets between the client and server subnets." This forwarding typically uses a SNIP by default.

3. Citrix ADC 13.1 Product Documentation. Networking > IP Addressing > Subnet IP Addresses (SNIPs). "A SNIP is used in connection management and server monitoring. The Citrix ADC appliance uses a SNIP address as a source IP address to connect to the servers..." This confirms the function of USNIP mode.