Use client source IP address for back end communication in a v4-v6 load balancing configuration

Last published : Sep 24, 2026
In a v4-to-v6 load balancing configuration, for services with USIP disabled, the NetScaler appliance communicates to the related servers from one of the configured IPv6 SNIP (SNIP6) addresses.
For services with USIP enabled, you must set the global USIP NAT prefix parameter for making the related servers aware of the client’s IP address of the request packets. USIP NAT prefix is a global IPv6 prefix of length 32/40/48/56/64/96 bits configured on the NetScaler appliance.
For a load balancing service that has USIP enabled, the appliance translates the IPv4 request packet to an IPv6 packet and sets the source IP address of the translated IPv6 packet to a concatenation of:
  • the USIP NAT prefix of length of 32/40/48/56/64/96 bits.
  • zeros padded if the USIP NAT prefix length is less than 96 bits. Number of bits padded with zeros = 96-USIP NAT prefix length. For example, if the USIP NAT prefix length is 64, then the number of bits padded with zeros = 96-64 = 32.
  • the IPv4 source address that was received in the request packet. In other words, the last 32 bits of the source IPv6 address is set to the IPv4 address of the client.
On receiving an IPv6 response packet from the server, the NetScaler appliance translates the IPv6 packet to an IPv4 packet and sets the destination IP address of the translated IPv4 packet to the last 32 bits of the destination IP address of the IPv6 packet.
Note: This feature is not supported for NetScaler Gateway configuration and, content switching and cache redirection load balancing configurations.
Related information

Configuration Steps

Configuring USIP for a v4-to-v6 load balancing configuration consists of the following tasks:
To add a global USIP NAT prefix by using the CLI:
  • set ipv6 -usipnatprefix <prefix/prefix_length>
  • show ipv6
To add a global USIP NAT prefix by using the GUI:
  1. Navigate to System > Network, and click Change IPv6 Settings.
  2. On the Configure Configuration for IPV6 screen, set the USIP NAT Prefix parameter.

Sample configuration

> set ipv6 -usipnatprefix 2001:DB8:90::/64
Done

> enable ns mode USIP
Done

> add lb vserver LBVS-1 HTTP 203.0.113.90 80
Done

> add service SVC-1 2001:DB8:5001::30 HTTP 80 -usip yes
Done

> add service SVC-2 2001:DB8:5001::60 HTTP 80 -usip yes
Done

> bind lb vserver LBVS-1 SVC-1
Done

> bind lb vserver LBVS-1 SVC-2
Done