SIOCGSRCIPADDR obtains the associated source address (by Source Address Selection algorithm, which is part of RFC 3484 (Default Address Selection)) for each of the IPv6 addresses passed in an array. The label and precedence of each source and destination address are also returned. This information is ultimately used to sort the IPv6 and IPv4 destination addresses, using the algorithm described in the RFC 3484 (Default Address Selection) for destination addresses.

Argument: An array of IPv6 and IPv4 destination addresses, with a total count of the addresses being passed. The IPv4 destination addresses must be passed in as IPv4-mapped IPv6 addresses. The only SisPreferences currently recognized by the z/OS® Communications Server IP stack are SisSrcPreferPublic and SisSrcPreferTmp. Upon return from the IOCTL invocation, the array structure is to include a source IP address for each of the array elements associated with the destination address that is being passed. This source address is determined by the stack, using the Source Address Selection algorithm defined in RFC 3484 (Default Address Selection). If a source address cannot be determined for a specific destination IP address (for example, if there is no route to the destination), a null value is placed in the array element's IP source address field (SisSrcIPaddr).

DCL 1 SrcIpSelect Based Bdy(Word),
        2 SisHeader,
          3 SisVersion Fixed(8),     /* Version of the IOCTL interface
                                        This should be SrcIpSelect_V2*/
          3 SisPreferences Bit(8),   /* IPv6_ADDR_PREFERENCES_FLAGS
                                        byte-4 (see BPXYSOCK)        */
            /* The following mapping of SisPreferences must          */
            /* match the mapping of IPv6_ADDR_PREFERENCES_FLAGS      */
            /* in BPXYSOCK (see BPXYSOCK)                            */
            5 *                  Bit(2), /* Invalid flags            */
            5 SisSrcPreferNoncga Bit(1), /* IPV6_PREFER_SRC_NONCGA
                                            Prefer non-crypto        */
            5 SisSrcPreferCga    Bit(1), /* IPV6_PREFER_SRC_CGA
                                            Prefer cryptographic     */
            5 SisSrcPreferPublic Bit(1), /* IPV6_PREFER_SRC_PUBLIC
                                            Prefer public addr       */
            5 SisSrcPreferTmp    Bit(1), /* IPV6_PREFER_SRC_TMP
                                            Prefer temp address      */
            5 SisSrcPreferCoa    Bit(1), /* IPV6_PREFER_SRC_COA
                                            Prefer care-of addr      */
            5 SisSrcPreferHome   Bit(1), /* IPV6_PREFER_SRC_HOME
                                            Prefer home address      */
          3 SisSrcAddrFlagsIn Bit(8),  /* Source IP address flags
                                       (input to IOCTL)              */
            5 SisIgnoreSourceVIPA Bit(1), /*  B'1' indicates that
                                       source VIPA should be ignored */
            5 *             Bit(7),  /*                              */
          3 *               Char(1), /* Available                    */
          3 SisNumEntries   Fixed(32), /* Number of destination
                                       addresses for which a source
                                       address must be selected      */
        2  SisIpAddrs(*),
          3 SisDestInfo,              /* Destination IPaddr data     */
           4 SisDestIPaddr  Char(16), /* Destination IP address. Can
                                        contain a native IPv6 address,
                                        or a mapped IPv4 address     */                                        
            5 SisIpV4prefix   Char(12),  /* IP address prefix        */
              7 SisIpV4nulls    Char(10), /* Always nulls for IPv6
                                             mapped addresses        */
              7 SisIpV4mapped   Char(2), /* IPv6 mapped prefix       */
            5 SisV4DestIPaddr Char(4), /* IPv4 address               */
           4 SisDestLabel      Fixed(16), /* Dest IP addr label      */
           4 SisDestPrecedence Fixed(16), /* Destaddr precedence     */
           4 *                 Char(4),                       
          3 SisSrcInfo,               /* Source IP address data      */
           4 SisSrcIPaddr   Char(16), /* Associated Source IP address
                                       (output from IOCTL)           */
           4 SisSrcLabel      Fixed(16), /* Src IP address label     */
           4 SisSrcPrecedence Fixed(16), /* Src Ipadr precedence     */
           4 SisSrcScopeID    Fixed(32),                      
          3 SisReturnInfo,             /* Other IOCTL output         */
           4 SisRetcode     Fixed(32), /* Return code from attempt to
                                       obtain a source address       */
           4 SisSrcAddrFlags Bit(8),  /* Source IP address flags
                                       (output from IOCTL            */
            5 SisSrcDeprecated Bit(1), /*  B'1' indicates address is
                                       deprecated (only applicable for
                                       native IPv6 addresses         */
            5 *             Bit(7),
           4 *              Char(3); /* Available                    */
DCL SrcIpSelect_V2      Fixed(8) Constant(2);
DCL SrcIpSelect_Version Fixed(8) Constant(2);