RADIUS attribute from rfc6572

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PMIP6-Home-IPv4-Gateway

specifies extensions to Proxy Mobile IPv6 protocol that
   enable IPv4 home address mobility support to the MN.  The PMIP6-Home-
   IPv4-Gateway attribute (Type value 161) is of type Address and
   contains the default gateway IPv4 address for the MN.  This address
   is populated into the PMIPv6 IPv4 Default-Router Address Option
   .  The address MUST belong to the subnet defined in the
   PMIP6-Home-IPv4-HoA attribute.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Type     |   Length      |   Home IPv4 default gateway
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
               address             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:
      PMIP6-Home-IPv4-Gateway 161.

   Length:
      = 6 octets

   Home IPv4 default gateway address:
      This field is of type Address and contains a 4-octet IPv4 default
      gateway address.

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