ipoa

IPv4 options Address.

               +------+-----+-------------+
               | type | len | real saddr  |
               +------+----++-------------+
                           ^
                           |
                           |
                           |
+-------+-----------+------+---------+-------------+----------+
|l2 hdr |  ipv4 hdr |  ipv4 options  | tcp/udp hdr |   data   |
+-------+-----------+----------------+-------------+----------+

what is ipoa?

use IPv4 options to carray the real source address of the NAT-packet. The tcp and udp application can get real client IP address with ipoa.

which OS we support?

[root@localhost]cat /etc/redhat-release

CentOS Linux release 7.2.1511