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