KUSANAGIをVPN経由で運用監視したい(インターネット上に平文で監視プロトコルを流したりしたくない場合など)、SoftEtherVPNがラクで良いです。
ここではマネジメントネットワークとして、SoftEtherVPNの仮想NICをCentOS7(KUSANAGI 7.8.2)に追加する方法をまとめます。 

1.SoftEtherVPNのアカウントを用意します。

仮想HUB名:MANAGE
ユーザ名:host2
パスワード:********
IPアドレス:172.16.255.2/24
ゲートウェイ:なし
仮想NIC名:vpn_mgmt0

2.SoftEtherVPN Clientをダウンロードしコンパイルします。

# make
--------------------------------------------------------------------

SoftEther VPN Client (Ver 4.21, Build 9613, Intel x64 / AMD64) for Linux Install Utility
Copyright (c) SoftEther Project at University of Tsukuba, Japan. All Rights Reserved.

--------------------------------------------------------------------
(中略)
make[1]: Entering directory `/root/tmp/vpnclient'
Preparing SoftEther VPN Client...
ranlib lib/libcharset.a
ranlib lib/libcrypto.a
ranlib lib/libedit.a
ranlib lib/libiconv.a
ranlib lib/libintelaes.a
ranlib lib/libncurses.a
ranlib lib/libssl.a
ranlib lib/libz.a
ranlib code/vpnclient.a
gcc code/vpnclient.a -O2 -fsigned-char -pthread -m64 -lm -ldl -lrt -lpthread -L./ lib/libssl.a lib/libcrypto.a lib/libiconv.a lib/libcharset.a lib/libedit.a lib/libncurses.a lib/libz.a lib/libintelaes.a -o vpnclient
ranlib code/vpncmd.a
gcc code/vpncmd.a -O2 -fsigned-char -pthread -m64 -lm -ldl -lrt -lpthread -L./ lib/libssl.a lib/libcrypto.a lib/libiconv.a lib/libcharset.a lib/libedit.a lib/libncurses.a lib/libz.a lib/libintelaes.a -o vpncmd

--------------------------------------------------------------------
The preparation of SoftEther VPN Client is completed !


# ./vpnclient start
The SoftEther VPN Client service has been started.

3.CLI版ユーティリティで接続先設定を保存します

# ./vpncmd
vpncmd command - SoftEther VPN Command Line Management Utility
SoftEther VPN Command Line Management Utility (vpncmd command)
Version 4.21 Build 9613 (English)
Compiled 2016/04/24 16:39:47 by yagi at pc30
Copyright (c) SoftEther VPN Project. All Rights Reserved.

By using vpncmd program, the following can be achieved. 

(中略)
Connected to VPN Client "localhost".

VPN Client>NicCreate mgmt0
NicCreate command - Create New Virtual Network Adapter
The command completed successfully.

VPN Client>NicEnable mgmt0
NicEnable command - Enable Virtual Network Adapter
The command completed successfully.

VPN Client>AccountCreate MANAGE /SERVER:sesrv.nkjg.info:443 /HUB:MANAGE /USERNAME:host2 /NICNAME:mgmt0
AccountCreate command - Create New VPN Connection Setting
The host name and port number specification is invalid. 
Please specify using the format of host name:port number, or IP address:port number.
Destination VPN Server Host Name and Port Number: 443
The command completed successfully.

The specified VPN Connection Setting does not exist.
VPN Client>AccountPasswordSet MANAGE 
AccountPasswordSet command - Set User Authentication Type of VPN Connection Setting to Password Authentication
Please enter the password. To cancel press the Ctrl+D key.
Password: **********
Confirm input: **********
Specify standard or radius: standard
The command completed successfully.

VPN Client>AccountConnect MANAGE 
AccountConnect command - Start Connection to VPN Server using VPN Connection Setting
The command completed successfully.

VPN Client>exit 

4.自動起動設定を施します

# cat /etc/sysconfig/network-scripts/ifcfg-vpn_mgmt0 
TYPE="Ethernet"
BOOTPROTO="static"
IPADDR=172.16.255.2
NETMASK=255.255.255.0
NAME="vpn_mgmt0"

DEVICE="vpn_mgmt0"
ONBOOT="no"
NM_CONTROLLED="no"

# cat /etc/rc.local
/usr/local/vpnclient/vpnclient start
sleep 2
/usr/local/vpnclient/vpncmd /client localhost /cmd AccountConnect MANAGE
sleep 30
/sbin/ifup vpn_mgmt0

# chmod +x /etc/rc.local 

 以上で、ホスト再起動後も該当ホストに対してICMPが復帰するなどすれば、問題なく疎通しています。

参考サイト

http://rauq04.blogspot.jp/2014/02/linux-softether-vpn-client-vpngate.html
https://ja.softether.org/4-docs/1-manual/6/6.2
http://tsuchinoko.dmmlabs.com/?p=1371