投稿者: user

何をするか

外出先のインターネットからクライアントVPNを使って自宅NWに接続する。

OpenVPNサーバの構築

yum install -y qemu-img

必要なパッケージをインストール

yum –enablerepo=epel install openvpn easy-rsa

作業ディレクトリを作成してコピーして移動。

mkdir /etc/openvpn/easy-rsa
cp /usr/share/easy-rsa/3.0.7/* /etc/openvpn/easy-rsa/ -R
cd /etc/openvpn/easy-rsa

CA(認証局)の初期化。

./easyrsa init-pki

CA(認証局)を作成。

./easyrsa build-ca

CA秘密鍵のパスワードが聞かれるので任意のパスワードを入力。

Enter New CA Key Passphrase: 
Re-Enter New CA Key Passphrase: 

処理が完了すると以下のファイルが作成される。

CA証明書：ca.crt
CA秘密鍵：ca.key

DH(Diffie-Hellman)パラメータの生成。

./easyrsa gen-dh
・DHパラメータ
/etc/openvpn/easy-rsa/pki/dh.pem

サーバ用秘密鍵、証明書の作成
※nonpassオプションをつけるとパスフレーズを省略できる。

./easyrsa build-server-full server_1

クライアント用証明書、秘密鍵の作成
※nonpassオプションをつけるとパスフレーズを省略できる。

./easyrsa build-client-full client_1

CA秘密鍵のパスワードが聞かれるのでパスワードを入力

Enter pass phrase for /etc/openvpn/easy-rsa/pki/private/ca.key:

処理が完了すると以下のファイルが作成される。
サーバ用証明書：client_1.crt
サーバ用秘密鍵：client_1.key

OpenVPNのテンプレコンフィグをコピー。

cp /usr/share/doc/openvpn*/sample/sample-config-files/server.conf server_1.conf

メインの設定ファイルを編集。

vi /etc/openvpn/server_1.conf
####
#################################################
# Sample OpenVPN 2.0 config file for            #
# multi-client server.                          #
#                                               #
# This file is for the server side              #
# of a many-clients <-> one-server              #
# OpenVPN configuration.                        #
#                                               #
# OpenVPN also supports                         #
# single-machine <-> single-machine             #
# configurations (See the Examples page         #
# on the web site for more info).               #
#                                               #
# This config should work on Windows            #
# or Linux/BSD systems.  Remember on            #
# Windows to quote pathnames and use            #
# double backslashes, e.g.:                     #
# "C:\\Program Files\\OpenVPN\\config\\foo.key" #
#                                               #
# Comments are preceded with '#' or ';'         #
#################################################

# Which local IP address should OpenVPN
# listen on? (optional)
;local a.b.c.d

# Which TCP/UDP port should OpenVPN listen on?
# If you want to run multiple OpenVPN instances
# on the same machine, use a different port
# number for each one.  You will need to
# open up this port on your firewall.
port 1194

# TCP or UDP server?
;proto tcp
proto udp4

# "dev tun" will create a routed IP tunnel,
# "dev tap" will create an ethernet tunnel.
# Use "dev tap0" if you are ethernet bridging
# and have precreated a tap0 virtual interface
# and bridged it with your ethernet interface.
# If you want to control access policies
# over the VPN, you must create firewall
# rules for the the TUN/TAP interface.
# On non-Windows systems, you can give
# an explicit unit number, such as tun0.
# On Windows, use "dev-node" for this.
# On most systems, the VPN will not function
# unless you partially or fully disable
# the firewall for the TUN/TAP interface.
;dev tap
dev tun

# Windows needs the TAP-Win32 adapter name
# from the Network Connections panel if you
# have more than one.  On XP SP2 or higher,
# you may need to selectively disable the
# Windows firewall for the TAP adapter.
# Non-Windows systems usually don't need this.
;dev-node MyTap

# SSL/TLS root certificate (ca), certificate
# (cert), and private key (key).  Each client
# and the server must have their own cert and
# key file.  The server and all clients will
# use the same ca file.
#
# See the "easy-rsa" directory for a series
# of scripts for generating RSA certificates
# and private keys.  Remember to use
# a unique Common Name for the server
# and each of the client certificates.
#
# Any X509 key management system can be used.
# OpenVPN can also use a PKCS #12 formatted key file
# (see "pkcs12" directive in man page).
#ca ca.crt
ca /etc/openvpn/easy-rsa/pki/ca.crt

#cert server.crt
cert /etc/openvpn/easy-rsa/pki/issued/server_r.crt

#key server.key  # This file should be kept secret
key /etc/openvpn/easy-rsa/pki/private/server_r.key

# Diffie hellman parameters.
# Generate your own with:
#   openssl dhparam -out dh2048.pem 2048
#dh dh2048.pem
dh /etc/openvpn/easy-rsa/pki/dh.pem

# Network topology
# Should be subnet (addressing via IP)
# unless Windows clients v2.0.9 and lower have to
# be supported (then net30, i.e. a /30 per client)
# Defaults to net30 (not recommended)
;topology subnet

# Configure server mode and supply a VPN subnet
# for OpenVPN to draw client addresses from.
# The server will take 10.8.0.1 for itself,
# the rest will be made available to clients.
# Each client will be able to reach the server
# on 10.8.0.1. Comment this line out if you are
# ethernet bridging. See the man page for more info.
server 10.8.0.0 255.255.255.0

# Maintain a record of client <-> virtual IP address
# associations in this file.  If OpenVPN goes down or
# is restarted, reconnecting clients can be assigned
# the same virtual IP address from the pool that was
# previously assigned.
ifconfig-pool-persist ipp.txt

# Configure server mode for ethernet bridging.
# You must first use your OS's bridging capability
# to bridge the TAP interface with the ethernet
# NIC interface.  Then you must manually set the
# IP/netmask on the bridge interface, here we
# assume 10.8.0.4/255.255.255.0.  Finally we
# must set aside an IP range in this subnet
# (start=10.8.0.50 end=10.8.0.100) to allocate
# to connecting clients.  Leave this line commented
# out unless you are ethernet bridging.
;server-bridge 10.8.0.4 255.255.255.0 10.8.0.50 10.8.0.100

# Configure server mode for ethernet bridging
# using a DHCP-proxy, where clients talk
# to the OpenVPN server-side DHCP server
# to receive their IP address allocation
# and DNS server addresses.  You must first use
# your OS's bridging capability to bridge the TAP
# interface with the ethernet NIC interface.
# Note: this mode only works on clients (such as
# Windows), where the client-side TAP adapter is
# bound to a DHCP client.
;server-bridge

# Push routes to the client to allow it
# to reach other private subnets behind
# the server.  Remember that these
# private subnets will also need
# to know to route the OpenVPN client
# address pool (10.8.0.0/255.255.255.0)
# back to the OpenVPN server.
#;push "route 192.168.10.0 255.255.255.0"
#;push "route 192.168.20.0 255.255.255.0"
push "route 192.168.0.0 255.255.255.0"

# To assign specific IP addresses to specific
# clients or if a connecting client has a private
# subnet behind it that should also have VPN access,
# use the subdirectory "ccd" for client-specific
# configuration files (see man page for more info).

# EXAMPLE: Suppose the client
# having the certificate common name "Thelonious"
# also has a small subnet behind his connecting
# machine, such as 192.168.40.128/255.255.255.248.
# First, uncomment out these lines:
;client-config-dir ccd
;route 192.168.40.128 255.255.255.248
# Then create a file ccd/Thelonious with this line:
#   iroute 192.168.40.128 255.255.255.248
# This will allow Thelonious' private subnet to
# access the VPN.  This example will only work
# if you are routing, not bridging, i.e. you are
# using "dev tun" and "server" directives.


# EXAMPLE: Suppose you want to give
# Thelonious a fixed VPN IP address of 10.9.0.1.
# First uncomment out these lines:
;client-config-dir ccd
;route 10.9.0.0 255.255.255.252
# Then add this line to ccd/Thelonious:
#   ifconfig-push 10.9.0.1 10.9.0.2

# Suppose that you want to enable different
# firewall access policies for different groups
# of clients.  There are two methods:
# (1) Run multiple OpenVPN daemons, one for each
#     group, and firewall the TUN/TAP interface
#     for each group/daemon appropriately.
# (2) (Advanced) Create a script to dynamically
#     modify the firewall in response to access
#     from different clients.  See man
#     page for more info on learn-address script.
;learn-address ./script

# If enabled, this directive will configure
# all clients to redirect their default
# network gateway through the VPN, causing
# all IP traffic such as web browsing and
# and DNS lookups to go through the VPN
# (The OpenVPN server machine may need to NAT
# or bridge the TUN/TAP interface to the internet
# in order for this to work properly).
;push "redirect-gateway def1 bypass-dhcp"

# Certain Windows-specific network settings
# can be pushed to clients, such as DNS
# or WINS server addresses.  CAVEAT:
# http://openvpn.net/faq.html#dhcpcaveats
# The addresses below refer to the public
# DNS servers provided by opendns.com.
;push "dhcp-option DNS 208.67.222.222"
;push "dhcp-option DNS 208.67.220.220"

# Uncomment this directive to allow different
# clients to be able to "see" each other.
# By default, clients will only see the server.
# To force clients to only see the server, you
# will also need to appropriately firewall the
# server's TUN/TAP interface.
#;client-to-client
client-to-client

# Uncomment this directive if multiple clients
# might connect with the same certificate/key
# files or common names.  This is recommended
# only for testing purposes.  For production use,
# each client should have its own certificate/key
# pair.
#
# IF YOU HAVE NOT GENERATED INDIVIDUAL
# CERTIFICATE/KEY PAIRS FOR EACH CLIENT,
# EACH HAVING ITS OWN UNIQUE "COMMON NAME",
# UNCOMMENT THIS LINE OUT.
;duplicate-cn

# The keepalive directive causes ping-like
# messages to be sent back and forth over
# the link so that each side knows when
# the other side has gone down.
# Ping every 10 seconds, assume that remote
# peer is down if no ping received during
# a 120 second time period.
keepalive 10 120

# For extra security beyond that provided
# by SSL/TLS, create an "HMAC firewall"
# to help block DoS attacks and UDP port flooding.
#
# Generate with:
#   openvpn --genkey --secret ta.key
#
# The server and each client must have
# a copy of this key.
# The second parameter should be '0'
# on the server and '1' on the clients.
tls-auth ta.key 0 # This file is secret

# Select a cryptographic cipher.
# This config item must be copied to
# the client config file as well.
# Note that v2.4 client/server will automatically
# negotiate AES-256-GCM in TLS mode.
# See also the ncp-cipher option in the manpage
cipher aes-256-cbc
#auth sha256

# Enable compression on the VPN link and push the
# option to the client (v2.4+ only, for earlier
# versions see below)
;compress lz4-v2
;push "compress lz4-v2"

# For compression compatible with older clients use comp-lzo
# If you enable it here, you must also
# enable it in the client config file.
#;comp-lzo
comp-lzo

# The maximum number of concurrently connected
# clients we want to allow.
;max-clients 100
max-clients 100

# It's a good idea to reduce the OpenVPN
# daemon's privileges after initialization.
#
# You can uncomment this out on
# non-Windows systems.
#;user nobody
#user nobody
#;group nobody
#group nobody

# The persist options will try to avoid
# accessing certain resources on restart
# that may no longer be accessible because
# of the privilege downgrade.
persist-key
persist-tun

# Output a short status file showing
# current connections, truncated
# and rewritten every minute.
#status openvpn-status.log
status /var/log/openvpn-status.log

# By default, log messages will go to the syslog (or
# on Windows, if running as a service, they will go to
# the "\Program Files\OpenVPN\log" directory).
# Use log or log-append to override this default.
# "log" will truncate the log file on OpenVPN startup,
# while "log-append" will append to it.  Use one
# or the other (but not both).
#;log         openvpn.log
log-append         /var/log/openvpn.log
log   /var/log/openvpn.log

# Set the appropriate level of log
# file verbosity.
#
# 0 is silent, except for fatal errors
# 4 is reasonable for general usage
# 5 and 6 can help to debug connection problems
# 9 is extremely verbose
verb 3

# Silence repeating messages.  At most 20
# sequential messages of the same message
# category will be output to the log.
;mute 20

# Notify the client that when the server restarts so it
# can automatically reconnect.
explicit-exit-notify 1
####

vpnux Clientの設定

vpnux Clientを起動して「プロファイル」→「追加」を押下する。
■一般設定
プロファイル名：任意
VPNサーバ：OpenVPNサーバのグローバルIP
デバイス：TUN
拡張設定：[LZO圧縮を有効にする]をチェック
CA証明書：「ca.crt」を選択
認証：「証明書認証（PKI）を使用」を選択
証明書認証（PKI）/証明書：「client1.crt」を選択
証明書認証（PKI）/秘密鍵：「client1.key」を選択
■詳細設定
追加セキュリティ設定：「TSL-Auth HMAC署名を使用」をチェック
追加セキュリティ設定/共有鍵：「ta.key」を選択

ログからのトラシュー

暗号方式を大文字で記載していた。
cipher AES-256-CBC　→　cipher aes-256-cbc
Fri May 15 10:44:27 2020 TLS Error: cannot locate HMAC in incoming packet from [AF_INET]61.86.178.47:1194

プロトコルのipv4の指定が抜けていた。
udp →　udp4
Fri May 15 10:37:02 2020 Could not determine IPv4/IPv6 protocol. Using AF_INET

サーバを構築する際にいつも忘れてしまうところ。

・SELINUXの無効化
状態確認
getenforce

永久的に無効化
vi /etc/selinux/config
—-
SELINUX=enforcing
—-

・FWの無効化
状態確認
systemctl status iptables
systemctl status firewalld

停止(再起動すると復活する)
/etc/init.d/iptables stop
systemctl stop firewalld

・それでも無理な場合
サービスの状態確認、エラーの場合は問題箇所も表示される
systemctl status [サービス名]

エラーログ確認
vi /var/log/[ログファイル]
jounalctl

名前解決の流れを整理

https://www.xxx.jp というWebサイトにアクセスする場合
①クライアントAは「www.xxx.jp」のIPアドレスを知る為に、PCに設定されたDNSキャッシュサーバに名前解決を依頼する。
②名前解決を依頼された検索用DNSサーバはルートDNSサーバに問い合わせをする。
③ルートDNSサーバ自身は「www.xxx.jp」のIPアドレスは知らないが、「.jp」ドメインを管轄しているDNSサーバBのIPアドレスを知っているのでそのアドレスを返す。
④DNSキャッシュサーバはDNSサーバBに対して問い合わせをする。
⑤DNSサーバB自身は「www.xxx.jp」のIPアドレスは知らないが、「xxx.jp」ドメインを管轄しているDNSサーバCのIPアドレスを知っているのでそのアドレスを返す。
⑥DNSキャッシュサーバはDNSサーバCに対して問い合わせをする。
⑦DNSサーバCは「www.xxx.jp」のIPアドレスを知っているのでそのアドレスを返す。
⑧DNSキャッシュサーバはクライアントAに「www.xxx.jp」のIPアドレスを返す。
⑨DNSキャッシュサーバは「www.xxx.jp」のIPアドレスを元に「https://www.xxx.jp」へアクセスする。

DNSキャッシュサーバのパターン

①ISPが運用するDNSキャッシュサーバを使用する場合
一番スタンダードで特に追加の設定は不要。ONUからIPアドレスを自動取得するとISPのDNSキャッシュサーバも一緒に降ってくる。
②インターネット上のDNSキャッシュサーバを使用する場合
PCにインターネット上のDNSキャッシュサーバのアドレスを手動設定する。有名なDNS1サーバでgoogleの8.8.8.8などがある。
③自前でキャッシュサーバを用意する場合
PCに自前で用意したのDNSキャッシュサーバのアドレスを手動設定する。

named.caについて

自前でキャッシュサーバを用意する場合はLinuxのBIND等を使ってDNSキャッシュサーバを構築する必要がある。

名前解決の流れで記載した通り、DNSキャッシュサーバはルートDNSサーバのに問い合わせを行うのでルートDNSサーバの情報を持っている。デフォルトでは「named.ca」という名前のファイルに記載されていたので中身を見てみる。

; <<>> DiG 9.11.3-RedHat-9.11.3-3.fc27 <<>> +bufsize=1200 +norec @a.root-servers.net
; (2 servers found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 46900
;; flags: qr aa; QUERY: 1, ANSWER: 13, AUTHORITY: 0, ADDITIONAL: 27

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1472
;; QUESTION SECTION:
;.                              IN      NS

;; ANSWER SECTION:
.                       518400  IN      NS      a.root-servers.net.
.                       518400  IN      NS      b.root-servers.net.
.                       518400  IN      NS      c.root-servers.net.
.                       518400  IN      NS      d.root-servers.net.
.                       518400  IN      NS      e.root-servers.net.
.                       518400  IN      NS      f.root-servers.net.
.                       518400  IN      NS      g.root-servers.net.
.                       518400  IN      NS      h.root-servers.net.
.                       518400  IN      NS      i.root-servers.net.
.                       518400  IN      NS      j.root-servers.net.
.                       518400  IN      NS      k.root-servers.net.
.                       518400  IN      NS      l.root-servers.net.
.                       518400  IN      NS      m.root-servers.net.

;; ADDITIONAL SECTION:
a.root-servers.net.     518400  IN      A       198.41.0.4
b.root-servers.net.     518400  IN      A       199.9.14.201
c.root-servers.net.     518400  IN      A       192.33.4.12
d.root-servers.net.     518400  IN      A       199.7.91.13
e.root-servers.net.     518400  IN      A       192.203.230.10
f.root-servers.net.     518400  IN      A       192.5.5.241
g.root-servers.net.     518400  IN      A       192.112.36.4
h.root-servers.net.     518400  IN      A       198.97.190.53
i.root-servers.net.     518400  IN      A       192.36.148.17
j.root-servers.net.     518400  IN      A       192.58.128.30
k.root-servers.net.     518400  IN      A       193.0.14.129
l.root-servers.net.     518400  IN      A       199.7.83.42
m.root-servers.net.     518400  IN      A       202.12.27.33
a.root-servers.net.     518400  IN      AAAA    2001:503:ba3e::2:30
b.root-servers.net.     518400  IN      AAAA    2001:500:200::b
c.root-servers.net.     518400  IN      AAAA    2001:500:2::c
d.root-servers.net.     518400  IN      AAAA    2001:500:2d::d
e.root-servers.net.     518400  IN      AAAA    2001:500:a8::e
f.root-servers.net.     518400  IN      AAAA    2001:500:2f::f
g.root-servers.net.     518400  IN      AAAA    2001:500:12::d0d
h.root-servers.net.     518400  IN      AAAA    2001:500:1::53
i.root-servers.net.     518400  IN      AAAA    2001:7fe::53
j.root-servers.net.     518400  IN      AAAA    2001:503:c27::2:30
k.root-servers.net.     518400  IN      AAAA    2001:7fd::1
l.root-servers.net.     518400  IN      AAAA    2001:500:9f::42
m.root-servers.net.     518400  IN      AAAA    2001:dc3::35

;; Query time: 24 msec
;; SERVER: 198.41.0.4#53(198.41.0.4)
;; WHEN: Thu Apr 05 15:57:34 CEST 2018
;; MSG SIZE  rcvd: 811

A～Mまでの13個のルートDNSサーバのアドレスが記載されている。この情報をもとに冒頭に書いた流れの「www.xxx.jp」の名前解決が出来ていることになる。
ちなみにこの情報は変更されることがあるので、自前でキャッシュサーバを用意する場合は定期的に変更確認をしないといつの間にかインターネット上のWebサイトに繋がらなくなることが考えられる。
因みにこのファイルの最新版は下記のリンクに「named.cache」という名前で存在する。
最新版