Configure OpenVPN Clients to use specific DNS Server

koromicha
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Last Updated:
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Security, HowTos, OpenVPN, VPN
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3 Comments

This is a quick tutorial on how to configure OpenVPN clients to use specific DNS server. OpenVPN server can be configured to enable the clients to use specific DNS server for hostname resolution.

Install and Configure OpenVPN Server

In our previous tutorials, we have covered how to install and configure OpenVPN server

Configuring OpenVPN Clients to use specific DNS Server

To use specific DNS server with OpenVPN clients;

There are various ways in which you can push specific DNS servers for name resolution.

Push DNS addresses to Clients from OpenVPN Server

To configure OpenVPN server to push DNS addresses to clients, edit the OpenVPN server configuration file and add the line;

push "dhcp-option DNS X.X.X.X"

Where X.X.X.X is the DNS server IP address.

You can add multiple DNS server entries;

push "dhcp-option DNS 192.168.58.22"
push "dhcp-option DNS 8.8.8.8"

To specify the DNS domain part;

push "dhcp-option DOMAIN DOMAIN-NAME"

For example;

push "dhcp-option DOMAIN kifarunix-demo.com"

Here is a sample of my OpenVPN server configuration file;

cat /etc/openvpn/server/server.conf

port 1194
proto udp
dev tun
ca ca.crt
cert issued/server.crt
key private/server.key  # This file should be kept secret
dh dh.pem
topology subnet
server 10.8.0.0 255.255.255.0
ifconfig-pool-persist /var/log/openvpn/ipp.txt
push "redirect-gateway def1 bypass-dhcp"
push "dhcp-option DNS 192.168.58.22"
push "dhcp-option DNS 8.8.8.8"
push "dhcp-option DOMAIN kifarunix-demo.com"
client-to-client
keepalive 10 120
tls-auth ta.key 0 # This file is secret
cipher AES-256-CBC
data-ciphers AES-256-CBC
comp-lzo no
persist-key
persist-tun
status /var/log/openvpn/openvpn-status.log
log-append  /var/log/openvpn/openvpn.log
verb 3
explicit-exit-notify 1
auth SHA512

Restart DNS Server;

systemctl restart [email protected]

Define DNS addresses on OpenVPN Client config

If you dont have access to the OpenVPN server to enforce the above configurations, then you can edit your OpenVPN client configuration file and add the lines;

dhcp-option DNS X.X.X.X
dhcp-option DNS DNS-IP-1
dhcp-option DNS DNS-IP-2
push "dhcp-option DOMAIN DOMAIN-NAME"

Here is a sample OpenVPN client;

cat client-1.ovpn

client
tls-client
pull
dev tun
proto udp4
remote 192.168.58.22 1194
resolv-retry infinite
nobind
#user nobody
#group nogroup
persist-key
persist-tun
key-direction 1
remote-cert-tls server
auth-nocache
comp-lzo
verb 3
auth SHA512
cipher AES-256-CBC
data-ciphers AES-256-CBC
comp-lzo no

#
# 2048 bit OpenVPN static key
#
-----BEGIN OpenVPN Static key V1-----
ec31b288a9a3865c4b5f3583b481ff5c
434e957be6569ed573a58a102ce53efc
b9528f15f5412046c5a603e6916b565b
fe2c6a0f955dcec2d3f7e6cec7e373bb
dff40b041f1488d4177c3de04bdff43b
e361eff6328c499621e0846ec72565ef
734fc02e51540d1c5c19102156a080f7
fde124822bf6fc802dff9facf24998de
6f91f081dafcdd28f4bca9223afe694d
12d57beb6aed96753d651a2ca4722214
5fa87829b9f53f2ccb89d9f15112c9cd
3594ead75bc1df737b50188c2829d724
3aff136577b3c79e6f863112aadf5aeb
8b6d53c607874c71104acfa22e587bd3
22b14a2c0a91e15569d99d5e35a52a8b
0aa4f24ccf10d8757dfd75da14fd21ac
-----END OpenVPN Static key V1-----


-----BEGIN CERTIFICATE-----
MIIDSzCCAjOgAwIBAgIUW5NhoHubpdB2QE1IdTqCZeD4CK4wDQYJKoZIhvcNAQEL
BQAwFjEUMBIGA1UEAwwLRWFzeS1SU0EgQ0EwHhcNMjExMTA1MTcxNDQ4WhcNMzEx
MTAzMTcxNDQ4WjAWMRQwEgYDVQQDDAtFYXN5LVJTQSBDQTCCASIwDQYJKoZIhvcN
AQEBBQADggEPADCCAQoCggEBALGvwj57vpugazdMtjIVngKybzapSfT7rm1Rv+d2
SssBwsTf4kDXqfwQiQLPEDo5mpxIO1XBEhsNS3CeBBSfGHgvT3EbiXKLS0mpMiIK
nayJJh2+v3xg+3EU5jemNJ8p3iqsWz566ds/C6haZsp9cM5oGBOOSbHOMJo4S6+6
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nyDQrLtcZiVyoPCJxB41OoTYd1aLDV/7F+A6ShSQSw/04jQq3yoyQd9qMZUfPieE
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BgNVHQ4EFgQUvMfE2qXU2IZw4c5X+i48cGji1/owUQYDVR0jBEowSIAUvMfE2qXU
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ow62PMXOp31ru1vq0ar/BjYE9EhQVEFdErhmc0FMmrkWP7H5rwRX7GO5T3wNfO3q
+rftpJiCVeY4lFWyNuHKZv3n8DtfwOoT5ybpJ31/mn6i/SWfaJa5gY9I8+jh6q7m
bRcTvNQk+G1ApgJZuoV5shAPZg6oJZVvU9q8FryMmcPxB4dTZwA3NIZfjQs8Q7lD
B0/XhJ+bjQvtC2YLfNLZgsEwOrUGs+ZCbL3T1FyLpg==
-----END CERTIFICATE-----


Certificate:
    Data:
        Version: 3 (0x2)
        Serial Number:
            a8:92:f9:c5:d7:40:22:75:38:b8:b6:b6:1e:b1:8c:2c
        Signature Algorithm: sha256WithRSAEncryption
        Issuer: CN=Easy-RSA CA
        Validity
            Not Before: Nov  5 17:20:19 2021 GMT
            Not After : Feb  8 17:20:19 2024 GMT
        Subject: CN=koromicha
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                RSA Public-Key: (2048 bit)
                Modulus:
                    00:d1:f5:5f:c8:1e:6c:c5:35:fe:9a:68:d1:91:2d:
                    cb:11:b3:08:ed:47:3a:b8:32:74:df:f1:b7:78:be:
                    25:fc:95:73:be:6b:de:c8:89:1d:39:5e:72:4d:ea:
                    a3:13:2a:c9:29:44:2e:17:fc:48:d9:6c:8b:2f:ca:
                    a4:e5:90:43:a9:8b:a2:7a:bb:b5:c8:7a:6a:fe:9d:
                    4b:aa:67:78:e8:3f:53:9e:9d:b3:25:77:a1:22:f3:
                    b1:f0:82:97:9e:f5:14:b2:93:de:c5:20:84:05:54:
                    d5:70:ad:d5:4f:41:04:a6:56:04:08:e9:45:ea:eb:
                    c2:00:da:ee:1b:b4:30:74:c5:9e:76:6d:49:0c:8c:
                    7e:45:8a:e5:93:1a:d0:f6:70:1a:73:df:b2:eb:68:
                    2d:7a:1e:68:00:9e:b1:1f:1d:14:75:1b:89:56:b2:
                    e8:8e:84:e6:ea:39:50:93:0d:0e:30:6d:fc:97:3e:
                    6a:66:c3:cc:f3:93:12:5c:38:b4:62:ef:58:7f:a7:
                    70:05:2c:2d:f0:54:5e:7e:7a:98:ea:af:8d:6d:2e:
                    9c:47:80:1f:26:67:b4:2d:44:11:2f:6d:a5:9a:96:
                    7f:b5:ae:f8:48:61:ca:5c:f8:d5:1b:44:40:8b:fc:
                    97:01:5e:15:24:28:c6:24:81:39:d4:e0:3d:1f:81:
                    9a:11
                Exponent: 65537 (0x10001)
        X509v3 extensions:
            X509v3 Basic Constraints: 
                CA:FALSE
            X509v3 Subject Key Identifier: 
                B1:97:65:D8:90:01:7E:57:CA:11:73:4D:E2:E3:83:6F:71:B9:1B:6E
            X509v3 Authority Key Identifier: 
                keyid:BC:C7:C4:DA:A5:D4:D8:86:70:E1:CE:57:FA:2E:3C:70:68:E2:D7:FA
                DirName:/CN=Easy-RSA CA
                serial:5B:93:61:A0:7B:9B:A5:D0:76:40:4D:48:75:3A:82:65:E0:F8:08:AE

            X509v3 Extended Key Usage: 
                TLS Web Client Authentication
            X509v3 Key Usage: 
                Digital Signature
    Signature Algorithm: sha256WithRSAEncryption
         57:ae:78:40:08:84:4f:4a:ec:53:b3:85:96:e8:c9:25:2b:3f:
         37:16:37:53:e4:7b:eb:c5:0b:29:36:75:44:75:cc:47:a2:b1:
         3a:fa:a1:07:88:89:99:b4:6e:21:82:1a:8e:42:1d:6c:b9:b5:
         e2:21:85:55:a8:34:9e:80:52:27:81:c2:f7:af:e7:94:27:bf:
         cb:7c:a2:cf:39:90:95:95:29:75:a1:c7:9c:68:5b:5e:5c:aa:
         81:3d:c7:8a:79:54:9c:bc:9c:73:a2:76:02:56:42:56:4f:82:
         80:23:0e:a3:8d:2f:86:0e:3e:08:7d:a8:b6:55:e7:2a:8f:6b:
         4a:68:99:93:44:57:02:19:11:7d:cc:cf:05:a6:ce:4a:a0:41:
         df:a1:88:8e:b3:0d:f3:67:cf:f9:82:27:41:bc:3b:4e:fb:7f:
         60:e5:43:bb:7f:61:63:71:89:cf:55:fc:ce:82:bb:8c:2a:11:
         9b:e7:e0:97:e3:ba:e0:cd:b0:12:35:56:41:58:62:0d:63:58:
         ec:55:50:2b:82:5a:b5:4f:42:23:c7:e8:e6:8a:91:10:8b:a2:
         40:47:85:ed:98:7f:e5:df:96:06:30:6b:ec:6f:9c:2d:5a:5a:
         0a:71:fb:e2:1d:3e:f6:35:cd:ec:19:9b:67:c2:44:e3:b7:b6:
         9f:81:51:c5
-----BEGIN CERTIFICATE-----
MIIDWDCCAkCgAwIBAgIRAKiS+cXXQCJ1OLi2th6xjCwwDQYJKoZIhvcNAQELBQAw
FjEUMBIGA1UEAwwLRWFzeS1SU0EgQ0EwHhcNMjExMTA1MTcyMDE5WhcNMjQwMjA4
MTcyMDE5WjAUMRIwEAYDVQQDDAlrb3JvbWljaGEwggEiMA0GCSqGSIb3DQEBAQUA
A4IBDwAwggEKAoIBAQDR9V/IHmzFNf6aaNGRLcsRswjtRzq4MnTf8bd4viX8lXO+
a97IiR05XnJN6qMTKskpRC4X/EjZbIsvyqTlkEOpi6J6u7XIemr+nUuqZ3joP1Oe
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bUkMjH5FiuWTGtD2cBpz37LraC16HmgAnrEfHRR1G4lWsuiOhObqOVCTDQ4wbfyX
Pmpmw8zzkxJcOLRi71h/p3AFLC3wVF5+epjqr41tLpxHgB8mZ7QtRBEvbaWaln+1
rvhIYcpc+NUbRECL/JcBXhUkKMYkgTnU4D0fgZoRAgMBAAGjgaIwgZ8wCQYDVR0T
BAIwADAdBgNVHQ4EFgQUsZdl2JABflfKEXNN4uODb3G5G24wUQYDVR0jBEowSIAU
vMfE2qXU2IZw4c5X+i48cGji1/qhGqQYMBYxFDASBgNVBAMMC0Vhc3ktUlNBIENB
ghRbk2Gge5ul0HZATUh1OoJl4PgIrjATBgNVHSUEDDAKBggrBgEFBQcDAjALBgNV
HQ8EBAMCB4AwDQYJKoZIhvcNAQELBQADggEBAFeueEAIhE9K7FOzhZboySUrPzcW
N1Pke+vFCyk2dUR1zEeisTr6oQeIiZm0biGCGo5CHWy5teIhhVWoNJ6AUieBwvev
55Qnv8t8os85kJWVKXWhx5xoW15cqoE9x4p5VJy8nHOidgJWQlZPgoAjDqONL4YO
Pgh9qLZV5yqPa0pomZNEVwIZEX3MzwWmzkqgQd+hiI6zDfNnz/mCJ0G8O077f2Dl
Q7t/YWNxic9V/M6Cu4wqEZvn4JfjuuDNsBI1VkFYYg1jWOxVUCuCWrVPQiPH6OaK
kRCLokBHhe2Yf+XflgYwa+xvnC1aWgpx++IdPvY1zewZm2fCROO3tp+BUcU=
-----END CERTIFICATE-----


-----BEGIN PRIVATE KEY-----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4OIhDq5puDT+b5fhhYBRkw/gVkhQSEtgigoyjb7FGCIoVlvGkHAVZ616oS9Pvfk4
EkzLqnOaocL8F+2GfcblBnARE7lrlMPP+EdsYGiGqp7+tnGtwO6BNYC+ZjMKKg46
w3tYbNw6RwzgC+f7UCLUfpBaMfnnS0zRBRfi+OxEcQKBgEMEes7DT5sqoQkam9lk
AmP8NK+eAoB7RWk8A1ADBlz48xmIH/lR99su9bWWd0xthYuBvx3ZpPRTqp0Z2ehm
7w3jnw+A7BZn1/gmcXLCXexQl+tn0nfm87xpwXCDmHjZzdldzLMpjOMHZDmOcufN
y30Rsmt3vdeo5Rv+whSSypnq
-----END PRIVATE KEY-----

Use specific DNS Server with OpenVPN Clients

So depending on the method you used above to define the DNS server address you can proceed as follows.

In this tutorial, we are using a Linux system, specifically, Debian 11/Rocky Linux 8 as our OpenVPN clients for demonstration purposes.

On Ubuntu/Debian Systems:

install openresol package.On Ubuntu/Debian systems;

apt install openresolv

Next, edit the OpenVPN client configuration file;

vim client-1.ovpn

and add the lines below;

script-security 2
up /etc/openvpn/update-resolv-conf
down /etc/openvpn/update-resolv-conf

See my sample updated OpenVPN client configuration file;

cat client-1.ovpn

client
tls-client
pull
dev tun
proto udp4
remote 192.168.58.22 1194
resolv-retry infinite
nobind
persist-key
persist-tun
key-direction 1
remote-cert-tls server
auth-nocache
comp-lzo
verb 3
auth SHA512
cipher AES-256-CBC
data-ciphers AES-256-CBC
comp-lzo no
script-security 2
up /etc/openvpn/update-resolv-conf
down /etc/openvpn/update-resolv-conf

-----BEGIN OpenVPN Static key V1-----
ec31b288a9a3865c4b5f3583b481ff5c
434e957be6569ed573a58a102ce53efc
b9528f15f5412046c5a603e6916b565b
fe2c6a0f955dcec2d3f7e6cec7e373bb
dff40b041f1488d4177c3de04bdff43b
e361eff6328c499621e0846ec72565ef
734fc02e51540d1c5c19102156a080f7
fde124822bf6fc802dff9facf24998de
6f91f081dafcdd28f4bca9223afe694d
12d57beb6aed96753d651a2ca4722214
5fa87829b9f53f2ccb89d9f15112c9cd
3594ead75bc1df737b50188c2829d724
3aff136577b3c79e6f863112aadf5aeb
8b6d53c607874c71104acfa22e587bd3
22b14a2c0a91e15569d99d5e35a52a8b
0aa4f24ccf10d8757dfd75da14fd21ac
-----END OpenVPN Static key V1-----


-----BEGIN CERTIFICATE-----
MIIDSzCCAjOgAwIBAgIUW5NhoHubpdB2QE1IdTqCZeD4CK4wDQYJKoZIhvcNAQEL
BQAwFjEUMBIGA1UEAwwLRWFzeS1SU0EgQ0EwHhcNMjExMTA1MTcxNDQ4WhcNMzEx
MTAzMTcxNDQ4WjAWMRQwEgYDVQQDDAtFYXN5LVJTQSBDQTCCASIwDQYJKoZIhvcN
AQEBBQADggEPADCCAQoCggEBALGvwj57vpugazdMtjIVngKybzapSfT7rm1Rv+d2
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BgNVHQ4EFgQUvMfE2qXU2IZw4c5X+i48cGji1/owUQYDVR0jBEowSIAUvMfE2qXU
2IZw4c5X+i48cGji1/qhGqQYMBYxFDASBgNVBAMMC0Vhc3ktUlNBIENBghRbk2Gg
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hkiG9w0BAQsFAAOCAQEAn5mckexf90rXn/xjzhKSbc2pNarQJ/YcmQ5xpRwv8D6x
GQieEk9BB8iWzaufH0cW+LI80zZYpjMg1qygKDoPIRryn0MVsr03XRCxnQRlkC7f
ow62PMXOp31ru1vq0ar/BjYE9EhQVEFdErhmc0FMmrkWP7H5rwRX7GO5T3wNfO3q
+rftpJiCVeY4lFWyNuHKZv3n8DtfwOoT5ybpJ31/mn6i/SWfaJa5gY9I8+jh6q7m
bRcTvNQk+G1ApgJZuoV5shAPZg6oJZVvU9q8FryMmcPxB4dTZwA3NIZfjQs8Q7lD
B0/XhJ+bjQvtC2YLfNLZgsEwOrUGs+ZCbL3T1FyLpg==
-----END CERTIFICATE-----


Certificate:
    Data:
        Version: 3 (0x2)
        Serial Number:
            a8:92:f9:c5:d7:40:22:75:38:b8:b6:b6:1e:b1:8c:2c
        Signature Algorithm: sha256WithRSAEncryption
        Issuer: CN=Easy-RSA CA
        Validity
            Not Before: Nov  5 17:20:19 2021 GMT
            Not After : Feb  8 17:20:19 2024 GMT
        Subject: CN=koromicha
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                RSA Public-Key: (2048 bit)
                Modulus:
                    00:d1:f5:5f:c8:1e:6c:c5:35:fe:9a:68:d1:91:2d:
                    cb:11:b3:08:ed:47:3a:b8:32:74:df:f1:b7:78:be:
                    25:fc:95:73:be:6b:de:c8:89:1d:39:5e:72:4d:ea:
                    a3:13:2a:c9:29:44:2e:17:fc:48:d9:6c:8b:2f:ca:
                    a4:e5:90:43:a9:8b:a2:7a:bb:b5:c8:7a:6a:fe:9d:
                    4b:aa:67:78:e8:3f:53:9e:9d:b3:25:77:a1:22:f3:
                    b1:f0:82:97:9e:f5:14:b2:93:de:c5:20:84:05:54:
                    d5:70:ad:d5:4f:41:04:a6:56:04:08:e9:45:ea:eb:
                    c2:00:da:ee:1b:b4:30:74:c5:9e:76:6d:49:0c:8c:
                    7e:45:8a:e5:93:1a:d0:f6:70:1a:73:df:b2:eb:68:
                    2d:7a:1e:68:00:9e:b1:1f:1d:14:75:1b:89:56:b2:
                    e8:8e:84:e6:ea:39:50:93:0d:0e:30:6d:fc:97:3e:
                    6a:66:c3:cc:f3:93:12:5c:38:b4:62:ef:58:7f:a7:
                    70:05:2c:2d:f0:54:5e:7e:7a:98:ea:af:8d:6d:2e:
                    9c:47:80:1f:26:67:b4:2d:44:11:2f:6d:a5:9a:96:
                    7f:b5:ae:f8:48:61:ca:5c:f8:d5:1b:44:40:8b:fc:
                    97:01:5e:15:24:28:c6:24:81:39:d4:e0:3d:1f:81:
                    9a:11
                Exponent: 65537 (0x10001)
        X509v3 extensions:
            X509v3 Basic Constraints: 
                CA:FALSE
            X509v3 Subject Key Identifier: 
                B1:97:65:D8:90:01:7E:57:CA:11:73:4D:E2:E3:83:6F:71:B9:1B:6E
            X509v3 Authority Key Identifier: 
                keyid:BC:C7:C4:DA:A5:D4:D8:86:70:E1:CE:57:FA:2E:3C:70:68:E2:D7:FA
                DirName:/CN=Easy-RSA CA
                serial:5B:93:61:A0:7B:9B:A5:D0:76:40:4D:48:75:3A:82:65:E0:F8:08:AE

            X509v3 Extended Key Usage: 
                TLS Web Client Authentication
            X509v3 Key Usage: 
                Digital Signature
    Signature Algorithm: sha256WithRSAEncryption
         57:ae:78:40:08:84:4f:4a:ec:53:b3:85:96:e8:c9:25:2b:3f:
         37:16:37:53:e4:7b:eb:c5:0b:29:36:75:44:75:cc:47:a2:b1:
         3a:fa:a1:07:88:89:99:b4:6e:21:82:1a:8e:42:1d:6c:b9:b5:
         e2:21:85:55:a8:34:9e:80:52:27:81:c2:f7:af:e7:94:27:bf:
         cb:7c:a2:cf:39:90:95:95:29:75:a1:c7:9c:68:5b:5e:5c:aa:
         81:3d:c7:8a:79:54:9c:bc:9c:73:a2:76:02:56:42:56:4f:82:
         80:23:0e:a3:8d:2f:86:0e:3e:08:7d:a8:b6:55:e7:2a:8f:6b:
         4a:68:99:93:44:57:02:19:11:7d:cc:cf:05:a6:ce:4a:a0:41:
         df:a1:88:8e:b3:0d:f3:67:cf:f9:82:27:41:bc:3b:4e:fb:7f:
         60:e5:43:bb:7f:61:63:71:89:cf:55:fc:ce:82:bb:8c:2a:11:
         9b:e7:e0:97:e3:ba:e0:cd:b0:12:35:56:41:58:62:0d:63:58:
         ec:55:50:2b:82:5a:b5:4f:42:23:c7:e8:e6:8a:91:10:8b:a2:
         40:47:85:ed:98:7f:e5:df:96:06:30:6b:ec:6f:9c:2d:5a:5a:
         0a:71:fb:e2:1d:3e:f6:35:cd:ec:19:9b:67:c2:44:e3:b7:b6:
         9f:81:51:c5
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----


-----BEGIN PRIVATE KEY-----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-----END PRIVATE KEY-----

Connect client to VPN;

openvpn client-1.ovpn

2021-11-08 14:25:09 WARNING: Compression for receiving enabled. Compression has been used in the past to break encryption. Sent packets are not compressed unless "allow-compression yes" is also set.
2021-11-08 14:25:09 OpenVPN 2.5.1 x86_64-pc-linux-gnu [SSL (OpenSSL)] [LZO] [LZ4] [EPOLL] [PKCS11] [MH/PKTINFO] [AEAD] built on May 14 2021
2021-11-08 14:25:09 library versions: OpenSSL 1.1.1k  25 Mar 2021, LZO 2.10
2021-11-08 14:25:09 NOTE: the current --script-security setting may allow this configuration to call user-defined scripts
2021-11-08 14:25:09 Outgoing Control Channel Authentication: Using 512 bit message hash 'SHA512' for HMAC authentication
2021-11-08 14:25:09 Incoming Control Channel Authentication: Using 512 bit message hash 'SHA512' for HMAC authentication
2021-11-08 14:25:09 TCP/UDP: Preserving recently used remote address: [AF_INET]192.168.58.22:1194
2021-11-08 14:25:09 Socket Buffers: R=[212992->212992] S=[212992->212992]
2021-11-08 14:25:09 UDPv4 link local: (not bound)
2021-11-08 14:25:09 UDPv4 link remote: [AF_INET]192.168.58.22:1194
2021-11-08 14:25:09 TLS: Initial packet from [AF_INET]192.168.58.22:1194, sid=0a6596f7 2db76aa3
2021-11-08 14:25:09 VERIFY OK: depth=1, CN=Easy-RSA CA
2021-11-08 14:25:09 VERIFY KU OK
2021-11-08 14:25:09 Validating certificate extended key usage
2021-11-08 14:25:09 ++ Certificate has EKU (str) TLS Web Server Authentication, expects TLS Web Server Authentication
2021-11-08 14:25:09 VERIFY EKU OK
2021-11-08 14:25:09 VERIFY OK: depth=0, CN=server
2021-11-08 14:25:09 Control Channel: TLSv1.3, cipher TLSv1.3 TLS_AES_256_GCM_SHA384, 2048 bit RSA
2021-11-08 14:25:09 [server] Peer Connection Initiated with [AF_INET]192.168.58.22:1194
2021-11-08 14:25:09 PUSH: Received control message: 'PUSH_REPLY,redirect-gateway def1 bypass-dhcp,dhcp-option DNS 192.168.58.22,dhcp-option DNS 8.8.8.8,dhcp-option DOMAIN kifarunix-demo.com,route-gateway 10.8.0.1,topology subnet,ping 10,ping-restart 120,ifconfig 10.8.0.2 255.255.255.0,peer-id 0,cipher AES-256-CBC'
2021-11-08 14:25:09 OPTIONS IMPORT: timers and/or timeouts modified
2021-11-08 14:25:09 OPTIONS IMPORT: --ifconfig/up options modified
2021-11-08 14:25:09 OPTIONS IMPORT: route options modified
2021-11-08 14:25:09 OPTIONS IMPORT: route-related options modified
2021-11-08 14:25:09 OPTIONS IMPORT: --ip-win32 and/or --dhcp-option options modified
2021-11-08 14:25:09 OPTIONS IMPORT: peer-id set
2021-11-08 14:25:09 OPTIONS IMPORT: adjusting link_mtu to 1625
2021-11-08 14:25:09 OPTIONS IMPORT: data channel crypto options modified
2021-11-08 14:25:09 Outgoing Data Channel: Cipher 'AES-256-CBC' initialized with 256 bit key
2021-11-08 14:25:09 Outgoing Data Channel: Using 512 bit message hash 'SHA512' for HMAC authentication
2021-11-08 14:25:09 Incoming Data Channel: Cipher 'AES-256-CBC' initialized with 256 bit key
2021-11-08 14:25:09 Incoming Data Channel: Using 512 bit message hash 'SHA512' for HMAC authentication
2021-11-08 14:25:09 net_route_v4_best_gw query: dst 0.0.0.0
2021-11-08 14:25:09 net_route_v4_best_gw result: via 10.0.2.2 dev enp0s3
2021-11-08 14:25:09 ROUTE_GATEWAY 10.0.2.2/255.255.255.0 IFACE=enp0s3 HWADDR=08:00:27:36:23:40
2021-11-08 14:25:09 TUN/TAP device tun0 opened
2021-11-08 14:25:09 net_iface_mtu_set: mtu 1500 for tun0
2021-11-08 14:25:09 net_iface_up: set tun0 up
2021-11-08 14:25:09 net_addr_v4_add: 10.8.0.2/24 dev tun0
2021-11-08 14:25:09 /etc/openvpn/update-resolv-conf tun0 1500 1625 10.8.0.2 255.255.255.0 init
dhcp-option DNS 192.168.58.22
dhcp-option DNS 8.8.8.8
dhcp-option DOMAIN kifarunix-demo.com
2021-11-08 14:25:10 net_route_v4_add: 192.168.58.22/32 via 10.0.2.2 dev [NULL] table 0 metric -1
2021-11-08 14:25:10 net_route_v4_add: 0.0.0.0/1 via 10.8.0.1 dev [NULL] table 0 metric -1
2021-11-08 14:25:10 net_route_v4_add: 128.0.0.0/1 via 10.8.0.1 dev [NULL] table 0 metric -1
2021-11-08 14:25:10 Initialization Sequence Completed

This updates the /etc/resolv.conf file with your custom DNS entries;

cat /etc/resolv.conf
# Generated by resolvconf
search kifarunix-demo.com
nameserver 192.168.58.22
nameserver 8.8.8.8

My internal DNS resolution;

dig debian11.kifarunix-demo.com +short
192.168.59.14

Refer to our DNS guide;

Configure BIND DNS Server using Webmin on Debian 11

On CentOS/RHEL/Rocky Linux:

install update-systemd-resolved

git clone https://github.com/jonathanio/update-systemd-resolved.git
cd update-systemd-resolved
make

Sample output;

Successfully installed update-systemd-resolved to /etc/openvpn/scripts/update-systemd-resolved. Now would be a good time to update /etc/nsswitch.conf: # Use systemd-resolved first, then fall back to /etc/resolv.conf hosts: files resolve dns myhostname # Use /etc/resolv.conf first, then fall back to systemd-resolved hosts: files dns resolve myhostname You should also update your OpenVPN configuration: setenv PATH /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin script-security 2 up /etc/openvpn/scripts/update-systemd-resolved up-restart down /etc/openvpn/scripts/update-systemd-resolved down-pre or pass –config /etc/openvpn/scripts/update-systemd-resolved.conf in addition to any other –config arguments to your openvpn command.

Next, enable systemd-resolved.service.

systemctl enable --now systemd-resolved.service

Update the /etc/nsswitch.conf file to look up DNS via the resolve (systemd-resolved.service) service. (Use /etc/resolv.conf first, then fall back to systemd-resolved)

sed -i '/hosts:/s/dns/dns resolve/' /etc/nsswitch.conf

Next, update the client configuration file to include the lines;

setenv PATH /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
script-security 2
up /etc/openvpn/scripts/update-systemd-resolved
up-restart
down /etc/openvpn/scripts/update-systemd-resolved
down-pre

And this is how my sample config looks like;

cat client-1.ovpn

client
tls-client
pull
dev tun
proto udp4
remote 192.168.58.22 1194
resolv-retry infinite
nobind
persist-key
persist-tun
key-direction 1
remote-cert-tls server
auth-nocache
comp-lzo
verb 3
auth SHA512
cipher AES-256-CBC
comp-lzo no
setenv PATH /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
script-security 2
up /etc/openvpn/scripts/update-systemd-resolved
up-restart
down /etc/openvpn/scripts/update-systemd-resolved
down-pre

#
# 2048 bit OpenVPN static key
#
-----BEGIN OpenVPN Static key V1-----
ec31b288a9a3865c4b5f3583b481ff5c
434e957be6569ed573a58a102ce53efc
b9528f15f5412046c5a603e6916b565b
fe2c6a0f955dcec2d3f7e6cec7e373bb
dff40b041f1488d4177c3de04bdff43b
e361eff6328c499621e0846ec72565ef
734fc02e51540d1c5c19102156a080f7
fde124822bf6fc802dff9facf24998de
6f91f081dafcdd28f4bca9223afe694d
12d57beb6aed96753d651a2ca4722214
5fa87829b9f53f2ccb89d9f15112c9cd
3594ead75bc1df737b50188c2829d724
3aff136577b3c79e6f863112aadf5aeb
8b6d53c607874c71104acfa22e587bd3
22b14a2c0a91e15569d99d5e35a52a8b
0aa4f24ccf10d8757dfd75da14fd21ac
-----END OpenVPN Static key V1-----


-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----


Certificate:
    Data:
        Version: 3 (0x2)
        Serial Number:
            a8:92:f9:c5:d7:40:22:75:38:b8:b6:b6:1e:b1:8c:2c
        Signature Algorithm: sha256WithRSAEncryption
        Issuer: CN=Easy-RSA CA
        Validity
            Not Before: Nov  5 17:20:19 2021 GMT
            Not After : Feb  8 17:20:19 2024 GMT
        Subject: CN=koromicha
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                RSA Public-Key: (2048 bit)
                Modulus:
                    00:d1:f5:5f:c8:1e:6c:c5:35:fe:9a:68:d1:91:2d:
                    cb:11:b3:08:ed:47:3a:b8:32:74:df:f1:b7:78:be:
                    25:fc:95:73:be:6b:de:c8:89:1d:39:5e:72:4d:ea:
                    a3:13:2a:c9:29:44:2e:17:fc:48:d9:6c:8b:2f:ca:
                    a4:e5:90:43:a9:8b:a2:7a:bb:b5:c8:7a:6a:fe:9d:
                    4b:aa:67:78:e8:3f:53:9e:9d:b3:25:77:a1:22:f3:
                    b1:f0:82:97:9e:f5:14:b2:93:de:c5:20:84:05:54:
                    d5:70:ad:d5:4f:41:04:a6:56:04:08:e9:45:ea:eb:
                    c2:00:da:ee:1b:b4:30:74:c5:9e:76:6d:49:0c:8c:
                    7e:45:8a:e5:93:1a:d0:f6:70:1a:73:df:b2:eb:68:
                    2d:7a:1e:68:00:9e:b1:1f:1d:14:75:1b:89:56:b2:
                    e8:8e:84:e6:ea:39:50:93:0d:0e:30:6d:fc:97:3e:
                    6a:66:c3:cc:f3:93:12:5c:38:b4:62:ef:58:7f:a7:
                    70:05:2c:2d:f0:54:5e:7e:7a:98:ea:af:8d:6d:2e:
                    9c:47:80:1f:26:67:b4:2d:44:11:2f:6d:a5:9a:96:
                    7f:b5:ae:f8:48:61:ca:5c:f8:d5:1b:44:40:8b:fc:
                    97:01:5e:15:24:28:c6:24:81:39:d4:e0:3d:1f:81:
                    9a:11
                Exponent: 65537 (0x10001)
        X509v3 extensions:
            X509v3 Basic Constraints: 
                CA:FALSE
            X509v3 Subject Key Identifier: 
                B1:97:65:D8:90:01:7E:57:CA:11:73:4D:E2:E3:83:6F:71:B9:1B:6E
            X509v3 Authority Key Identifier: 
                keyid:BC:C7:C4:DA:A5:D4:D8:86:70:E1:CE:57:FA:2E:3C:70:68:E2:D7:FA
                DirName:/CN=Easy-RSA CA
                serial:5B:93:61:A0:7B:9B:A5:D0:76:40:4D:48:75:3A:82:65:E0:F8:08:AE

            X509v3 Extended Key Usage: 
                TLS Web Client Authentication
            X509v3 Key Usage: 
                Digital Signature
    Signature Algorithm: sha256WithRSAEncryption
         57:ae:78:40:08:84:4f:4a:ec:53:b3:85:96:e8:c9:25:2b:3f:
         37:16:37:53:e4:7b:eb:c5:0b:29:36:75:44:75:cc:47:a2:b1:
         3a:fa:a1:07:88:89:99:b4:6e:21:82:1a:8e:42:1d:6c:b9:b5:
         e2:21:85:55:a8:34:9e:80:52:27:81:c2:f7:af:e7:94:27:bf:
         cb:7c:a2:cf:39:90:95:95:29:75:a1:c7:9c:68:5b:5e:5c:aa:
         81:3d:c7:8a:79:54:9c:bc:9c:73:a2:76:02:56:42:56:4f:82:
         80:23:0e:a3:8d:2f:86:0e:3e:08:7d:a8:b6:55:e7:2a:8f:6b:
         4a:68:99:93:44:57:02:19:11:7d:cc:cf:05:a6:ce:4a:a0:41:
         df:a1:88:8e:b3:0d:f3:67:cf:f9:82:27:41:bc:3b:4e:fb:7f:
         60:e5:43:bb:7f:61:63:71:89:cf:55:fc:ce:82:bb:8c:2a:11:
         9b:e7:e0:97:e3:ba:e0:cd:b0:12:35:56:41:58:62:0d:63:58:
         ec:55:50:2b:82:5a:b5:4f:42:23:c7:e8:e6:8a:91:10:8b:a2:
         40:47:85:ed:98:7f:e5:df:96:06:30:6b:ec:6f:9c:2d:5a:5a:
         0a:71:fb:e2:1d:3e:f6:35:cd:ec:19:9b:67:c2:44:e3:b7:b6:
         9f:81:51:c5
-----BEGIN CERTIFICATE-----
MIIDWDCCAkCgAwIBAgIRAKiS+cXXQCJ1OLi2th6xjCwwDQYJKoZIhvcNAQELBQAw
FjEUMBIGA1UEAwwLRWFzeS1SU0EgQ0EwHhcNMjExMTA1MTcyMDE5WhcNMjQwMjA4
MTcyMDE5WjAUMRIwEAYDVQQDDAlrb3JvbWljaGEwggEiMA0GCSqGSIb3DQEBAQUA
A4IBDwAwggEKAoIBAQDR9V/IHmzFNf6aaNGRLcsRswjtRzq4MnTf8bd4viX8lXO+
a97IiR05XnJN6qMTKskpRC4X/EjZbIsvyqTlkEOpi6J6u7XIemr+nUuqZ3joP1Oe
nbMld6Ei87Hwgpee9RSyk97FIIQFVNVwrdVPQQSmVgQI6UXq68IA2u4btDB0xZ52
bUkMjH5FiuWTGtD2cBpz37LraC16HmgAnrEfHRR1G4lWsuiOhObqOVCTDQ4wbfyX
Pmpmw8zzkxJcOLRi71h/p3AFLC3wVF5+epjqr41tLpxHgB8mZ7QtRBEvbaWaln+1
rvhIYcpc+NUbRECL/JcBXhUkKMYkgTnU4D0fgZoRAgMBAAGjgaIwgZ8wCQYDVR0T
BAIwADAdBgNVHQ4EFgQUsZdl2JABflfKEXNN4uODb3G5G24wUQYDVR0jBEowSIAU
vMfE2qXU2IZw4c5X+i48cGji1/qhGqQYMBYxFDASBgNVBAMMC0Vhc3ktUlNBIENB
ghRbk2Gge5ul0HZATUh1OoJl4PgIrjATBgNVHSUEDDAKBggrBgEFBQcDAjALBgNV
HQ8EBAMCB4AwDQYJKoZIhvcNAQELBQADggEBAFeueEAIhE9K7FOzhZboySUrPzcW
N1Pke+vFCyk2dUR1zEeisTr6oQeIiZm0biGCGo5CHWy5teIhhVWoNJ6AUieBwvev
55Qnv8t8os85kJWVKXWhx5xoW15cqoE9x4p5VJy8nHOidgJWQlZPgoAjDqONL4YO
Pgh9qLZV5yqPa0pomZNEVwIZEX3MzwWmzkqgQd+hiI6zDfNnz/mCJ0G8O077f2Dl
Q7t/YWNxic9V/M6Cu4wqEZvn4JfjuuDNsBI1VkFYYg1jWOxVUCuCWrVPQiPH6OaK
kRCLokBHhe2Yf+XflgYwa+xvnC1aWgpx++IdPvY1zewZm2fCROO3tp+BUcU=
-----END CERTIFICATE-----


-----BEGIN PRIVATE KEY-----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-----END PRIVATE KEY-----

Connecting to the VPN;

openvpn client-1.ovpn

Tue Nov  9 00:02:52 2021 OpenVPN 2.4.11 x86_64-redhat-linux-gnu [SSL (OpenSSL)] [LZO] [LZ4] [EPOLL] [PKCS11] [MH/PKTINFO] [AEAD] built on Apr 21 2021
Tue Nov  9 00:02:52 2021 library versions: OpenSSL 1.1.1g FIPS  21 Apr 2020, LZO 2.08
Tue Nov  9 00:02:52 2021 NOTE: the current --script-security setting may allow this configuration to call user-defined scripts
Tue Nov  9 00:02:52 2021 Outgoing Control Channel Authentication: Using 512 bit message hash 'SHA512' for HMAC authentication
Tue Nov  9 00:02:52 2021 Incoming Control Channel Authentication: Using 512 bit message hash 'SHA512' for HMAC authentication
Tue Nov  9 00:02:52 2021 TCP/UDP: Preserving recently used remote address: [AF_INET]192.168.58.22:1194
Tue Nov  9 00:02:52 2021 Socket Buffers: R=[212992->212992] S=[212992->212992]
Tue Nov  9 00:02:52 2021 UDPv4 link local: (not bound)
Tue Nov  9 00:02:52 2021 UDPv4 link remote: [AF_INET]192.168.58.22:1194
Tue Nov  9 00:02:52 2021 TLS: Initial packet from [AF_INET]192.168.58.22:1194, sid=f89234f0 4a96fc1e
Tue Nov  9 00:02:52 2021 VERIFY OK: depth=1, CN=Easy-RSA CA
Tue Nov  9 00:02:52 2021 VERIFY KU OK
Tue Nov  9 00:02:52 2021 Validating certificate extended key usage
Tue Nov  9 00:02:52 2021 ++ Certificate has EKU (str) TLS Web Server Authentication, expects TLS Web Server Authentication
Tue Nov  9 00:02:52 2021 VERIFY EKU OK
Tue Nov  9 00:02:52 2021 VERIFY OK: depth=0, CN=server
Tue Nov  9 00:02:52 2021 Control Channel: TLSv1.3, cipher TLSv1.3 TLS_AES_256_GCM_SHA384, 2048 bit RSA
Tue Nov  9 00:02:52 2021 [server] Peer Connection Initiated with [AF_INET]192.168.58.22:1194
Tue Nov  9 00:02:53 2021 SENT CONTROL [server]: 'PUSH_REQUEST' (status=1)
Tue Nov  9 00:02:53 2021 PUSH: Received control message: 'PUSH_REPLY,redirect-gateway def1 bypass-dhcp,dhcp-option DNS 192.168.58.22,dhcp-option DNS 8.8.8.8,dhcp-option DOMAIN kifarunix-demo.com,route-gateway 10.8.0.1,topology subnet,ping 10,ping-restart 120,ifconfig 10.8.0.2 255.255.255.0,peer-id 0,cipher AES-256-CBC'
Tue Nov  9 00:02:53 2021 OPTIONS IMPORT: timers and/or timeouts modified
Tue Nov  9 00:02:53 2021 OPTIONS IMPORT: --ifconfig/up options modified
Tue Nov  9 00:02:53 2021 OPTIONS IMPORT: route options modified
Tue Nov  9 00:02:53 2021 OPTIONS IMPORT: route-related options modified
Tue Nov  9 00:02:53 2021 OPTIONS IMPORT: --ip-win32 and/or --dhcp-option options modified
Tue Nov  9 00:02:53 2021 OPTIONS IMPORT: peer-id set
Tue Nov  9 00:02:53 2021 OPTIONS IMPORT: adjusting link_mtu to 1625
Tue Nov  9 00:02:53 2021 OPTIONS IMPORT: data channel crypto options modified
Tue Nov  9 00:02:53 2021 Outgoing Data Channel: Cipher 'AES-256-CBC' initialized with 256 bit key
Tue Nov  9 00:02:53 2021 Outgoing Data Channel: Using 512 bit message hash 'SHA512' for HMAC authentication
Tue Nov  9 00:02:53 2021 Incoming Data Channel: Cipher 'AES-256-CBC' initialized with 256 bit key
Tue Nov  9 00:02:53 2021 Incoming Data Channel: Using 512 bit message hash 'SHA512' for HMAC authentication
Tue Nov  9 00:02:53 2021 ROUTE_GATEWAY 10.0.2.2/255.255.255.0 IFACE=enp0s3 HWADDR=08:00:27:3e:fe:0e
Tue Nov  9 00:02:53 2021 TUN/TAP device tun0 opened
Tue Nov  9 00:02:53 2021 TUN/TAP TX queue length set to 100
Tue Nov  9 00:02:53 2021 /sbin/ip link set dev tun0 up mtu 1500
Tue Nov  9 00:02:53 2021 /sbin/ip addr add dev tun0 10.8.0.2/24 broadcast 10.8.0.255
Tue Nov  9 00:02:53 2021 /etc/openvpn/scripts/update-systemd-resolved tun0 1500 1605 10.8.0.2 255.255.255.0 init
<14>Nov  9 00:02:53 update-systemd-resolved: Link 'tun0' coming up
<14>Nov  9 00:02:53 update-systemd-resolved: Adding IPv4 DNS Server 192.168.58.22
<14>Nov  9 00:02:53 update-systemd-resolved: Adding IPv4 DNS Server 8.8.8.8
<14>Nov  9 00:02:53 update-systemd-resolved: Adding DNS Domain kifarunix-demo.com
<14>Nov  9 00:02:53 update-systemd-resolved: SetLinkDNS(22 2 2 4 192 168 58 22 2 4 8 8 8 8)
<14>Nov  9 00:02:53 update-systemd-resolved: SetLinkDomains(22 1 kifarunix-demo.com false)
Tue Nov  9 00:02:53 2021 /sbin/ip route add 192.168.58.22/32 via 10.0.2.2
Tue Nov  9 00:02:53 2021 /sbin/ip route add 0.0.0.0/1 via 10.8.0.1
Tue Nov  9 00:02:53 2021 /sbin/ip route add 128.0.0.0/1 via 10.8.0.1
Tue Nov  9 00:02:53 2021 Initialization Sequence Completed

Your local DNS should now be working when connected to VPN.

Read more about DNS leakage.

Other Tutorials

Make Permanent DNS Changes on resolv.conf in Linux

Easily Install and Setup PowerDNS Admin on Ubuntu 20.04

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koromicha
I am the Co-founder of Kifarunix.com, Linux and the whole FOSS enthusiast, Linux System Admin and a Blue Teamer who loves to share technological tips and hacks with others as a way of sharing knowledge as: "In vain have you acquired knowledge if you have not imparted it to others".

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3 thoughts on “Configure OpenVPN Clients to use specific DNS Server”

  3. Thank you for this information. This worked great for my Windows client but I could not get it to work for my Ubuntu Desktop 22.04 client. After trying lots of things, I was able to resolve the issue by editing the file /etc/nsswitch.conf and moving ‘dns’ ahead of ‘mdns’, ‘NOTFOUND’, etc. Perhaps it was unique to my environment, or something else that actually resolved the issue, but at least now it is working.

    Reply

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