Bad DNS when VPN on computer is enabled

Installing and Using OpenWrt
1

PROBLEM
When the VPN is enabled on my computer (not on the router), DNS look-ups are unreliable and vary by browser. In browser A, they never fail; in browser B, they fail with some sites; in browser C (my preferred browser), they fail all the time.

I want DNS on my computer to go to the VPN's service (Mullvad). Other devices on the network should use 9.9.9.9 or similar so that my ISP does not see the look-ups.

This problem occurs whether or not the AP is running.

What must I do to get reliable DNS look-ups when the VPN is enabled on my computer?

BACKGROUND
Until today, I had a Netgear router with OEM firmware and a Cudy WR3000S running stock OpenWrt as a wired/wireless "dumb access point". Today, I replaced the Netgear router with another Cudy WR3000S, and I changed some configuration settings in the dumb AP so that the main router and the AP would function as a single network.

My testing suggests that this set-up is working well, although I have to figure out some things yet (how to get NTP working, how to get fast roaming working).

The one big problem so far is with DNS. I have searched for solutions but mostly found advice to change more than I believe I should have to change (dnsmasq, DHCP, firewall, routing). Is there simple way to do what I need?

CONFIGURATION
This is my first time sharing this information. I hope that it is helpful and that I have redacted appropriately. (I do not know now to tell a public IP address from a private IP address.) Suggestions for changes unrelated to this inquiry are welcome. This is my first experience with OpenWrt. I am not very knowledgeable about networks.

root@Kindness:~# ubus call system board
{
	"kernel": "6.6.73",
	"hostname": "Kindness",
	"system": "ARMv8 Processor rev 4",
	"model": "Cudy WR3000S v1",
	"board_name": "cudy,wr3000s-v1",
	"rootfs_type": "squashfs",
	"release": {
		"distribution": "OpenWrt",
		"version": "24.10.0",
		"revision": "r28427-6df0e3d02a",
		"target": "mediatek/filogic",
		"description": "OpenWrt 24.10.0 r28427-6df0e3d02a",
		"builddate": "1738624177"
	}
}

root@Kindness:~# cat /etc/config/network

config interface 'loopback'
	option device 'lo'
	option proto 'static'
	option ipaddr '127.0.0.1'
	option netmask '255.0.0.0'

config globals 'globals'
	option ula_prefix 'fd55:4a9b:b532::/48'
	option packet_steering '1'

config device
	option name 'br-lan'
	option type 'bridge'
	list ports 'lan1'
	list ports 'lan2'
	list ports 'lan3'
	list ports 'lan4'

config interface 'lan'
	option device 'br-lan'
	option proto 'static'
	option ipaddr '192.168.1.1'
	option netmask '255.255.255.0'
	option ip6assign '60'
	list dns '9.9.9.9'

config interface 'wan'
	option device 'wan'
	option proto 'dhcp'
	option peerdns '0'
	list dns '9.9.9.9'

config interface 'wan6'
	option device 'wan'
	option proto 'dhcpv6'

root@Kindness:~# cat /etc/config/wireless

config wifi-device 'radio0'
	option type 'mac80211'
	option path 'platform/soc/18000000.wifi'
	option band '2g'
	option channel '1'
	option htmode 'HE20'
	option country 'US'
	option cell_density '0'

config wifi-iface 'default_radio0'
	option device 'radio0'
	option network 'lan'
	option mode 'ap'
	option ssid 'Kindness'
	option encryption 'sae'
	option key ‘XXXXXXXXXX’
	option ocv '0'

config wifi-device 'radio1'
	option type 'mac80211'
	option path 'platform/soc/18000000.wifi+1'
	option band '5g'
	option channel '36'
	option htmode 'HE80'
	option country 'US'
	option cell_density '0'

config wifi-iface 'default_radio1'
	option device 'radio1'
	option network 'lan'
	option mode 'ap'
	option ssid 'Kindness'
	option encryption 'sae'
	option key ‘XXXXXXXXXX’
	option ocv '0'

root@Kindness:~# cat /etc/config/dhcp

config dnsmasq
	option domainneeded '1'
	option boguspriv '1'
	option filterwin2k '0'
	option localise_queries '1'
	option rebind_protection '1'
	option rebind_localhost '1'
	option local '/lan/'
	option domain 'lan'
	option expandhosts '1'
	option nonegcache '0'
	option cachesize '1000'
	option authoritative '1'
	option readethers '1'
	option leasefile '/tmp/dhcp.leases'
	option resolvfile '/tmp/resolv.conf.d/resolv.conf.auto'
	option nonwildcard '1'
	option localservice '1'
	option ednspacket_max '1232'
	option filter_aaaa '0'
	option filter_a '0'

config dhcp 'lan'
	option interface 'lan'
	option start '100'
	option limit '150'
	option leasetime '12h'
	option dhcpv4 'server'
	option dhcpv6 'server'
	option ra 'server'
	list ra_flags 'managed-config'
	list ra_flags 'other-config'

config dhcp 'wan'
	option interface 'wan'
	option ignore '1'

config odhcpd 'odhcpd'
	option maindhcp '0'
	option leasefile '/tmp/hosts/odhcpd'
	option leasetrigger '/usr/sbin/odhcpd-update'
	option loglevel '4'

root@Kindness:~# cat /etc/config/firewall
config defaults
	option syn_flood	1
	option input		REJECT
	option output		ACCEPT
	option forward		REJECT
# Uncomment this line to disable ipv6 rules
#	option disable_ipv6	1

config zone
	option name		lan
	list   network		'lan'
	option input		ACCEPT
	option output		ACCEPT
	option forward		ACCEPT

config zone
	option name		wan
	list   network		'wan'
	list   network		'wan6'
	option input		REJECT
	option output		ACCEPT
	option forward		REJECT
	option masq		1
	option mtu_fix		1

config forwarding
	option src		lan
	option dest		wan

# We need to accept udp packets on port 68,
# see https://dev.openwrt.org/ticket/4108
config rule
	option name		Allow-DHCP-Renew
	option src		wan
	option proto		udp
	option dest_port	68
	option target		ACCEPT
	option family		ipv4

# Allow IPv4 ping
config rule
	option name		Allow-Ping
	option src		wan
	option proto		icmp
	option icmp_type	echo-request
	option family		ipv4
	option target		ACCEPT

config rule
	option name		Allow-IGMP
	option src		wan
	option proto		igmp
	option family		ipv4
	option target		ACCEPT

# Allow DHCPv6 replies
# see https://github.com/openwrt/openwrt/issues/5066
config rule
	option name		Allow-DHCPv6
	option src		wan
	option proto		udp
	option dest_port	546
	option family		ipv6
	option target		ACCEPT

config rule
	option name		Allow-MLD
	option src		wan
	option proto		icmp
	option src_ip		fe80::/10
	list icmp_type		'130/0'
	list icmp_type		'131/0'
	list icmp_type		'132/0'
	list icmp_type		'143/0'
	option family		ipv6
	option target		ACCEPT

# Allow essential incoming IPv6 ICMP traffic
config rule
	option name		Allow-ICMPv6-Input
	option src		wan
	option proto	icmp
	list icmp_type		echo-request
	list icmp_type		echo-reply
	list icmp_type		destination-unreachable
	list icmp_type		packet-too-big
	list icmp_type		time-exceeded
	list icmp_type		bad-header
	list icmp_type		unknown-header-type
	list icmp_type		router-solicitation
	list icmp_type		neighbour-solicitation
	list icmp_type		router-advertisement
	list icmp_type		neighbour-advertisement
	option limit		1000/sec
	option family		ipv6
	option target		ACCEPT

# Allow essential forwarded IPv6 ICMP traffic
config rule
	option name		Allow-ICMPv6-Forward
	option src		wan
	option dest		*
	option proto		icmp
	list icmp_type		echo-request
	list icmp_type		echo-reply
	list icmp_type		destination-unreachable
	list icmp_type		packet-too-big
	list icmp_type		time-exceeded
	list icmp_type		bad-header
	list icmp_type		unknown-header-type
	option limit		1000/sec
	option family		ipv6
	option target		ACCEPT

config rule
	option name		Allow-IPSec-ESP
	option src		wan
	option dest		lan
	option proto		esp
	option target		ACCEPT

config rule
	option name		Allow-ISAKMP
	option src		wan
	option dest		lan
	option dest_port	500
	option proto		udp
	option target		ACCEPT


### EXAMPLE CONFIG SECTIONS
# do not allow a specific ip to access wan
#config rule
#	option src		lan
#	option src_ip	XXXXXXXXXX
#	option dest		wan
#	option proto	tcp
#	option target	REJECT

# block a specific mac on wan
#config rule
#	option dest		wan
#	option src_mac	XXXXXXXXXX
#	option target	REJECT

# block incoming ICMP traffic on a zone
#config rule
#	option src		lan
#	option proto	ICMP
#	option target	DROP

# port redirect port coming in on wan to lan
#config redirect
#	option src			wan
#	option src_dport	80
#	option dest			lan
#	option dest_ip		XXXXXXXXXX
#	option dest_port	80
#	option proto		tcp

# port redirect of remapped ssh port (22001) on wan
#config redirect
#	option src		wan
#	option src_dport	22001
#	option dest		lan
#	option dest_port	22
#	option proto		tcp

### FULL CONFIG SECTIONS
#config rule
#	option src		lan
#	option src_ip	XXXXXXXXXX
#	option src_mac	XXXXXXXXXX
#	option src_port	80
#	option dest		wan
#	option dest_ip	XXXXXXXXXX
#	option dest_port	120
#	option proto	tcp
#	option target	REJECT

#config redirect
#	option src		lan
#	option src_ip	XXXXXXXXXX
#	option src_mac	XXXXXXXXXX
#	option src_port		1024
#	option src_dport	80
#	option dest_ip	XXXXXXXXXX
#	option dest_port	120
#	option proto	tcp
2

As you can probably guess, this is a problem related to your computer and the VPN configuration, not OpenWrt.

This could be explained by how DNS is handled by the browsers... some of them will use hard-coded (or at least "preferred") DNS servers and/or DoH/DoT. Again, it's not related to OpenWrt.

When the VPN is active on your computer, it will tunnel all traffic, including the DNS requests through to the VPN provider's endpoint. That means that your computer won't be able to get DNS responses from the DNS server running on the OpenWrt router.

Your configuration looks fine. There are no issues here.

Reach out to your VPN provider for assistance since this is an issue with the local configuration of your computer (DNS settings and/or VPN configuration itself) and/or their service.

2 Likes
3

Peter, many thanks for responding even though this is not an OpenWrt issue (I didn't know). And thanks for looking through my configuration. I was hoping that you would respond because you are always helpful.

4

Glad I could help in general even though we cannot completely resolve your issue since it isn’t an openwrt related problem.

That said:

If your problem is solved, please consider marking this topic as [Solved]. See How to mark a topic as [Solved] for a short how-to.
Thanks! :slight_smile:

5

Re-starting my computer fixed the problem. I wish that I knew why.

6

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