DNS over openvpn

Hi everyone
I use router as openvpn client
already upload my openvpn config and it’s work
but only DNS have some problem, can not use DNS provide by VPN server

I Disable peer DNS and configure by
uci set network.wan.peerdns="0"
uci set network.wan6.peerdns="0"

/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 authoritative '1'
        option readethers '1'
        option leasefile '/tmp/dhcp.leases'
        option nonwildcard '1'
        option localservice '1'
        option resolvfile '/tmp/resolv.conf.vpn'

config dhcp 'lan'
        option interface 'lan'
        option start '100'
        option limit '150'
        option leasetime '12h'
        option force '1'
        option dhcpv6 'server'
        option ra 'server'

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'

config domain 'localhost'
        option name 'console.gl-inet.com'
        option ip '192.168.8.1'

resolv.conf.vpn
nameserver 10.21.1.25

resolv.conf.auto
nameserver 192.168.7.1

when i disconnect openvpn resolv.conf.auto it’s work fine
why switch to resolv.conf.vpn is broke, i don’t have any idea

can somebody help me ?
thanks

Where is the name server??

resolv.conf.vpn
nameserver 10.21.1.25

resolv.conf.auto
nameserver 192.168.7.1