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先在配置文件内禁用ipv6 dhcp服务：

/etc/config/dhcp 
config dhcp 'lan'
        option interface 'lan'
        option start '150'
        option limit '100'
        option leasetime '12h'
        option ra 'disabled'
        option dhcpv6 'disabled'

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

关闭odhcpd:

/etc/init.d/odhcpd stop
/etc/init.d/odhcpd disable

修改dnsmasq配置文件开启ra服务：

/etc/dnsmasq.conf 
enable-ra
dhcp-range=::,constructor:br-lan,ra-only
#其它slaac ra-stateless等参考man文档

只想通过ipv4查询dns，下面patch让dnsmasq无状态分配ip时候不包含RDNSS，这样客户端只配置ipv4 dns而不配置ipv6 dns。

diff -urN dnsmasq-2.86/src/radv.c dnsmasq-2.86-bak/src/radv.c
--- dnsmasq-2.86/src/radv.c     2021-09-09 04:21:22.000000000 +0800
+++ dnsmasq-2.86-bak/src/radv.c 2022-01-23 11:57:01.818963642 +0800
@@ -507,7 +507,7 @@
        }
     }
 
-  if (daemon->port == NAMESERVER_PORT && !done_dns && parm.link_pref_time != 0)
+  if ( 0 && daemon->port == NAMESERVER_PORT && !done_dns && parm.link_pref_time != 0)
     {
       /* default == us, as long as we are supplying DNS service. */
       put_opt6_char(ICMP6_OPT_RDNSS);

odhcpd新版本参数dns_service也可实现此需求，不使用dhcpv6可尝试使用ra_dns参数关闭ra dns？
再次开启ipv6 dns服务，如果有配置dhcp6 dns服务器，dnsmasq会将其设置为RDNSS:

dhcp-option=option6:dns-server,[xxxx:xxxx:xxxx:xxxx::1]