今天意外发现使用自建立的DNS出现解析异常。
在服务器上查看日志，出现了大量了IPv6解析报错:
Jan 16 14:08:45 DNS named[8855]: network unreachable resolving 'dns1.ourglb0.org/A/IN': 2001:500:e::1#53 Jan 16 14:08:45 DNS named[8855]: network unreachable resolving 'dns3.ourglb0.org/A/IN': 2001:500:e::1#53 Jan 16 14:08:45 DNS named[8855]: network unreachable resolving 'dns4.ourglb0.info/A/IN': 2001:500:1b::1#53 Jan 16 14:08:45 DNS named[8855]: network unreachable resolving 'dns1.ourglb0.org/AAAA/IN': 2001:500:e::1#53 Jan 16 14:08:45 DNS named[8855]: network unreachable resolving 'dns2.ourglb0.info/A/IN': 2001:500:1b::1#53 Jan 16 14:08:45 DNS named[8855]: network unreachable resolving 'dns4.ourglb0.info/AAAA/IN': 2001:500:1b::1#53 Jan 16 14:08:45 DNS named[8855]: network unreachable resolving 'dns3.ourglb0.org/AAAA/IN': 2001:500:e::1#53 Jan 16 14:08:45 DNS named[8855]: network unreachable resolving 'dns2.ourglb0.info/AAAA/IN': 2001:500:1b::1#53 Jan 16 14:08:45 DNS named[8855]: network unreachable resolving 'dns4.ourglb0.info/A/IN': 2001:500:49::1#53 Jan 16 14:08:45 DNS named[8855]: network unreachable resolving 'dns3.ourglb0.org/A/IN': 2001:500:40::1#53 Jan 16 14:08:45 DNS named[8855]: network unreachable resolving 'dns2.ourglb0.info/A/IN': 2001:500:49::1#53 Jan 16 14:08:45 DNS named[8855]: network unreachable resolving 'dns5.ourglb0.org/A/IN': 2001:500:e::1#53 Jan 16 14:08:45 DNS named[8855]: network unreachable resolving 'dns4.ourglb0.info/AAAA/IN': 2001:500:49::1#53 Jan 16 14:08:45 DNS named[8855]: network unreachable resolving 'dns3.ourglb0.org/AAAA/IN': 2001:500:40::1#53 Jan 16 14:08:46 DNS named[8855]: network unreachable resolving 'dns4.mwcloudcdn.info/A/IN': 2001:500:1b::1#53 Jan 16 14:08:46 DNS named[8855]: network unreachable resolving 'dns4.mwcloudcdn.info/A/IN': 2001:500:49::1#53
此为客户端请求了IPv6的域名解析，而DNS递归解析时获得了IPv6地址，而IPv6不可用，故报此错。
我将客户端（Windows 10）的IPv6协议禁用掉，然后再测试解析正常得到IPv4地址。
看样子的确是客户端请求了 IPv6 的AAAA记录导致的，但不可能在客户端上进行操作；于是经过查找，在bind启动进程上加上 -4 选项可以让bind仅提供IPv4的查询请求。
[root@DNS bind9]# ps -ef | grep named named 8855 1 0 13:59 ? 00:00:02 named -u named root 12337 977 0 15:38 pts/2 00:00:00 grep --color=auto named [root@DNS bind9]# kill 8855 [root@DNS bind9]# named -4 -u named [root@DNS bind9]# ps -ef | grep named named 12339 1 1 15:38 ? 00:00:00 named -4 -u named root 12358 977 0 15:38 pts/2 00:00:00 grep --color=auto named [root@DNS bind9]# netstat -nlput | grep name Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name tcp 0 0 172.16.220.224:53 0.0.0.0:* LISTEN 12339/named tcp 0 0 127.0.0.1:53 0.0.0.0:* LISTEN 12339/named tcp 0 0 127.0.0.1:953 0.0.0.0:* LISTEN 12339/named udp 0 0 192.168.122.1:53 0.0.0.0:* 12339/named udp 0 0 172.16.220.224:53 0.0.0.0:* 12339/named udp 0 0 127.0.0.1:53 0.0.0.0:* 12339/named [root@DNS bind9]#
这样bind就仅处理IPv4的域名请求。