問題：服務器IP改變以後，android dns cache 由於沒有被清除，導致域名解析出錯。
http://stackoverflow.com/questions/2101762/android-flush-dns
同時 android dns cache 緩存清除沒有提供上層接口，但是android 系統層卻提供了這種功能，因此需要導出api 給上層程序使用。
查看ndc interface list
| interface | list |
| readrxcounter| readtxcounter | |
| getthrottle<iface><”rx|tx”> | |
| setthrottle<iface><rx_kbps|tx_kbps> | |
| driver<iface><cmd><args> | |
| route<add|remove> <iface> <”default|secondary”><dst> <prefix> <gateway> | |
| list_ttys | |
| ipfwd | status |
| enable|disable | |
| tether | status |
| start-reverse|stop-reverse | |
| stop< | |
| start<addr_1 addr_2 addr_3 addr_4 [addr_2n]> | |
| interface<add|remove|list> | |
| dnslist | |
| dnsset <addr_1> < addr_2> | |
| nat | <enable|disable><iface><extface><addrcnt><nated-ipaddr/prelength> |
| pppd | attach<tty> <addr_local> <add_remote> <dns_1><dns_2> |
| detach<tty> | |
| softap | startap|stopap |
| fwreload<iface> <AP|P2P> | |
| clients | |
| status | |
| set<iface> <SSID> <wpa-psk|wpa2-psk|open> [<key><channel> <preamble><max SCB>] | |
| resolver | setdefaultif<iface> |
| setifdns<iface><dns_1><dns_2> | |
| flushdefaultif | |
| flushif<iface> | |
| bandwith | enable|disable |
| removequota|rq | |
| getquota|gq | |
| getiquota|giq<iface> | |
| setquota|sq<bytes> <iface> | |
| removequota|rqs<iface> | |
| removeiiquota|riq<iface> | |
| setiquota|sq<interface><bytes> | |
| addnaughtyapps|ana<appUid> | |
| removenaughtyapps|rna<appUid> | |
| setgolbalalert|sga<bytes> | |
| debugsettetherglobalalert|dstga<iface0><iface1> | |
| setsharedalert|ssa<bytes> | |
| removesharedalert|rsa | |
| setinterfacealert|sia<iface><bytes> | |
| removeinterfacealert|ria<iface> | |
| gettetherstats|gts<iface0><iface1> | |
| idletimer | enable|disable |
| add|remove<iface><timeout><classLabel> | |
| firewall | enable|disable|is_enabled |
| set_interface_rule<rmnet0><allow|deny> | |
| set_egress_source_rule<ip_addr><allow|deny> | |
| set_egress_dest_rule<ip_addr><port><allow|deny> | |
| set_uid_rule<uid><allow|deny> | |
| clatd |
stop|status|start<iface> |
在實際代碼調試時，可用flushdefaultif 命令清除DNS，實際代碼中可以通過分析flushdefualtif命令流程，新增api接口供上層使用。