Android网络设置（route & DNS）

route设置

android4.4只使用了一份路由表，使用busybox route就可以完成路由表的设置，从android5.0之后，考虑要对多网络的支持，采用了多路由表，下面的设置方法只适用于android4.4之前的版本，android5.0之后的版本路由表如何设置留到以后再说明。

1、查看路由表 busybox route -n

Kernel IP routing table

Destination Gateway Genmask Flags Metric Ref Use Iface

0.0.0.0 192.168.7.1 0.0.0.0 UG 0 0 0 eth0

0.0.0.0 192.168.7.1 0.0.0.0 UG 202 0 0 eth0

192.168.0.0 0.0.0.0 255.255.248.0 U 0 0 0 eth0

192.168.0.0 0.0.0.0 255.255.248.0 U 202 0 0 eth0

192.168.7.1 0.0.0.0 255.255.255.255 UH 0 0 0 eth0

2、删除默认路由 busybox route del default

Kernel IP routing table

Destination Gateway Genmask Flags Metric Ref Use Iface

0.0.0.0 192.168.7.1 0.0.0.0 UG 202 0 0 eth0

192.168.0.0 0.0.0.0 255.255.248.0 U 0 0 0 eth0

192.168.0.0 0.0.0.0 255.255.248.0 U 202 0 0 eth0

192.168.7.1 0.0.0.0 255.255.255.255 UH 0 0 0 eth0

3、添加一条默认路由 busybox route add -net 0.0.0.0 gw 192.168.7.1 netmask 0.0.0.0 dev eth0

Kernel IP routing table

Destination Gateway Genmask Flags Metric Ref Use Iface

0.0.0.0 192.168.7.1 0.0.0.0 UG 0 0 0 eth0

192.168.0.0 0.0.0.0 255.255.248.0 U 0 0 0 eth0

192.168.0.0 0.0.0.0 255.255.248.0 U 202 0 0 eth0

192.168.7.1 0.0.0.0 255.255.255.255 UH 0 0 0 eth0

4、删除一条主机路由 busybox route del -host 192.168.7.1 dev eth0

Kernel IP routing table

Destination Gateway Genmask Flags Metric Ref Use Iface

0.0.0.0 192.168.7.1 0.0.0.0 UG 0 0 0 eth0

192.168.0.0 0.0.0.0 255.255.248.0 U 0 0 0 eth0

192.168.0.0 0.0.0.0 255.255.248.0 U 202 0 0 eth0

5、添加一条主机路由 busybox route add -host 192.168.7.1 dev eth0

Kernel IP routing table

Destination Gateway Genmask Flags Metric Ref Use Iface

0.0.0.0 192.168.7.1 0.0.0.0 UG 0 0 0 eth0

192.168.0.0 0.0.0.0 255.255.248.0 U 0 0 0 eth0

192.168.0.0 0.0.0.0 255.255.248.0 U 202 0 0 eth0

192.168.7.1 0.0.0.0 255.255.255.255 UH 0 0 0 eth0

6、删除一条网络路由 busybox route del -net 192.168.0.0 netmask 255.255.248.0 dev eth

Kernel IP routing table

Destination Gateway Genmask Flags Metric Ref Use Iface

0.0.0.0 192.168.7.1 0.0.0.0 UG 0 0 0 eth0

192.168.0.0 0.0.0.0 255.255.248.0 U 202 0 0 eth0

7、添加一条网络路由 busybox route add -net 192.168.0.0 netmask 255.255.248.0 dev eth

Kernel IP routing table

Destination Gateway Genmask Flags Metric Ref Use Iface

0.0.0.0 192.168.7.1 0.0.0.0 UG 0 0 0 eth0

192.168.0.0 0.0.0.0 255.255.248.0 U 0 0 0 eth0

192.168.0.0 0.0.0.0 255.255.248.0 U 202 0 0 eth0

DNS Server设置

同样以android4.4为例来进行说明，android系统中，不管是dns server的设置，还是域名解析，都是由netd进程来执行的，netd与dns的相关操作是调用了一个netbsd的库，netd中dns server设置对应于文件ResolverController.cpp，域名解析对应于文件DnsProxyListener.cpp。

原生的android系统只提供了设置系统dns server的接口，而没有提供查看系统dns server的接口，需要自己添加代码来实现。

通过ndc配合netd可以对android dns进行设置和查看。

1、设置dns interface & server

ndc resolver setdefaultif eth0

ndc resolver setifdns eth0 “” 192.168.7.2

2、查看dns interface

ndc resolver getdefaultif

226 0 DNS default interface is eth0

3、查看dns server

ndc resolver getdefaultServer 1

226 0 DNS default server[1] is 192.168.7.2

其中2、3是通过添加如下代码后才能支持；

1) system\netd\CommandListener.cpp

if (!strcmp(argv[1], "getdefaultif")) { // "resolver getdefaultif"
char ifname[IF_NAMESIZE] = {0};
sResolverCtrl->getDefaultInterface(ifname, sizeof(ifname));
char *msg = NULL;
asprintf(&msg, "DNS default interface is %s", ifname);
cli->sendMsg(ResponseCode::DnsInfoResult, msg, false);
free(msg);
} else if (!strcmp(argv[1], "getdefaultServer")) { // "resolver getdefaultServer num"
if (argc == 3) {
char addr[128] = {0};
sResolverCtrl->getDefaultDnsServers(addr, sizeof(addr), atoi(argv[2]));
char *msg = NULL;
asprintf(&msg, "DNS default server[%d] is %s", atoi(argv[2]), addr);
cli->sendMsg(ResponseCode::DnsInfoResult, msg, false);
free(msg);
} else {
cli->sendMsg(ResponseCode::CommandSyntaxError,
"Wrong number of arguments to resolver getdefaultServer", false);
return 0;
}
}

2) system\netd\ResolverController.cpp

void ResolverController::getDefaultInterface(char* iface, int len) {
_resolv_get_default_iface(iface, len);
}
void ResolverController::getDefaultDnsServers(char* addr, int addrLen, int num) {
_resolv_cache_get_nameserver(num, addr, addrLen);
}

3) _resolv_get_default_iface 和 _resolv_cache_get_nameserver是netbsd的函数，这两个并不对外开放，netd要调用这两个函数，需要修改加上如下的patch；

diff

--- a/libc/private/resolv_cache.h

+++ b/libc/private/resolv_cache.h

@@ -34,6 +34,8 @@

struct __res_state;

struct resolv_cache;  /* for
4000
ward */

+__BEGIN_DECLS

+

/* gets the cache for an interface. Set ifname argument to NULL or

* empty buffer ('\0') to get cache for default interface.

* returned cache might be NULL*/

@@ -48,7 +50,6 @@ extern void  _resolv_cache_reset( unsigned  generation );

/* Gets the address of the n:th name server for the default interface

* Return length of address on success else 0.

* Note: The first name server is at n = 1 */

-__LIBC_HIDDEN__

extern int _resolv_cache_get_nameserver(int n, char* addr, int addrLen);

/* Gets the address of the n:th name server for a certain interface

@@ -81,7 +82,6 @@ extern struct in_addr* _resolv_get_addr_of_iface(const char* ifname);

/* Copy the name of the default interface to the provided buffer.

* Returns the string length of the default interface,

* be that less or more than the buffLen, or 0 if nothing had been written */

-__LIBC_HIDDEN__

extern size_t _resolv_get_default_iface(char* buff, size_t buffLen);

/* sets the name server addresses to the provided res_state structure. The

@@ -124,4 +124,6 @@ _resolv_cache_query_failed( struct resolv_cache* cache,

const void* query,

int         querylen);

+__END_DECLS

+

#endif /* _RESOLV_CACHE_H_ */