How to access the Internet through a specific adapter?

Question

linux

There is a router on the padavan firmware that goes through a pptp tunnel. But the users who use it go through a regular ip (Not a vpn). How to make it go out through the ppp5 adapter

Ifconfig
br0       Link encap:Ethernet  HWaddr 50:64:2B:77:xx:xx
          inet addr:192.168.1.1  Bcast:192.168.1.255  Mask:255.255.255.0
          inet6 addr: fe80::5264:2bff:xxxx:xxxx/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:122056 errors:0 dropped:0 overruns:0 frame:0
          TX packets:54834 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:30266024 (28.8 MiB)  TX bytes:26406550 (25.1 MiB)

eth2      Link encap:Ethernet  HWaddr 50:64:2B:77:xx:xx
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:122662 errors:0 dropped:0 overruns:0 frame:0
          TX packets:55985 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:32531572 (31.0 MiB)  TX bytes:26852861 (25.6 MiB)
          Interrupt:5

eth2.1    Link encap:Ethernet  HWaddr 50:64:2B:77:xx:xx
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:120846 errors:0 dropped:5 overruns:0 frame:0
          TX packets:54783 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:29933048 (28.5 MiB)  TX bytes:26241617 (25.0 MiB)

eth2.2    Link encap:Ethernet  HWaddr 50:64:2B:77:xx:xx
          inet6 addr: fe80::5264:xxxx:xxxx:499b/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:12 errors:0 dropped:0 overruns:0 frame:0
          TX packets:12 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:998 (998.0 B)  TX bytes:998 (998.0 B)

ppp5      Link encap:Point-to-Point Protocol
          inet addr:10.8.0.2  P-t-P:10.8.0.1  Mask:255.255.255.255
          UP POINTOPOINT RUNNING NOARP MULTICAST  MTU:1400  Metric:1
          RX packets:218 errors:0 dropped:0 overruns:0 frame:0
          TX packets:7 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:3
          RX bytes:12296 (12.0 KiB)  TX bytes:106 (106.0 B)

ra0       Link encap:Ethernet  HWaddr 50:64:2B:77:xx:xx
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:2091 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1186 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:414854 (405.1 KiB)  TX bytes:385952 (376.9 KiB)
          Interrupt:6

rai0      Link encap:Ethernet  HWaddr 50:64:2B:77:xx:xx
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)
          Interrupt:4

weth0     Link encap:Ethernet  HWaddr 1C:49:7B:31:xx:xx
          inet addr:192.168.0.17  Bcast:192.168.0.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:40788 errors:0 dropped:0 overruns:0 frame:0
          TX packets:108363 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:13739355 (13.1 MiB)  TX bytes:30118819 (28.7 MiB)

Answer 1

configure routing so that default gw is behind the desired adapter, configure masquerading so that it comes from the desired address.