Now I access to Internet through ADSL router. At the same time I want to run some service on my ubuntu, so I need a static LAN IP such as 192.168.1.100.

I use network-manager to config my network. But the problem is that if I click DSL to access the Internet. My eth0's static ip setting will be change. So I have to manually change it back to 192.168.1.100 by using ifconfig.

My problem is that is there any method that I can get the DSL and LAN static IP work together without typing ifconfig cmd every time?

Yes, configure your DSL modem/router to use a static IP and not use DHCP.

Thanks for your reply.
But I don't think this is the problem. I already shut down the dhcp service of my router.
My situation is like this, I use network-manager to manage my network.
In the "Network Connection" I have Wired and DSL.
In Wired tab, I set up the LAN with static IP. say 192.168.1.100
In DSL tab, I set up my pppoe name and password.
But the problem is that :

If I use LAN, then I got
eth0 Link encap:Ethernet HWaddr 1c:6f:65:4e:d2:56
inet addr:192.168.1.100 Bcast:192.168.1.255 Mask:255.255.255.0
inet6 addr: fe80::1e6f:65ff:fe4e:d256/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:73580 errors:0 dropped:0 overruns:0 frame:0
TX packets:67896 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:72792067 (72.7 MB) TX bytes:12291637 (12.2 MB)
Interrupt:33 Base address:0x2000

If I use DSL to access to the Internet, then
eth0 Link encap:Ethernet HWaddr 1c:6f:65:4e:d2:56
inet6 addr: fe80::1e6f:65ff:fe4e:d256/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:73971 errors:0 dropped:0 overruns:0 frame:0
TX packets:68394 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:73113338 (73.1 MB) TX bytes:12355522 (12.3 MB)
Interrupt:33 Base address:0x2000

ppp0 Link encap:Point-to-Point Protocol
inet addr: (my IP here) P-t-P: (some IP here) Mask:255.255.255.255
UP POINTOPOINT RUNNING NOARP MULTICAST MTU:1492 Metric:1
RX packets:353 errors:0 dropped:0 overruns:0 frame:0
TX packets:364 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:3
RX bytes:309982 (309.9 KB) TX bytes:44478 (44.4 KB)

Please notice that the static IP of eth0 has been changed. If I use LAN again, eth0 will get 192.168.1.100, but the ppp0 connection is gone!
I can only use ifconfig eth0 192.168.1.100 to config it again without broken the ppp0 connection.
My question is, Can I get these two network working together without typing the ifconfig cmd everytime?