DDN专线和ADSL的双线互备问题

shaying110

我的配置是：
DDN－－ROUTER2651XM（F0/0）ip nat outside
ADSL－－ROUTER2651XM(ADSL 口)  ip nat outside
lan－－ROUTER2651XM(F0/1)  ip nat inside


hostname R2651
!
boot-start-marker
boot-end-marker
!
enable secret 5 $1$7KQ4ewww.2342q
enable password 7 05080qerq5713eD001A
!
username china password 7 3432020B0033214321C0813171B0D163E65
no network-clock-participate slot 1
no network-clock-participate wic 0
vpdn enable
!
vpdn-group pppoe
request-dialin
  protocol pppoe
!
no aaa new-model
ip subnet-zero
ip ssh authentication-retries 5
!
!
ip cef
no ip domain lookup
ip domain name CHINAABC.com
!
interface FastEthernet0/0
ip address 172.16.16.42 255.255.255.252
ip nat outside
ip virtual-reassembly
duplex auto
speed auto
!
interface Serial0/0
no ip address
shutdown
no fair-queue
interface ATM0/1
no ip address
no atm ilmi-keepalive
dsl operating-mode auto
hold-queue 224 in
pvc 0/35
  encapsulation aal5snap
  pppoe-client dial-pool-number 1
!
!
interface FastEthernet0/1
ip address 192.168.4.1 255.255.255.0 secondary
ip address 192.168.3.254 255.255.255.128 secondary
ip address X.X.X.X 255.255.255.240
ip nat inside
ip virtual-reassembly
ip tcp adjust-mss 1452
duplex auto
speed auto
!
interface Dialer1
mtu 1483
ip address negotiated
ip nat outside
ip virtual-reassembly
encapsulation ppp
dialer pool 1
ppp chap hostname username
ppp chap password 7 passwd
ppp pap sent-username username password 7 passwd
!
!
ip classless
ip route 0.0.0.0 0.0.0.0 172.16.16.41
ip route 0.0.0.0 0.0.0.0 Dialer1 150
!
no ip http server
no ip http secure-server
!
ip nat pool china x.x.x.x  x.x.x.x netmask netmask

ip nat inside source list 101 pool china overload
access-list 101 permit ip 192.168.3.128 0.0.0.127 any


这样是正常的DDN连接，当我再加一条ADSL的时候　
用ip nat inside source list 101 interface Dialer1 overload时
就有%Dynamic mapping in use, cannot change报错
当no ip nat inside source list 101 pool china overload　再
ip nat inside source list 101 interface Dialer1 overload时就正常了
反之也一样这样的话就不能实行了ADSL和DDN的热备了，甚至当一条线DOWN时
也得人工在ROUTER上做一条命令才行的啊

哪位大侠给帮帮忙，想个办法：
最好是两条线的热备



要不冷备也行，不要当一条线DOWN时，人工在ROUTER上做上一条ip nat inside source ****

也好啊