Simple multihoming with route-map and NAT

I'm having tough time trying to set up something that looks like it
should be rather easy:

Cisco router with:
- one FastEthernet port connected to LAN
- one Ethernet port connected to DSL (PPPoE)
- one Serial port connected point-to-point

DSL gets it's IP assigned from ISP (dynamic), Serial port has static
public IP addresses.

What I'm trying to achieve is to route outgoing mail (SMTP) thru Serial
port. All other outgoing traffic should be sent thru DSL, also NAT-ed.

Can anyone provide some sample configuration or advice? What I tried to
do looks something like:

=====================================================
interface FastEthernet0
ip address _local_private_address_
ip nat inside

interface Serial0.1 point-to-point
ip address _public_static_address_
ip nat outside

interface Ethernet0
no ip address
pppoe enable

interface Dialer0
ip address negotiated
ip nat outside

access-list 102 remark allow NAT from local addresses
access-list 102 permit ip _local_network_ 0.0.0.255 any

ip access-list extended alNATtoSerial
permit tcp _local_network_ 0.0.0.255 any eq smtp

route-map rmNATtoDSL permit 10
match ip address 102

route-map rmNATtoSerial permit 10
match ip address alNATtoSerial

ip nat inside source route-map rmNATtoDSL interface Dialer0 overload
ip nat inside source route-map rmNATtoSerial interface Serial0.1
overload
=====================================================

Thanks in advance,
Bruno

 

Among other problems, the route maps are only applied when a translation
which is NOT in the translation table is required (at connection setup). If
the link then fails, the bad translation for the failed link will continue
in use until you stop using it and it times out. You get lucky and have the
translate cleared if the serial line goes down hard, but even if you unplug
the ethernet, the translations going through it will remain.

It can also be a challenge detecting when one of your links is down.

A search on ping based routing will get you most of the past messages where
this topic has been generally addressed.

Good luck and have fun!