2 routers Alcatel Speedtouch

[Mel]

Hi all routing experts out there,

I thought I have a simple task to achieve, I'd like to explain my router
to route everything from port DIALUP_PPP1 to eth0 and back again.
In this way I can use my Cisco router and just use the Alcatel to do
the ADSL modem stuff. But till now I was not able to comnfigure the
Alcatl correctly.
(Alcatel Speedtouch 610)

The Alcatel works properly if I directly attach it to My PC
and assign the public IP to My PC. So here is no hardware
problem, it just depends on the Alcatel configuration.

To test my Cisco router I directly attached it to a PC on both
sides. I verified that the Cisco does the NATTING correctly.

-------- -----------------
Test PC ------| Cisco Router |----- My PC
| Port |
| eth1 eth0 |
| |
| NAT to the |
| public IP |
| 213.33.120.10 |
-----------------

IP Adresses:
------------
|Cisco Router |
Test PC |eth1 eth1| My PC
10.10.10.253 -- |10.10.10.254 10.227.110.254| -- 10.227.110.5

When I ping from My PC 10.227.110.5 to the Test PC 10.10.10.253 then my
Cisco takes the IP packet, applies the natting and forwards the packet
to the next router, in this case to the Test PC.
The Test PC gets the Ping ICMP packet with a source IP of 213.33.120.10 and
the destination IP 10.10.10.253.
The Test PC answers the ping, the CISCO router maps the natted address back
and My PC gets the ping answer.
So everything works great in this way.

Now I disconnect my Test PC and connect my Alcatel ADSL modem/router.

-------------- ---------------------- -----------------
Provider net | ----| My Alcatel |------| Cisco Router |----- My PC
| | Port | | Port |
-------------- | DIALUP_PPP1 eth0| | eth1 eth0 |
---------------------- | |
| NAT to the |
| public IP |
| 213.33.120.10 |
-----------------

IP Adresses:
------------
Alcatel | |Cisco Router |
DIALUP_PPP1 eth0| |eth1 eth1| My PC
10.10.10.253| -- |10.10.10.254 10.227.110.254| -- 10.227.110.5

When I ping from My PC 10.227.110.5 to the Test PC 10.10.10.253 then the
Alcatel does not return the ping.
Why does my Alcatel not answer the ping?
I understand that a firewall that blocks ICMP could cause this,
therefore I ensured to deactivate the firewall.
Is there a difference in attaching a PC withe IP 10.10.10.253 to the
CISCO and to attach an Alcatel router with the IP 10.10.10.253 to the CISCO?

Is the Routing table necessary to answer the ping?

Is there anything else left to consider?

Thanks for any help.
-Mel