Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 
Step-by-Step Configuration and Troubleshooting Best Practices for the NGFW, NGIPS and AMP Technologies A Visual Guide to the Cisco Firepower Threat Defense (FTD)
New Member

Problem with NAT.

I have a problem in a router c2811.

This router has an Isdn access to a central site using a Bri interface (wic-1b-s/t-v3).

The router has the following IOS: c2800nm-spservicesk9-mz.123-8.T8.bin.

This same router has an Internet access using an Adsl interface and at same time has an Isdn access to a customer, a client. Behind this router I have a firewall, an ASA5520.

The configuration can be seen in one file attached to this.

The problem is like this,

In the ASA, the traffic that goes to the outside is nated with the ip address of the outside interface.

In the router, the traffic that goes to the internet are not nated, but the traffic to the customer has to be nated (the client asked to be like this) with the ip address of the Isdn connection.

If I make a connection test (a “ping”) to the client internal network, from the ASA. I have no success. But if I do the same test in the router (with source in the internal interface of the router) I have success.

What I can see is that the packets are coming from the ASA and are going to the router internal interface. In the router they are nated and then are sent to the bri interface.

They are then sanded to the client internal network.

The replay to the “ping” is then sanded to my router (c2811), and I can still see this coming to my Bri interface.

The traffic, I mean, the destination ip address of the traffic is then translated to the ip address of the outside interface of the ASA…

This last thing should be happening, but it's not.

Almost the times I don't succeed in “pinging” the internal network of the client.

What I have in the ASA is:

ping outside repeat 15

Type escape sequence to abort.

Sending 15, 100-byte ICMP Echos to, timeout is 2 seconds:


Success rate is 6 percent (1/15), round-trip min/avg/max = 310/310/310 ms

In the router I have this:

*Feb 3 22:58:13.044: %SEC-6-IPACCESSLOGDP: list 113 permitted icmp -> (0/0), 12 packets

*Feb 3 22:58:13.044: %SEC-6-IPACCESSLOGDP: list 114 permitted icmp -> (8/0), 15 packets

*Feb 3 22:58:13.044: %SEC-6-IPACCESSLOGDP: list 115 permitted icmp -> (0/0), 1 packet

In the ASA I have this routing:

route outside 1

route outside 1

Can some one help me?

I can not antherstand what is appening.

Thanks in advance,


New Member

Re: Problem with NAT.

A few comments...

I see on the router that you're doing NAT from the Fast0/0 to the Dialer0 for the traffic that goes

to the customer side (

The NAT ACL must be a permit IP (not recommended to use ICMP)

I have had problems with NAT when I use the work ''any'' in the ACL. Trying replacing ''any''

with the source network address where the traffic is coming from...

For example instead of having this:

access-list 112 permit icmp any

access-list 112 permit icmp any host

access-list 112 permit ip any

access-list 112 permit ip any host

access-list 112 deny ip any any

Try the following:

access-list 112 permit ip

Let me know if it works...

CreatePlease to create content