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New Member

Dynamic PAT with DHCP assignet address support

Hello all

I have the following configuration but I'm not shure is this really supported on the IOS 12.3(24)I running on.

ISP/Internet--Cable Modem--Router--LAN


ISP provide dynamic assignet ip address by DHCP to the router outside interface fa0/0. Inside is a private ip range ( on fa0/1 configured. Inside private address use dynamic PAT to reach the internet via the interface fa0/0 (outside).

With this configuration I can access the internet with the web browser but I can not ping or do any vpn access to a global internet address.

When I configure a satic address to the interface fa0/0 it works but just for one address.

here the relevant configuration of the router

interface FastEthernet0/0

description Pulic Network

ip address dhcp

ip nat outside


interface FastEthernet0/1

description Privat Network

ip address

ip nat inside

ip nat inside source route-map nat interface FastEthernet0/0 overload

*** Static NAT configuration ***

(ip nat inside source static interface fa0/0)

access-list 101 permit ip

route-map nat permit 10

match ip address 101

ip route FastEthernet0/0

Thanks for any replay

New Member

Re: Dynamic PAT with DHCP assignet address support

Here's the config that I use on my 1751 router. I am running 12.4 have the exact same sceanrio as you... cable modem (DHCP IP)-router-lan. See if this works for you as well. I also have a few NAT entries that I use to get back inside as well. The IP routes that point to NULL0 are known subnets that are typically spoofed (I believe).


New Member

Re: Dynamic PAT with DHCP assignet address support

Hello Rick

thank you for the replay. It seems this is not supported on the IOS 12.3 version. My configuration looks simalar as yours. I attached my configuration with changed passwords and ip addresses. A ping from a inside host to the outside is only working when I configure:

ip nat inside source static interface fastethernet 0/0,

but i can just configure one static nat entry. As soon I configure a secondary static configuration for a inside host the first static configuration is overwriten. IOS 12.4 is not supported on my Cisco2621 router, so the last version I can use is 12.3.


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