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I have a pool of public IP addresses of 203.82.x.x/28 which is running with PAT/Overload with a private IP subnet of 172.22.x.x on a Cisco 2900 series router.

The radio modem Ethernet link connects to the router interface with a public IP address, and the LAN connects to another interface of the router with a private IP address; a simple configuration.

I know I can split the connection from the radio modem, and put it directly into my LAN switch, using the public network with my LAN hosts. It works fine.

I wonder, how do I bypass the NAT configuration so that I can just change LAN hosts IP addresses to public IP addresses and access the Internet directly, without splitting the connection from the radio modem?

Please correct me If I am thinking wrong.

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    Is the public IP of your router also in the 203.82.x.x/28 subnet? – Ron Trunk Aug 18 '15 at 16:06
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    Welcome to NE, we hope you will both contribute to and learn from this community. You could improve your question by editing it to add more details. You may find our Question Checklist helpful when editing your question. For example: a network diagram or relevant configurations. – YLearn Aug 19 '15 at 4:02
  • i have the same problem as well. what i did was as below which didnt work: route-map nat match ip address 1 access-list 1 permit 192.168.1.0 access-list 1 deny [public IP] ip nat inside source route-map nat interface gi0/0 0verload still not working as customer can go to the internat but the IP is my WAN ip and not customer Public IP. – user22514 Feb 1 '16 at 18:57
  • Please post a new question, @Nemat – Teun Vink Mar 3 '16 at 6:01
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I am not sure if this is recommended but yes you can achieve it.

The reason you needed NAT there as you cant assign same subnet's IP on R2's access facing LAN interface, if you could , then you could use the same subnet , right?

192.168.1.1/24 .2/24
R1(PE -ISP) ------> R2 (CE) -----> R3 (access- internal)

So, you can achieve it by BVI, config is as below, its simple

bridge irb
bridge 1 protocol vlan-bridge
bridge 1 route ip



interface FastEthernet0/0
 no ip address
 duplex auto
 speed auto
 bridge-group 1
!
interface FastEthernet0/1
 no ip address
 duplex auto
 speed auto
 bridge-group 1


interface BVI1
 ip address 192.168.1.2 255.255.255.0

you can change the IP address and interface as per your scenario.

Let me know if any question/issue or how it goes. Sorry, if i misunderstood your question.

Regards, Lalit

  • Hi, Thanks for the reply. My requirement is just simple as If I want to use any of the public IP inside my LAN how to do that? I mean to say for example I am using host A with ip address of 172.x.x.x subnet and that works just fine. But If I just change the IP address of host A to 203.x.x.x subnet will it work too? – Sayeed Aug 18 '15 at 11:18
  • Hello Sayeed, Not until your CE router(connecting to ISP), has two L3 interface one to ISP and one to LAN, so you need to create a BVI and you can do. That's what i explained it earlier with config example. In your example, config would be as below: bridge irb bridge 1 protocol vlan-bridge bridge 1 route ip interface FastEthernet0/0 Desc ** Connecting to ISP*** no ip address duplex auto speed auto bridge-group 1 ! interface FastEthernet0/1 desc ** Connecting to LAN** no ip address duplex auto speed auto bridge-group 1 interface BVI1 ip address 203.x.x.x 255.255.255.0 – Lalit1112 Aug 18 '15 at 11:33
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Sayeed the best approach would be to configure NAT statements that map the public addresses on the outside to the inside addresses on your network. It's not recommended to have host machines configured with public IP addresses. This would be considered a static NAT. I don't have nor have I ever used a Cisco 2900 series router so I can't contribute the exact code to do it. You should be able to google your model and get the configuration guide and I can almost guarantee a section will cover performing static NAT.

You would then configure access lists that specify what addresses on the internet can reach the device and could granularly restrict that to just specific ports.

The devices you configure with the static NAT would always show the same public IP address when seen from the internet.

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