NAT'd Subnet and Public Subnet on Same vLAN

Question:

I hope this finds you WS-C3560V2-48PS-S  well. A quick message to pick your brains if I may with a current issue I have on my Cisco 2921 router.

In short, we have two physical interfaces - one internal (0/2), one external (0/0). The internal interface has several sub-interfaces of which one has a Public Subnet applied to it (0/2.100), and another sub-interface has a NAT'd Subnet applied to it (0/2.101).

The traffic from the NAT'd subnet (0/2.101) appears online as the Public IP Address on the first physical inteface (0/0), as expected, when you lookup your Public IP Address online. We need to move this NAT'd Subnet to appear as one of the Public IP Addresses from within the other sub-interface (0/2.100).

My question is, how would I achieve this. This is the current configuration including the two physical interfaces, and the two sub-interfaces:

interface GigabitEthernet0/0

ip address 31.210.XX.XX 255.255.255.248

ip nat outside

ip virtual-reassembly in

duplex auto

speed auto

!

interface GigabitEthernet0/2

no ip address

duplex auto

speed auto

!

interface GigabitEthernet0/2.100

encapsulation dot1Q 100

ip address 31.210.XX.XXX 255.255.255.240

!

interface GigabitEthernet0/2.101

encapsulation dot1Q 101

ip address 192.168.1.254 255.255.255.0

ip nat inside

ip virtual-reassembly in

To summarise, we would like the NAT'd sub-interface (0/2.101) to use one of the IP Addresses in the other sub-interface (0/2.100) as it's Public address. I hope that makes sense, thanks in advance for your help and of course ask any further questions you may have!

All the best,

Matthew

Answer:

you will have to create a nat pool to get the desired result.

sample configuration. WS-C3560V2-48PS-S Price

ip nat pool Net31 31.210.x.x 31.210.x.x netmask 255.255.255.240

ip nat inside source list 1 pool Net31 overload

access-list 1 permit 192.168.1.0 0.0.0.255