A single global outside address and multiple PAT static addresses. Is this possible?

Robert Hatcher
Robert Hatcher used Ask the Experts™
on
Our company is running out of IP addresses. We have several class C subnets. One is dedicated to switch maintenance. I can't get another public subnet and the present switch subnet is too full. We will need another 124 managable switches we call internal switches.  They willl handle only private static addresses. I came up with a technique to have a private unique address that follows the publics first octet with that octet swapped to an equivelant 10 subnet. The two middle octets are the same as the public switch addresses. We wish to have a close to possible maintenance access and track syslog and snmp data as our public switches operate.

I would like to take a Cisco router and set it up with a global single outside address and many private NAT-ed addresses. So far everything I am reading seems to require one each public and NAT-ed private scenario. I would need 124 global addresses to handle 124 NAT-ed addresses. I am hoping there is a way.

Outside.x.y.z:61 - NAT - Inside.x.y.61
Outside.x.y.z:62 - NAT - Inside.x.y.62
etc.

Please let me know if you need more detail or if I am going about this wrong. I am not allowed to use a firewall.
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Distinguished Expert 2018
Commented:
Yes, it is possible. (if this is what you are asking for Port address transition).

ip nat inside source static tcp Inside.x.y.z1 61 Outside.x.y.z 61 extendable
ip nat inside source static tcp Inside.x.y.z2 23 Outside.x.y.z 62 extendable

Inside.x.y.z1 - inside IP address                   61 - inside port
Outside.x.y.z - outside IP address               61 outside port
keyword extendable is needed to permit traffic from a single WAN IP address to mutiple inside IP addresses
Robert HatcherSystem Admin and Network Engineer

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Commented:
The number "23" I assume that is a typo sir? You meant "62"?
Distinguished Expert 2018
Commented:
No, you can use any port you want. Does not need to be 1:1

you can have
ip nat inside source static tcp 192.168.0.1 80  1.1.1.2 80 extendable
ip nat inside source static tcp 192.168.1.1 80  1.1.1.2 81 extendable
ip nat inside source static tcp 192.168.2.1 80  1.1.1.2 82 extendable
ip nat inside source static tcp 192.168.3.1 80  1.1.1.2 83 extendable

outside port 80 will be forwarded to 192.168.0.1 port 80
outside port 81 will be forwarded to 192.168.1.1 port 80
outside port 82 will be forwarded to 192.168.2.1 port 80
outside port 83 will be forwarded to 192.168.3.1 port 80

You can do as you wish.

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