Can Loopback IP be Public

[deepmaterialcn]

If my Access Device need to access the Application which is bound to a loopback IP, the loopback IP need to be a Public IP as well right? Is it possible to have a Public IP for a Loopback that's reachable via ISP1 and ISP2?

However, we want to add another Public Interface via another ISP for Redundancy on the Core Device. The application that resides on the Core Device can only bind to one IP Address which means I have to use a loopback IP Address and have the two Physical Interfaces configured with Public IP1(ISP1) and Public IP2(IP2).

I have a Usecase where an Access Device need to reach a Core Device over the Internet. Access Device is configured with the Public IP of the Core device as of now so that it can reach the Core over the Internet.

[MHM Cisco World]

No Need, 
config the Loopback as private IP 
then use NAT with route-map 
this NAT private IP to Public IP when next-hop is ISP one or other Public IP if the next-hop is IPS two.

[Richard Burts]

It is an interesting suggestion to use NAT with route map. This works well when doing dynamic NAT for inside devices attempting to access resources in the outside. But the diagram in the original post clearly has the access device in the outside and the application is inside. If I understand the original post correctly the access device will originate traffic to the application. For outside to initiate traffic to inside we usually need static NAT. Static NAT with a single ISP is pretty straightforward. But with a second ISP it becomes complicated. 2 ISP suggests 2 Public IP addresses. But how would the access device know which of the 2 addresses to use? Is it possible that the access device could attempt access using the first address and if that did not work would attempt access using the second address?

If that is not possible then my suggestion would be to configure 2 static NAT (one NAT Public IP per ISP) and then to do something with DNS that would track reachability of the first Public IP and if it became unreachable would change DNS to supply the second address. 

[MHM Cisco World]

https://www.cisco.com/c/en/us/support/docs/ip/network-address-translation-nat/100658-ios-nat-load-balancing-2isp.html

You right and there is some restrict for my suggestion.
please find the cisco Doc. about my suggest.

thanks for point me.

[Richard Burts]

Thanks for posting the link. Yes that discussion does present a solution for using NAT with 2 ISP. I have done similar configs and they do work. But it is doing NAT for traffic originated inside and going outside. What this original post is asking is NAT for traffic originated outside and going to inside. This is much more of a challenge.