We are configuring one customer with two ISPs and the customer is not having his own AS and Public IP. ISPs are not ready to advertise other ISPs public ips.
The solution which comes in my mind is NAT. Customer private LAN will be natted to ISPs public IPs and the packets will be forwarded to respective ISPs.
Please advise if the above solution will work? if yes, then will both links be used as backup to each other? If some other option is also avaialble.
Load balancing is impossible in this case, you can only do load sharing by manipulating the weights of the routes received from the 2 providers to prefer some routes over one provider and other routes from the other provider while still redundant to each other, if you are going to receive full routing table then see this example i liked its logic (1->128 through ProviderA, and others are preferred over providerB), this is your best bet:
NOTE: Multipath can be used for multiple links from the same provider and can't used with multiple providers, as for the maximum-paths feature to operate, all attributes must be identical and the next-hop must be different (although we can use the hidden command bgp bestpath as-path multipath-relax to allow the router to load-share across multiple BGP paths even if the as-path is different but i've never tried this my self).