Comment 14 for bug 1531103

In IPv6 case, 2::0001 and 2::1 are both valid representation (though 2::1 is a recommended way) and they are identical. IMHO neutron should normalize IPv6 addresses and treat these two as same. That is, even when either of them or other identical addresses are specified, 2::1 should be returned as gateway_ip.

I don't think we should reject an address like 2::0001.

Regarding API backward compat, I am not sure changing 2:0001 to 2::1 is backward incompatible.
I think we have two options: the one is to return normalized IPv6 address, and the other is to return IPv6 address as specified but treat them equally inside neutron. It depends on how we should handle the address format strictly. Personally I am okay to normalize IPv6 address in a response.

In IPv4 case, 1.0.0.001 is rarely used and it is reasonable to consider it as invalid.