how to create a perl hash?

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Perl

my %hash1 = {a=>192.168.0.1,b=>192.168.0.1,c=>192.168.2.2,d=>192.168.2.3,e=>192.168.3.4,f=>192.168.3.4};

I have perl hash like given above. keys are device names and values are ip addresses.How do i create hash with no duplicate ip addresses (like %hash2) using %hash1(devices that have same ips are omitted.)?

my %hash2 = {c=>192.168.2.2,d=>192.168.2.3};