$TTL 1H
@		IN SOA		ns.example.com. root.example.com. (
				2015121600	; serial
				6H		; refresh
				1H		; retry
				1W		; expiry
				1D )		; minimum
		IN NS		ns.example.com.
1		IN PTR		somehost.example.com.
2		IN PTR		anotherhost.example.com.
# ...
130		IN PTR		example.com.
# ...