diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 91d999c..a7b708a 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -18,7 +18,7 @@ jobs:
 
       - name: Download datasource
         run: |
-          curl https://iptoasn.com/data/ip2asn-combined.tsv.gz | gunzip -c | tee data/ip2asn.tsv
+          curl https://iptoasn.com/data/ip2asn-combined.tsv.gz | gunzip -c | dd status=none of=data/ip2asn.tsv
 
       - name: Build dataset
         run: |
@@ -27,6 +27,6 @@ jobs:
       - uses: eine/tip@master
         with:
           tag: "nightly"
-          token: ${{ github.token }}
+          token: ${{ secrets.GITHUB_TOKEN }}
           files: |
             ./data/ipasn.mmdb
diff --git a/cmd/ipasn/ipasn.go b/cmd/ipasn/ipasn.go
index 49d6f68..d7c66e9 100644
--- a/cmd/ipasn/ipasn.go
+++ b/cmd/ipasn/ipasn.go
@@ -12,6 +12,7 @@ import (
 	"strconv"
 
 	"github.com/maxmind/mmdbwriter"
+	"github.com/maxmind/mmdbwriter/inserter"
 	"github.com/maxmind/mmdbwriter/mmdbtype"
 )
 
@@ -43,11 +44,8 @@ func main() {
 			continue
 		}
 
-		start := net.ParseIP(record[0])
-		end := net.ParseIP(record[1])
-		asn, err := strconv.ParseUint(record[2], 10, 32)
-
-		if start == nil || end == nil || err != nil {
+		start, end, asn, name := parseRow(record)
+		if start == nil || end == nil {
 			log.Printf("Invalid IP range: %s - %s %s", record[0], record[1], record[2])
 			continue
 		}
@@ -56,12 +54,10 @@ func main() {
 			continue
 		}
 
-		name := record[4]
-
-		if err := writer.InsertRange(start, end, mmdbtype.Map{
+		if err := writer.InsertRangeFunc(start, end, inserter.TopLevelMergeWith(mmdbtype.Map{
 			"asn":  mmdbtype.Uint32(asn),
 			"name": mmdbtype.String(name),
-		}); err != nil {
+		})); err != nil {
 			log.Printf("%s - %s %s", record[0], record[1], record[2])
 			log.Println(err)
 			continue
@@ -77,3 +73,27 @@ func main() {
 		log.Fatal(err)
 	}
 }
+
+func parseRow(record []string) (net.IP, net.IP, uint32, string) {
+	start := net.ParseIP(record[0])
+	end := net.ParseIP(record[1])
+	asn, err := strconv.ParseUint(record[2], 10, 32)
+
+	if start == nil || end == nil || err != nil {
+		return nil, nil, 0, ""
+	}
+
+	if asn == 0 {
+		return start, end, 0, ""
+	}
+
+	// map 6to4 address back to IPv4
+	// if start[0] == 0x20 && start[1] == 0x02 {
+	// 	start = net.IPv4(start[2], start[3], start[4], start[5]).To4()
+	// 	end = net.IPv4(end[2], end[3], end[4], end[5]).To4()
+	// }
+
+	name := record[4]
+
+	return start, end, uint32(asn), name
+}