Resolver source port behaviour checker
In light of the CERT VU#800113 announcement, DNS-OARC has created a special DNS name and server that you can query to determine if your resolver is at risk.
dig @184.108.40.206 +short porttest.dns-oarc.net TXT
Replace 220.127.116.11 with your resolvers address. The result will either return FAIR, GOOD or POOR based on the observed deviation of the source ports.
Full details of DNS-OARC test can be seen here.