I've introduced today a new DNS check (Glue Mismatch) under NS section. While querying nameservers often they do provide A or AAAA records in additional section of the response to help/speed up host name resolution, those records are named glue records.

You can examine a DNS query to see glue records from command line with dig:

[[email protected] ~]$ dig mx redhat.com @ns1.redhat.com

; <<>> DiG 9.3.6 <<>> mx redhat.com @ns1.redhat.com
;; global options:  printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 2912
;; flags: qr aa rd; QUERY: 1, ANSWER: 2, AUTHORITY: 3, ADDITIONAL: 5

;; QUESTION SECTION:
;redhat.com.                    IN      MX

;; ANSWER SECTION:
redhat.com.             600     IN      MX      5 mx1.redhat.com.
redhat.com.             600     IN      MX      10 mx2.redhat.com.

;; AUTHORITY SECTION:
redhat.com.             600     IN      NS      ns2.redhat.com.
redhat.com.             600     IN      NS      ns3.redhat.com.
redhat.com.             600     IN      NS      ns1.redhat.com.

;; ADDITIONAL SECTION:
mx1.redhat.com.         600     IN      A       209.132.183.28
mx2.redhat.com.         600     IN      A       66.187.233.33
ns1.redhat.com.         600     IN      A       66.187.233.210
ns2.redhat.com.         600     IN      A       209.132.183.2
ns3.redhat.com.         600     IN      A       209.132.176.100

;; Query time: 150 msec
;; SERVER: 66.187.233.210#53(66.187.233.210)
;; WHEN: Wed Nov  3 15:05:56 2010
;; MSG SIZE  rcvd: 202

In this example while querying MX records from ns1.redhat.com I've received the IP addresses of the mail exchangers:

mx1.redhat.com.         600     IN      A       209.132.183.28
mx2.redhat.com.         600     IN      A       66.187.233.33

Sometimes you may mess up IP addresses for your nameservers (example IPs provided by your nameserves are different by IPs provided by your registrar), this new check should catch this problem.

Check your domain's glue records here:

http://www.dnsinspect.com