Glue records….i wonder WHY most of Engineers, DNS specialist call them as Advanced DNS stuff!
i totally disagree to it …..
as per me:
Glue records – MOST fundamental DNS record which actually start the lookup!
Lets understand how to come in basic scenario……
Observe two sites – harisri.in & anuragbhatia.com
There’s a basic difference in terms of DNS in both sites. Nameservers of harisri.in are ns1.anuragbhatia.com & ns2.anuragbhatia.com which belongs to a totaly seprate zone, but nameservers for anuragbhatia.com are ns1.anuragbhatia.com, ns2.anuragbhatia.com & so….. i.e domain is having nameservers which are sub zones of domain itself.
Working of DNS in both cases
Query for ns starts:
ISP->Root servers-gtld servers->returing ns – ns1.anuragbhatia.com, ns2.anuragbhatia.com and so with ip’s 126.96.36.199, 188.8.131.52…….
and thus got ip of resolvers…..so work of DNS is over.
Now observe route for DNS lookup of harisri.in
Query for ns starts:
ISP->root server->cc tld server- in servers->returning ns – ns1.anuragbhatia.com & ns2.anuragbhatia.com
Now important here is nameservers are given in form of hostnames (NOT ip) and thus a lookup will continue for resolving ns1.anuragbhatia.com and so in way as
ns1.anuragbhatia.com – seprating ns1. and lookng for anuragbhatia.com, got nameservers – ns1.anuragbhatia.com, and ns2.anuragbhatia.com with ip’s and now on those dns servers query will ask for ip for ns1.anuragbhatia.com (confusing here? …yes i know!)
This means if we want to get ns for anuragbhatia.com we will get ns1.anuragbhatia.com & ns2.anuragbhatia.com with ip’s BUT if we want ns for harisri.in, we will get ns in hostnames and a seprate lookup will be done to resolve those hostnames and important is ….whenever a domain has nameservers of any other domain, then nameserver’s host names are resolved on dns of 2nd and NOT via glue records……..
Thus now we can understand glue records as the MOST fundamental dns records which provide glue for a hostname on root servers.
And interesting fact is glue records are on root servers and NOT dns servers, though we MUST have corresponding A records on DNS hosting for every glue record.
A more interesting thing about these records is these have many names as per different registrars…….some call it nameservers records, some call it child nameservers, some give it as option for registering nameservers etc.
Thus a nameserver woeks with three most fundamental records:
- Glue records (on root server of that tld)
- A records corresponding to glue on dns host
- NS records at dns host for deligating zone on those specific servers.
Are glue records essential part of DNS?
Yes! they are…..you can have your site working without any glue records but at the end the nameservers you are using must have glue, e.g you can have nameservers of your site as ns1.your-web-host.com and your-web-host.com might have namesevers dns1.nameserver.com and then namesevers.com will be having ns1.nameserver.com thus….at last glue is on ns1.nameserver.com
How many glue records one can create?
Its virtually infinite but you might experience issues becoz of registrar limits.
Glue records, much similar to A records, can i use them as substitute to A records?
No, no and NEVER think of that.It will not work, as i already said that we MUST have A records entries for every glue record, thus as general glue records without any a is virtually nothing.
I guess reason for its not working can be to prevent load on root servers, like if that way is allowed then people might use too many glue records without giving any load on their dns servers!
I can’t see any option like glue records in my domain control panel. What to do?
Is it necessary to have glue records if i want to use hostnames as nameservers for domains?
Confusing question, for now my answer is yes. I have tried using hostnames on name.com and Direct i when i didn’t had any glue records, all worked fine but when i tried entering those as namesevers for a domain on eNom, it gave errors.
i had nameservers like ns21.anuragbhatia.com & ns22.anuragbhatia.com which have A entried on namserver hosting anuragbhatia.com itself. And finally when i provided glue to those nameservers, they worked fine with eNom also. Thus thats all depends on regitsrar’s policies, and it will be always better to have glue for nameserver records.
What will happen if we have un-matched set a record and glue records for a given hostname?
Nothing will wrk!
i mean to say you will get arbit results. In fact a few months back it took me 1hr to find out a similar issue where i get different ip for a hostname from different locations. So all i can say – be careful!!!