I was looking at the Linode DNS manager for my domain, and I am quite confused on something.

I set the nameservers to linodes nameservers with my domain registrar.
This means that DNS is managed by linode, and I configure my CNAME, A records, etc. with linode.

But why does linode also allow me to set NS Records?
I though the NS records were only set with the domain registrar.

The NS records are used to delegate what Name Servers are authoritative (have the answers) for a domain or subdomain.

Setting the Name Servers at your registrar are glue records, so the root servers know where to direct DNS queries to your authoritative name servers. If you local DNS resolver doesn't know the answer to your DNS query it will query the root servers, to where it can find the answer.

Take a look at http://en.wikipedia.org/wiki/Domain_Nam ... ue_records

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Travis

This doesn't really have anything to do with glue records.

When you set your nameservers at your registrar, you're telling the registry (Verisign in the case of .com) which nameservers should handle queries for your domain.

When you set nameservers in the Linode DNS manager, you're specifying which nameservers Linode should report as authoritative for your domain. This is one step down the chain of authority from the registry.

Normally you want to leave the NS records in the Linode manager alone; after all, if Linode alone is handling your DNS queries, the zone should reflect that. The only time you would need to change it is if you have other, non-Linode servers that are sharing your DNS duty, as part of a master/slave configuration. This is a somewhat advanced technique, and if you're not sure if you need to do this, you definitely don't.

Glue records are unrelated, and exist to tell the registry's DNS servers which IP address(es) a given nameserver should resolve to. This only ever matters if example.com is using a subdomain of itself (e.g. ns1.example.com) as a nameserver, and eliminates the circular dependency that would otherwise be created.