I own several domains, all hosted with Northhosts, but however I register my domains at GoDaddy (since they're cheaper).
When I receive my 'New Account Information' email from Northosts, they always supply two domains, and GoDaddy always wants me to enter at least two nameservers when changing the nameservers.
I recently renewed an old domain that I have with another provider, and I noticed that they too require/give two nameservers.
What is the reason for this? Why is it not possible to use just a single nameserver?