House, job and kennitala

Hi all!
I will move to Iceland nex September. I have a question: when do I have to apply for a "long term" kennitala? I know european citizens can stay in Iceland looking for work up to 6 months, but isn't clear if the kennitala is issued
1) Immediately
2) As soon you have a residency (but to rent a flat do you will need a kennitala?)
3) As soon as you find a job (isn't unclear if the employer have to do this for you)

Can anyone help me? I am very confused, of course I will ask as soon I will be in Reykjavik, but goin with some ideas wil help.
Thank you!

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