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Why was edns created ?

Earlier versions of DNS had some restrictions that wouldn't allow new features of DNS to get implemented.

What kind of restrictions does DNS have ?

Size restrictions.

Size of what ?

Flags, response codes and label types.

How does EDNS resolve that ?

If the client has EDNS support, it will add the new fields in the "Addtionnal Data" section with a specific pseudo-resource-record (pRR ?) of type OPT. Since this RR is purely fabricated by the server, it doesn't live in any zone file or database, that's why it's called a pseudo resource record. Older servers will simply ignore this field because it is of an unknown type to them, and new servers will understand them. Also, new servers won't send OPT type pRR unless it was present in the request, thus avoiding to confuse older clients.

What are some cool features provided by EDNS that weren't possible without it ?

DNSSEC


contact : @ychaouche yacinechaouche at yahoocom


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