IDNA 2008 Question Re: "Confusable" Characters in Domain Names

Shawn Steele Shawn.Steele at
Thu Nov 4 21:40:47 CET 2010

I’d like to throw in my 2 cents.  Clearly a browser has no clue if the DNS layer is operating under IDNA2003 or IDNA2008 rules, nor even if the current browser supports post-IDNA2008 rules (like characters new to Unicode since IDNA2008).  Particularly since different zones could operate under different rules.  I think it’s likely that some browsers will have a relaxed set of rules, since strict adherence to any particular version would likely break names/zones, whether future or old.  The existence of UTS#46 seems to support the idea that some flexibility is desired.

IMO it’s not the client’s responsibility to say whether DNS rules are being followed, but rather the DNS layer’s responsibility to correctly resolve names and provide the appropriate errors when the name isn’t valid.


From: idna-update-bounces at [mailto:idna-update-bounces at] On Behalf Of Vint Cerf
Sent: Poʻakolu, Nowemapa 03, 2010 10:58 AM
To: taliskermoon at; idna-update at
Subject: Re: IDNA 2008 Question Re: "Confusable" Characters in Domain Names

If your browser is operating under purely idna2008 rules the lookup should fail. But some implementations may permit the lookup without verfying the legality of the characters in the lookup string. V

From: idna-update-bounces at<mailto:idna-update-bounces at> <idna-update-bounces at<mailto:idna-update-bounces at>>
To: idna-update at<mailto:idna-update at> <idna-update at<mailto:idna-update at>>
Sent: Wed Nov 03 13:14:55 2010
Subject: IDNA 2008 Question Re: "Confusable" Characters in Domain Names
Dear List Members,

I am a little unclear what impact the IDNA 2008 policy will have on
domain name registrant's who have a domain that does not fall under
the policy's permissible code-points, particularly symbol-based domain

The IDNA 2008 protocol clearly explains what code point are permissible,
but what (in practice) will it mean if someone types in e.g. €.com in their
browser under IDNA 2008?

I do realise that an error message may be displayed, but will IDNA 2008
allow the domain name registrant to satisfy the user's query by forwarding
them on to a different (legal) domain name?

I will hope to hear any replies on this matter.


John Daw
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