Re: [OPSAWG] [Add] 🔔 WG LC: RADIUS Extensions for Encrypted DNS

["Joe Clarke (jclarke)" <[e-mail]>]

For an operator standpoint, it seems this point may not be clear enough in the draft and at the very least would likely benefit from some text to call out the limitation.

Joe

From: [e-mail] <[e-mail]>
Date: Thursday, October 13, 2022 at 3:41 AM
To: Ben Schwartz <bemasc=[e-mail]>, Alan DeKok <[e-mail]>
Cc: Joe Clarke (jclarke) <[e-mail]>, [e-mail] <[e-mail]>, [e-mail] <[e-mail]>, [e-mail] <[e-mail]>
Subject: RE: [Add] [OPSAWG] 🔔 WG LC: RADIUS Extensions for Encrypted DNS
Hi Ben, all,

This specification targets typical broadband services in which the use of ECH is not relevant. It does not make sense for ISPs to be hosting multiple domains on the same IP address as the encrypted DNS resolver.

Cheers,
Med

De : Add <[e-mail]> De la part de Ben Schwartz
Envoyé : mercredi 12 octobre 2022 19:54
À : Alan DeKok <[e-mail]>
Cc : Joe Clarke (jclarke) <[e-mail]>; [e-mail]; [e-mail]; [e-mail]
Objet : Re: [Add] [OPSAWG] 🔔 WG LC: RADIUS Extensions for Encrypted DNS

A practical limit of around 4000 octets for SvcParams seems likely to be fine.  A hard limit of 250 octets has a real chance of becoming a practical problem.  I would encourage you to reconsider the format.

As a concrete example, SvcParams are used to deliver public keys for ECH.  Currently, only elliptic-curve keys are used, but if a future iteration relied on RSA public keys, they would not fit within this limit.

On Wed, Oct 12, 2022 at 1:41 PM Alan DeKok <[e-mail]<mailto:[e-mail]>> wrote:
On Oct 12, 2022, at 1:32 PM, Ben Schwartz <bemasc=[e-mail]<mailto:[e-mail]>> wrote:
>
> The Encrypted-DNS-SvcParams TLV seems to be limited to 253 octets.  This is a problem, since it is meant to hold a SvcParams object that is allowed to be much larger (up to ~65000 octets in principle).

  The length is less than 253 octets, as it is encapsulated inside of another attribute "wrapper".  So the practical limit is probably 250 or less.

  RADIUS provides for encoding more than 253 octets in an attribute.  See https://www.rfc-editor.org/rfc/rfc8044#section-3.16

  However, this capability exists only for "top level" attributes, and cannot be used here.

  Further, RADIUS packets are generally limited to 4K octets total.  So even if the limits on this attribute are removed, then there's still a practical limit of around 4000 octets.

  Alan DeKok.

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