Subject: Re: [Emu] EAP and Fragmentation

From: John Mattsson <[email-masked]>
Date: Sun, 10 Mar 2019 12:39:53 +0000

Welcome and thanks for your comments Oleg!

slon v sobstvennom palto <[email-masked]>; wrote:

>Per my experience the existing fragmentation method described in EAP-TLS
>RFC 5216 serves good for all fragmentation needs. The method is reused by
>PEAP, EAP-FAST, TEAP and EAP-TTLS. There's an ambiguity in EAP-TLS RFC that
>doesn't specify whether a not-fragmented message should have the L bit and
>the 4 octets length field so different peers treat it differently. However,
>for example, EAP-TTLS RFC closed it tightly saying that even a
>single-fragment message should have it nevertheless on its redundancy.

I cannot find anything in EAP-TTLS (RFC 5281) saying that the L bit should be set. As you have noticed, EAP-TLS (RFC 5216) does not say anything about the L bit in unfragmented messages and my understanding is that the ambiguity is if unfragmented messages can (not should) have the L bit set. As far as I can see, EAP-TTLS (RFC 5281) states that unfragmented messages MAY set the L bit.

RFC 5281 Section 9.2.2:

   “Unfragmented messages MAY have the L bit set and include the
    length of the message (though this information is redundant).”

I looked through the other TLS-based EAP methods (both RFCs and drafts) and none of them seems to say anything new about the L bit. draft-ietf-emu-eap-tls13 should clarify any ambiguity.

Should draft-ietf-emu-eap-tls13-04 just copy the sentence from RFC 5281 or do the group want something different?

Cheers,
John

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From: slon v sobstvennom palto <[email-masked]>
Date: Thu, 14 Mar 2019 17:11:54 +0200

Hi John,

>Should draft-ietf-emu-eap-tls13-04 just copy the sentence from RFC 5281 or
do the group want something different?

I remember that some EAP-TLS/PEAP clients rejected not fragmented messages
without L bit set, probably due to their wrong interpretation of EAP-TLS
RFC. Would it worth to say something like "Implementation SHOULD accept
unfragmented messages with and without L bit set" in addition to copying
the sentence above from RFC 5281?

Cheers,
Oleg

On Sun, Mar 10, 2019 at 2:39 PM John Mattsson <[email-masked]>
wrote:

> I cannot find anything in EAP-TTLS (RFC 5281) saying that the L bit should
> be set. As you have noticed, EAP-TLS (RFC 5216) does not say anything about
> the L bit in unfragmented messages and my understanding is that the
> ambiguity is if unfragmented messages can (not should) have the L bit set.
> As far as I can see, EAP-TTLS (RFC 5281) states that unfragmented messages
> MAY set the L bit.
>
> RFC 5281 Section 9.2.2:
>
> I looked through the other TLS-based EAP methods (both RFCs and drafts)
> and none of them seems to say anything new about the L bit.
> draft-ietf-emu-eap-tls13 should clarify any ambiguity.
>