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Re: [babel] Comments about rfc7298bis

Juliusz Chroboczek <jch@irif.fr> Mon, 07 May 2018 14:24 UTC

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Date: Mon, 07 May 2018 16:24:45 +0200
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From: Juliusz Chroboczek <jch@irif.fr>
To: Denis Ovsienko <denis@ovsienko.info>
Cc: Babel at IETF <babel@ietf.org>
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Subject: Re: [babel] Comments about rfc7298bis
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> Regarding your recent concerns about 7298-bis data items not fitting
> into output packets, the task of fitting protocol data items into
> a packet buffer is neither new nor really difficult.

I think got it, sorry for being so slow.  Contrary to what I believed,
7298bis only requires TS/PC sub-TLVs to be included in existing IHUs.  It
does not require a full set of TS/PC sub-TLVs to be included in every
packet.  See Section 5.4 point 4 -- it only requires rejecting packets if
there's no sub-TLV in a matching IHU.  On the other hand, if a packet does
not include a matching IHU, then it is accepted as soon as the TS/PC TLV
(not sub-TLV) is good.

Is that right, Denis?

If so, then I'd like to understand why this is safe.  Intuitively, I'd say
that by allowing packets without a matching TS/PC sub-TLV, replay attacks
might still be possible.  Now, the MUST in Section 3.4.3 of 6126bis
should mitigate most such attacks, but I'm still a little worried.

Denis, can you please point me where you explain why accepting packets
with no matching TS/PC is safe?

-- Juliusz

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