Re: [TLS] Multiple records in record limit (was: Secdir review)

[Nikos Mavrogiannopoulos <[e-mail]>]

On Mon, 2018-02-26 at 12:39 +1100, Martin Thomson wrote:
> Out of the secdir review (thanks again Alan!), I realized that the
> draft never actually said this:
> 
>    PMTU governs the size of UDP datagrams, which limits the size of
> records, but
>    does not prevent records from being smaller.  An endpoint that
> sends small
>    records is still able to send multiple records in a single UDP
> datagram.
> 
> I think that I should add that explanation.
> 
> Does anyone think that this should go further and advise against
> putting multiple records in the same datagram?

I'm not sure which part of the protocol text this would refer to, but
DTLS1.2 says in https://tools.ietf.org/html/rfc6347#section-4.1.1

```
   Multiple DTLS records may be placed in a single datagram.  They are
   simply encoded consecutively. 
```

so even though I agree that the advice against putting multiple records
in the same datagram is a good one (I'm not even sure if that works
today with existing implementations), the advice seems against the
original protocol. Shouldn't that text be in the upcoming DTLS1.3
rather than an update like record size limit which seems unrelated?

regards,
Nikos