Re: [TLS] Short notes on TLS RFCs ...

On Fri, Jun 20, 2014 at 9:15 AM, Michael Tuexen
<Michael.Tuexen@lurchi.franken.de> wrote:
> On 20 Jun 2014, at 05:32, Colm MacCárthaigh <colm@allcosts.net> wrote:
>
>>
>> 3. The purpose of heartbeat message seems to be a form of path MTU
>> discovery, but they also seem ill-suited to MTU discovery. In
>> particular, Heartbeat messages seem to me capable of only discovering
>> the lowest-MTU supported in both directions of transmission; rather
>> than the actual MTU of the network paths; which can be (and sometimes
>> are) asymmetrical.  This may seem very esoteric, but as WANs and
>> transit providers deploy jumbo-frames inconsistently, asymmetrical
>> MTUs are becoming more common. Though hopefully that day will pass.
> No, heartbeat messages contain a payload being reflected and a padding
> being discarded. Therefore you can send your (large) probe packet
> containing a relatively small payload and a padding to get it to
> the size you want to test, and just get back a small answer containing
> the payload (and a small padding). So the padding is there especially
> for dealing with asymmetric paths.

So Heartbleed is a feature: send a small packet and get a large
response for the direction you want to test.

Sincerely,
Watson Ladd
>
> Best regards
> Michael
>>
>> Again, apologies if my notes are duplicative, but figured it was
>> better to report a dupe than to miss something.
>>
>> --
>> Colm
>>
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>
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