Re: [Ntp] New rev of the NTP port randomization I-D (Fwd: New Version Notification for draft-gont-ntp-port-randomization-01.txt)

[Fernando Gont <[e-mail]>]

On 29/5/19 01:21, Harlan Stenn wrote:
> 
> 
> On 5/28/2019 10:20 PM, Harlan Stenn wrote:
>>
>>
>> On 5/28/2019 9:37 PM, Fernando Gont wrote:
>>> On 28/5/19 23:20, Majdi S. Abbas wrote:
>>>> Fernando,
>>>>
>>>>     Randomizing the source port is pointless.  As Danny has noted, t1 already acts as a 2^64 nonce on each client mode chime request.  This sufficiently hardens the unauthenticated case to an off path attacker.  If additional security is required, authentication (via classic PSK, or NTS modes) should be used.
>>>>
>>>>     Per session randomization doesn't resolve these issues -- the stated rationale for both the draft and filed CVE is hardening to off path attacks, which we've just covered.
>>>>
>>>>     "Because it's best practice" isn't a reason -- it's a crutch to save a draft that was filed due to an insufficient understanding of RFC 5905 and current implementations of NTPv4.  
>>>
>>> Oh, by the way. While you enlighten me why you need a fixed well-known
>>> port number for the client, and how necessary this is, please also
>>> elaborate on how I'm running multiple NTP clients behind a NAT box.
>>
>> Nobody seems to be saying there is benefit to *only* using the
>> well-known port number when sending a client request.  People are saying
>> that requiring this in all cases doesn't buy any significant benefit.
> 
> I was unclear above - "this" refers to always requiring a random port
> for sending client requests.

The draft says "SHOULD" -- i.e., do it unless you have a very good
reason not to.

Thanks,
-- 
Fernando Gont
SI6 Networks
e-mail: [e-mail]
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