Re: [Ntp] Antwort: Re: Symmetric mode

[Miroslav Lichvar <[e-mail]>]

On Thu, Sep 29, 2022 at 12:11:51PM -0400, Danny Mayer wrote:
> On 9/26/22 6:53 AM, Miroslav Lichvar wrote:
> > The trouble is that the peer is doing both the client and server part
> > of the protocol at the same time.
> No, and that's the misunderstanding as explained in another message. It's
> either acting as a client or as a server but not both at the same time.

How would they decide which one is a client and which one is server?
The mode number is the same when both are active peers. That is the
point a symmetric association that both are client and server at the
same time and the reason why it is so difficult to implement and
vulnerable to attacks.

> > As you can see, there are 4 client/server mode packets per poll, but
> > only 2 symmetric mode packets per poll.
> 
> There might be a bug in the code, but you should see the same number of
> packets.

It's not a bug. It's by design. If the peers responded immediately, it
would create a flood of packets between them, saturating the network
or CPU.

In Figure 15 of the RFC (describing the state of two peers) you can
clearly see that there are only 2 messages per poll.


                t2      t3                 t6          t7
        ---------------------------------------------------------
                 /\         \                 /\            \
                 /           \                /              \
                /             \              /                \
               /               \/           /                 \/
        ---------------------------------------------------------
             t1                t4         t5                  t8


-- 
Miroslav Lichvar