dhcpcd-discuss

On 2/14/2017 6:51 PM, Neal P. Murphy wrote:
> On Tue, 14 Feb 2017 22:26:04 +0000
> Roy Marples <roy@xxxxxxxxxxxx> wrote:
>
> > Hi
> >
> > On 13/02/2017 16:31, Shahid Mahmood wrote:
> > > On Sun, Feb 12, 2017 at 5:12 PM, Roy Marples <roy@xxxxxxxxxxxx
> > > <mailto:roy@xxxxxxxxxxxx>> wrote:
> > >
> > >      Hi Shahid
> > >
> > >      On 10/02/17 15:37, Shahid Mahmood wrote:
> > >      > Hello Roy,
> > >      > Just a quick question on section 17.1.3 of RFC 3315. It states 3
> > >      options
> > >      > available to the client in order to select and Advertise message:
> > >      >
> > >      > --- quote
> > >      >
> > >      >    Upon receipt of one or more valid Advertise messages, the client
> > >      >    selects one or more Advertise messages based upon the following
> > >      >    criteria.
> > >      >
> > >      >    -  Those Advertise messages with the highest server preference
> > >      value
> > >      >       are preferred over all other Advertise messages.
> > >      >
> > >      >    -  Within a group of Advertise messages with the same server
> > >      >       preference value, a client MAY select those servers whose
> > >      >       Advertise messages advertise information of interest to the
> > >      >       client.  For example, the client may choose a server that
> > >      returned
> > >      >       an advertisement with configuration options of interest to the
> > >      >       client.
> > >      >
> > >      >    -  The client MAY choose a less-preferred server if that server
> > >      has a
> > >      >       better set of advertised parameters, such as the available
> > >      >       addresses advertised in IAs.
> > >      >
> > >      > --- end quote
> > >      >
> > >      > Specifically, when does client pick the last option:
> > >      >
> > >      >    -  The client MAY choose a less-preferred server if that server
> > >      has a
> > >      >       better set of advertised parameters, such as the available
> > >      >       addresses advertised in IAs.
> > >      >
> > >      > Also, can application influence this choice (with parameter or
> > >      something)?
> > >
> > >      Currently there is no preference selection available.
> > >      dhcpcd binds the first one received and keeps it. It does not change to
> > >      another lease as such.
> > >
> > >   
> > > It is observed that dhcpc picks the first server if two happen to send
> > > Advertize almost simultaneously.
> > > The first advertize has Pref-Value 250, 2nd one 253. It does not seem to
> > > follow 1st bullet in sec 17.1.3 in RFC 3315.
> > >   
> > >
> > >
> > >      Because dhcpcd can trivially remove the lease it applied, changing to a
> > >      new lease from a new server wouldn't be too onerous. How would you say
> > >      to prefer one over another?
> > >
> > >   
> > > At this point, I just wanted to confirm if the behavior is in accordance
> > > with the RFC.
> > Section 17.1.3 says the client MAY select a better server, not MUST.
> > So yes, in the strict sense dhcpcd is in compliance even though it
> > ignores the option.
> >
> > Making dhcpcd react to a more preferred server right away would be quite
> > easy.
> > Storing the adverts for a period of time and then choosing the more
> > preferred one to bind to would be trickier.
> > Right now, I'm not sure which is the better solution.
> Or maybe something in the middle. Save the first advert received. Then for 2-5 seconds, receive an advert, compare it with the saved advert, and save the 'better' one. At timeout, use the saved advert. Of course, determining 'better' may be the real challenge.
>
> Does it make sense to choose a route now, then later change if a better offer comes along?
>
> N
As per RFC section quoted above:

   -	Those Advertise messages with the highest server preference
        	valueThose Advertise messages with the highest server preference
        	value

Is this a *must* or *may* ?