RE: encoding Subnet ID in link-local addrs (Re: about violation of standards)

["Mudric, Dusan (Dusan)" <[e-mail]>]

> -----Original Message-----
> From: Alexandre Petrescu <[e-mail]>
> Sent: Friday, April 26, 2019 5:02 AM
> To: Mudric, Dusan (Dusan) <[e-mail]>; [e-mail]; Ole Troan
> <[e-mail]>; , <[e-mail]>
> Cc: Pascal Thubert (pthubert <[e-mail]>
> Subject: Re: encoding Subnet ID in link-local addrs (Re: about violation of
> standards)
> 
> 
> 
> Le 25/04/2019 à 16:32, Mudric, Dusan (Dusan) a écrit :
> >
> >> 2 IPv6 link-local addresses are typically self-configured according
> >> to 4 RFCs and relying on the fe80::/10 IANA allocation, RFC 54 0
> >> bits, and RFC MAC-based 64bit Interface IDs.  In some cases, it is
> >> advantageous to manually configure link-local addresses.  This is
> >> useful for easy remembering by humans, and for parameter resilience
> >> during network interface replacement.
> >>
> >> Manual configuration of an LL may use short IID and Subnet ID The
> >> Subnet ID presence in the link-local address is useful in some
> >> wireless settings where the subnet structure parameters depend on the
> >> link locality.  Other settings may also benefit.
> >>
> >> When manually setting the link-local address it is necessary to know
> >> the length of the prefix of the subnet on which this link-local
> >> address is present.  This length is necessary for on-link
> >> determination.
> >>
> > [Dusan] Is the Subnet ID unique per host?
> 
> In  my setting, the Subnet ID in the LL address is unique per subnet, not per
> host.  There is a subnet formed by the front bumper interface in the follower
> car and the rear bumper interface of the lead car.
> 
> The Subnet ID in an LL address would be unique per a set of hosts in that
> subnet.
> 
> > Is it possible that all hosts on the link share the same Subnet ID?
> 
> Yes, they should.
> 
> > Can somebody provide more details about the problem and how this
> > solution will solve the problem?
> 
> More details about the problem: RFC4291 54 0 bits would refuse to change to
> accomodate this solution's Subnet ID in an LL address; another detail is that
> one particular OS would not allow the manual configuration of an LL address
> setting some of these 54 0 bits.
> 
> Alex
> 
> >
[Dusan] These are RFC4291 and OS limitations, if you would define Subnet ID in LL address. Based on the comment above, I gather you are talking about vehicle-
   to-vehicle (V2V) communication. Looks like there are several cars talking to each other on the local link. They form a subnet. Somehow, somewhere, there is a master device that knows this is a subnet. May be that device's link is on the subnet. ...

- Can you please provide more details about the topology first,
- then, details about the restrictions with the current LL definition in that topology,
- then, details about the expected improvements if LL has the Subnet ID?

Once we understand these three categories, we will be able to talk about solutions. May be the solution will be generic enough to help other mobile hosts too, not just V2V.