Re: Adoption Call for <draft-troan-6man-universal-ra-option>

[Gyan Mishra <[e-mail]>]

Quick comment.

SLAAC and DHCPv6 play well together in my experience, however I think the
playing well maybe vendor implementation specific.

The M/O bits control stateful nature and various bit combinations, however
for simplicity as long as M=1 a managed address is sent by DHCP relay &
reply back to the hosts on the subnet.

As for SLAAC, the router prefix and Default route is sent via the RA, and I
believe most vendors have that knob enabled by default.

So hosts get both a stateful I believe Windows flags as “public” address as
well as a SLAAC address.

Windows dos prompt  command
“netsh interface ipv6 show address”

“netsh interface ipv6 show interface <index>“ shows the M/O bits received
and cached by the host.

There is a vendor specific knob “ipv6 be default no-advertise” which
disabled SLAAC so the host only gets DHCPv6 address.

Without the knob disabled the host gets both addresses and then used
Default address selection to pick which to use.

As long as the subnet is a /64 as SLACA has the /64 RFC 4862 requirement
then all 3 addressing methods static, DHCPv6 and SLAAC can live together on
the same subnet.

Kind Regards

Gyan

On Tue, Sep 21, 2021 at 5:13 PM Brian E Carpenter <
[e-mail]> wrote:

> On 21-Sep-21 19:51, Vasilenko Eduard wrote:
> > Hi Fernando,
> > The idea "standardize any remaining" looks good but SLAAC and DHCP are
> so different by architecture that it would not be possible.
> > Example: DHCP is the choice for all types of businesses because of
> traceability (billing, troubleshooting, forensic) but SLAAC is silent in
> principle.
> > Hence, SLAAC would be stuck in use cases where it is enforced by one
> company. If not this support SLAAC would be dead by now.
>
> Absolutely not. It isn't "enforced by one company". It does exactly what
> it was designed
> to do, what we called "the dentist's office scenario" in the early days of
> IPng design, actually modelled mainly on Appletalk. You can hook a few IPv6
> boxes together on a wire and they will start talking to each other using
> SLAAC and link-local addresses. Add a router with a prefix and they will
> start talking to the world using SLAAC and RA. DHCPv6 is completely
> unnecessary until the network reaches a certain level of complexity.
>
> The problem area isn't the simultaneous existence of SLAAC/RA and DHCPv6.
> It's that they don't play well together. Maybe we should restate the
> problem as "how to make SLAAC/RA play together better". And task a design
> team with that problem.
>
> On 22-Sep-21 07:04, Vasilenko Eduard wrote:
>
> > Sorry, I still do not understand why the default router should be on
> DHCP.
> > It is just 1 bit: "I am the router on this link". Almost always
> activated bit. No choice, no parameters. Easy to demarcate between
> different teams.
>
> Well indeed, the value comes when there are several routers (hence
> RFC8028). If you would like an equivalent of that functionality in DHCPv6,
> please specify it.
>
> (And BTW it is, to my understanding, implemented on the host side. If
> operators ask for it, no doubt it will appear on the router side.)
>
> >
> > What is really a challenge: the prefix announced through the particular
> interface ("PIO"). The router should know where is this subnet.
> > If prefix would be delivered through DHCP then the router should snoop
> and appoint the appropriate prefix to the interface.
> > Probably you mean this challenge under the name "default router".
>
> One thing about RFC8028 is that it shows that the phrase "default router"
> is insufficient, because the host needs to know the best router for a given
> prefix, not a general default.
>
> > I propose snooping on the router side to learn prefixes.
> > By the way, IPv4 world does not have any automation here (like snooping)
> - they coordinate it manually between teams.
> > The situation is more challenging for IPv6 - many prefixes need to be
> coordinated. Hence, more importance for automation of this process.
>
> Indeed. I think that is why we had the MIF WG. Any sign of PVDs in the
> real world?
>
>     Brian
>
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*Gyan Mishra*

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