Re: [v6ops] draft-ietf-v6ops-host-addr-availability discussion

["Templin, Fred L" <[e-mail]>]

Hi Brian,

> -----Original Message-----
> From: Brian E Carpenter [mailto:[e-mail]]
> Sent: Monday, November 02, 2015 6:55 PM
> To: Templin, Fred L; Lorenzo Colitti
> Cc: [e-mail]
> Subject: Re: [v6ops] draft-ietf-v6ops-host-addr-availability discussion
> 
> Hi Fred,
> On 03/11/2015 14:59, Templin, Fred L wrote:
> > Hi Brian,
> >
> >> -----Original Message-----
> >> From: Brian E Carpenter [mailto:[e-mail]]
> >> Sent: Monday, November 02, 2015 5:46 PM
> >> To: Templin, Fred L; Lorenzo Colitti
> >> Cc: [e-mail]
> >> Subject: Re: [v6ops] draft-ietf-v6ops-host-addr-availability discussion
> >>
> >> On 03/11/2015 14:31, Templin, Fred L wrote:
> >>> Bumping up one level – is it clear to everyone that it is OK to assign addresses
> >>> taken from a DHCPv6 delegated prefix to the interface over which the prefix
> >>> was received?
> >>
> >> If it was legitimately received, I can't see why it wouldn't be OK.
> >
> > OK. When the DHCPv6 server grants a prefix delegation to the client,
> > the server is asserting that that prefix is unique and is now the sole
> > property of the client. So, when you say legitimately received I
> > agree and that is actually a core requirement of DHCPv6 PD.
> > Otherwise, if the DHCPv6 server gave out duplicate prefixes, the
> > routing system would become hopelessly corrupted and address
> > duplication would be the least of our worries.
> >
> >>> And, that DAD is not required for those addresses?
> >>
> >> How is that safe? What is to stop a host running SLAAC once it
> >> sees that prefix in an RA, and hitting the same IID by chance?
> >> At least you need to specify that the A bit must not be set.
> >
> > I am talking about DAD on interface "A" being the interface over
> > which the client receives the prefix delegation. No other node on
> > interface "A" may use the delegated prefix, and no router on
> > interface "A" may advertise the prefix in an RA. The prefix is the
> > sole property of the client that received the PD, so the client is
> > free to assign addresses without needing DAD.
> 
> That usage of "may" might confuse some people, so let's pretend
> you used a "MUST NOT" construct instead. I could still construct
> a host stack that would ignore the issue: its logic would be
> "I sent an RS and got no RA/PIO with A=1; but I see traffic from
> prefix 2bad:dead:beef::/64, so I'll do SLAAC and DAD in that prefix."

The malicious (or otherwise broken) host 'A' could configure any number
of addresses it likes, but it would do so in a vacuum because ingress
filtering will prevent a packet with a source address from a prefix
belonging to host B from being accepted. So, node B has no reason
to fear address duplication by node A.

Also, what if node B in fact did do DAD and A heard it? What is to stop
A from configuring a duplicate address and trying to use it just to mess
up the legitimate operation of node B?

What you are describing is a broken implementation that could only
be employed by a malicious host, and not something that honors
the standards. Doing DAD is not going to guard against malicious
hosts.

Thanks - Fred
[e-mail] 

> >> Come to that, a manual address might collide.
> >
> > The client itself is the only node that is permitted to assign addresses
> > from the delegated prefix to an interface, so there is no risk of
> > collision unless the client itself is somehow corrupt.
> 
> Or another client on the same LAN gets too clever.
> 
>    Brian
> 
> >
> > Thanks - Fred
> > [e-mail]
> >
> >>     Brian
> >>
> >>>
> >>> Thanks - Fred
> >>>
> >>> From: v6ops [mailto:[e-mail]] On Behalf Of Templin, Fred L
> >>> Sent: Monday, November 02, 2015 5:24 PM
> >>> To: Lorenzo Colitti
> >>> Cc: [e-mail]
> >>> Subject: Re: [v6ops] draft-ietf-v6ops-host-addr-availability discussion
> >>>
> >>> Hi Lorenzo,
> >>>
> >>> Responses below in “green”:
> >>>
> >>> From: Lorenzo Colitti [mailto:[e-mail]]
> >>> Sent: Monday, November 02, 2015 5:04 PM
> >>> To: Templin, Fred L
> >>> Cc: Fred Baker (fred); [e-mail]<mailto:[e-mail]>
> >>> Subject: Re: [v6ops] draft-ietf-v6ops-host-addr-availability discussion
> >>>
> >>> On Tue, Nov 3, 2015 at 8:59 AM, Templin, Fred L <[e-mail]<mailto:[e-mail]>> wrote:
> >>> I have one text addition suggestion and one question. On P. 7, in Table 1,
> >>> suggest adding a new final row as follows:
> >>>
> >>>   requires DAD               Yes                  Yes                   No                 N/A
> >>>
> >>> Meaning that multi-addresses configured by SLAAC or DHCPv6 IA_NA/IA_TA
> >>> must use DAD to check for duplicates on the link they were obtained. In a
> >>> multi-addressing environment where millions of addresses are required,
> >>> this could amount to a substantial amount of DAD multicast traffic. On the
> >>> other hand, DAD is not needed for DHCPv6 PD because the network has
> >>> unambiguously delegated the prefix for the node's exclusive use.
> >>>
> >>> I don't think "Requires DAD: No" is correct. Even if the device gets a /64 prefix entirely for its own use, it still needs to do DAD with
> >> any other devices on that /64 (e.g., tethered devices, VMs, etc.).
> >>>
> >>> I'm not opposed to adding a line to the table, though I don't think it provides much value - if we put our mind to it, I'm sure we
> could
> >> come up with lots of things we could add to the table that aren't there at the moment. My main concern is that if we add
> something to
> >> the table it needs to be correct.
> >>>
> >>> What I mean is “Requires DAD on the interface over which the prefix was received”,
> >>> but that was too long to fit in the table. Let’s call the interface “A”. If the node gets
> >>> SLAAC addresses or DHCP IA_NA/IA_TA addresses over interface “A”, then it needs
> >>> to do DAD on interface “A” for each such address. If the node gets a DHCPv6 PD
> >>> over interface “A”, however, it does not need to do DAD over interface “A” at all.
> >>>
> >>> If the node assigns the delegated prefix to interface “B”, then you are right that
> >>> that DAD will be required among all tethered devices, VMs, etc. on interface “B”.
> >>> But, there will still be no need for DAD on interface “A”. Does that clarify?
> >>>
> >>> I have a question also on table 1. Under ""Unlimited" endpoints", why does
> >>> it say "no" for DHCPv6 PD? I think it should say "yes" instead, since a prefix
> >>> obtained by DHCPv6 PD can be used to configure an unlimited number of
> >>> addresses on the link over which the prefix was received.
> >>>
> >>> The table is written from the perspective of the network assigning addresses to devices that connect to it. Therefore, it says "no"
> >> because if you use DHCPv6 PD you can't assign address space to an unlimited number of endpoints - you are limited to however
> many
> >> /64s you have available.
> >>>
> >>> If you use IA_NA or SLAAC, any network with a /64 subnet has, at least in theory, an "unlimited" number of addresses to assign to
> >> clients. Of course, that's only true in theory. In practice, there's going to be a limit due to scaling reasons.
> >>>
> >>> I don’t understand this. True that SLAAC and DHCPv6 IA_NA/IA_TA can be used
> >>> to assign an unlimited number of addresses to interface “A”. But, so can DHCPv6
> >>> PD. When the node receives the delegated prefix (e.g., a /64), it can assign as
> >>> many unique IPv6 addresses as it likes to interface “A”. And again, it need not
> >>> do DAD for any of them.
> >>>
> >>>
> >>>
> >>> _______________________________________________
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> >>> [e-mail]
> >>> https://www.ietf.org/mailman/listinfo/v6ops
> >>>
> >