Hi Jaime,
Thanks a lot for your review. Please see my comments and responses inline below.
On Thu, Jun 4, 2020 at 9:58 AM Jaime Jimenez via Datatracker <noreply@xxxxxxxx> wrote:
Reviewer: Jaime Jimenez
Review result: Ready with Nits
draft-ietf-dhc-slap-quadrant-07 iodir review
============================================
This draft is complementary to draft-ietf-dhc-mac-assign. It defines mechanisms
to allow for the use of IEEE's SLAP quadrant when using DHCP for MAC
allocation. It also defines a new DHCPv6 Option (QUAD) for that purpose.
Both drafts verse on the use of DHCP to assign MAC addresses to hosts, which as
a concept was strange to me to begin with. However I am not up-to-date in the
latest developments on host configuration so I am likely to be missing a big
part of the picture.
I find this draft quite useful to understand the rationale behind
draft-ietf-dhc-mac-assign, and I regret not having paid more attention to it
before I did the draft-ietf-dhc-mac-assign review. At the time I understood the
rationale to be the use of MAC address as a deployment mechanisms while in
reality, it is a privacy mechanism. I think the security scenario makes more
sense as IoT devices normally are deployed with MAC information from the
factory. I believe that is the primary purpose of both dhc-slap-quadrant and
draft-ietf-dhc-mac-assign when it comes to IoT, perhaps that information should
be emphasized on draft-ietf-dhc-mac-assign.
This draft is clearly written and seems ready, below are few concrete comments:
Abstract:
Consider splitting in two shorter sentences the paragraph below.
" [...] Recently, the IEEE
has been working on a new specification (IEEE 802c) which defines a
new "optional Structured Local Address Plan" (SLAP) that specifies
different assignment approaches in four specified regions of the
local MAC address space."
[Carlos] Done. Changes applied in -10 version (to be released after collecting all comments from IESG review).
Section 1:
s/specified regions/regions/ ?
"different assignment approaches in four specified regions of the"
[Carlos] Since IEEE 802c also defines the regions, we believe it's better to keep the original wording to make this more explicit.
Section 3:
"[...] if the IoT device can move, then it might prefer to
select the SAI or AAI quadrants to minimize address collisions
when moving to another network."
I wonder if collisions are likely to occur in practice.
[Carlos] Collisions are always possible, since devices can always select their own address without using a delegation mechanism, but not very likely. draft-ietf-dhc-mac-assign has some security considerations about address collisions.
Section 4.1:
Naive questions on MAC usage. Could an IoT device self-assign a MAC with a
specific SLAP quadrant information? Would the DHCP Server accept it without
the negotiation mechanisms described here (providing it is not in the MAC
address pool)? Could an endpoint use an OUI from a different vendor? If so,
how are potential collisions or attacks preventable?
[Carlos] It is always possible that a device self-assigns a MAC address from any quadrant, though for some quadrants it is not the expected use (therefore, if a device does it, it would not be behaving as specified). draft-ietf-dhc-mac-assign has some security considerations about address collisions that would apply here as well.
"[...] The server MAY alter the
allocation at this time."
It would be helpful to explain in which way allocation might be altered
(i.e., by reducing the address block)
[Carlos] OK, we have added some examples in -10.
"5. When the assigned addresses are about to expire, the client sends
a Renew message. It includes the preferred SLAP quadrant(s) in
the new QUAD IA_LL-option, so in case the server is unable to
extend the lifetime on the existing address(es), the preferred
quadrants are known for the allocation of any "new" addresses."
Is it correct to assume that step 5 causes either:
- to assign the existing block
- to start on step 1 with the new QUAD if the block is no longer available.
[Carlos] Not sure I got it right, but Step 5 does not cause going back to step 1. It basically includes the preferred SLAP quadrants again to facilitate the server allocating _different_ addresses to the ones the client got assigned, in case the server cannot extend the lifetime of these ones (e.g., because of a renumbering policy).
So, is it then the case that the client sends a Renew message -for the
existing block- with _alternative_ SLAP quadrants different than the ones
in use in case the block is no longer available?
[Carlos] Please check if my response beforer clarifies this.
"6. The server responds with a Reply message, including an LLADDR
option with extended lifetime."
What happens with the _fail_ case, in which the block is no longer
available? How is the REPLY format denying the addresses?
[Carlos] In this case the client would know by checking the allocated address(es) (if they are different, that means that the addresses are no longer available, and the client would know from which quadrant they belong to, as this is implicit from the address itself)..
A style suggestion, as "Advertise", "Renew", "Reply", etc are specific DHCP
message types, you might want to write them capitalized "ADVERTISE",
"RENEW", "REPLY", etc to avoid potential confusion.
[Carlos] Here we've followed the same approach as in draft-ietf-dhc-mac-assign. If we change it, we should do it in both.
Section 4.2:
"9. When the assigned addresses are about to expire, the client
sends a Renew message.
[...]
12. The relay sends the Reply message back to the client."
Same as in section 4.1, steps 9 to 12 might need to be revised.
[Carlos] Please see if my responses to 4.1 are satisfactory.
Section 7:
The Security section looks a bit thin but I have no good suggestions to
improve. Is it even possible for a bad actor to spoof a RENEW lease on
behalf of another node? Perhaps some information on authentication
mechanisms for DHCP would be handy.
[Carlos] We mainly refer to RFC 8415 and RFC 7227 for all the security mechanisms of DHCP, and also to draft-ietf-dhc-mac-assign for some additional considerations regarding link-layer address assignments using DHCP.
References:
[IEEEStd802c-2017] does not provide a link to the document. It would be
useful to include that when available.
[Carlos] OK, noted. Thanks.
Thanks a lot.
Carlos
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