Hi Lorenzo,

[email protected]<mailto:[email protected]>
Paris Research Center
Huawei Technologies France S.A.S.U.

From: Lorenzo Colitti <[email protected]>
Sent: Friday, July 24, 2026 12:15 PM
To: [email protected]
Cc: [email protected]
Subject: [6lo] DHCPv6 vs GAAO option

draft-ietf-6lo-nd-gaao authors,

Looking at https://datatracker.ietf.org/doc/html/draft-ietf-6lo-nd-gaao-11 
again, I still think that a better choice would be to reuse DHCPv6 instead of 
adding the new GAAO option.

Appendix A.3 shows that in terms of bytes and messages, DHCPv6 with Rapid 
Commit is essentially as efficient as GAAO. The remaining inefficiency 
mentioned in the draft is that currently, DHCPv6 SOLICITs are sent to multicast 
addresses.
[LI] Correct.
This is easy to fix: define a well-known anycast address for the DHCPv6 server 
to use in 6lo deployments (as Esko mentioned at the mic). That will be exactly 
as efficient as the GAAO option if the server is on the first-hop router.
[LI] Yes, could be a solution.
But it could also optionally (or in the future) support scenarios where the 
server is not in the first-hop router. There is already an M bit in the RA that 
I think could be used to signal support for this.
[LI] Possibly.

This seems better than the GAAO option because it does not require defining a 
new protocol and provides additional flexibility. If I'm missing something, or 
if we do not take this approach for some other reason, the draft should explain 
why.
[LI] GAAO is an option in 6LoWPAN ND, not a protocol by itself. As stated 
during the meeting, if you run a 6LoWPAN ND stack, having an additional option 
is ‘cheaper” than running an additional service like DHCP. Agreed, this needs 
to be stated more clearly.
Note additionally that the document suggest the use of GAAO _only_ in 6LoWPAN_ 
deployments and _only_ if addresses are assigned algorithmically. More generic 
assignment policies in 6LoWPAN do need DHCPv6. Agreed that this last sentence 
is not in the document, but we will add it, along with the comments you 
provided above.

Thanks

Luigi

Cheers,
Lorenzo
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