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RE: on-link and off-link

Vasilenko Eduard <vasilenko.eduard@huawei.com> Mon, 12 July 2021 16:14 UTC

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From: Vasilenko Eduard <vasilenko.eduard@huawei.com>
To: "Pascal Thubert (pthubert)" <pthubert@cisco.com>, Philip Homburg <pch-ipv6-ietf-7@u-1.phicoh.com>, "ipv6@ietf.org" <ipv6@ietf.org>
CC: Alexandre Petrescu <alexandre.petrescu@gmail.com>
Subject: RE: on-link and off-link
Thread-Topic: on-link and off-link
Thread-Index: AQHXdyb7YXMuWgk+gkikqI5k+gcOz6s/dH1SgAADpuD//9ZSAIAANLxg
Date: Mon, 12 Jul 2021 16:14:32 +0000
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By the way,
It blocks not just native P2MP technology,
It does break any filtering, like "PVLAN" or "WiFi isolation",
Because if it is not possible to send a multicast to other hosts to check DAD even for LLA.
Ed/
-----Original Message-----
From: Pascal Thubert (pthubert) [mailto:pthubert@cisco.com] 
Sent: Monday, July 12, 2021 7:04 PM
To: Vasilenko Eduard <vasilenko.eduard@huawei.com>; Philip Homburg <pch-ipv6-ietf-7@u-1.phicoh.com>; ipv6@ietf.org
Cc: Alexandre Petrescu <alexandre.petrescu@gmail.com>
Subject: RE: on-link and off-link 

Exactly; the model at the IP layer has to be multilink subnet.
Your link local gets you to a router but not to all in the subnet.

With IPv6 all is abstracted with multicast operations and link local addresses. 
So what IP considers a link and who belongs to a subnet (is constrained by but) does not need to match what the L2 sees, e.g., the L2 links (e.g., an ethernet wire or a radio range) and the L2 broadcast domains (e.g., a 802.1 bridged domain or a Wi-Fi ESS). 
IPv4 gave the wrong habit of thinking they have to be congruent. They don't.

Pascal

> -----Original Message-----
> From: ipv6 <ipv6-bounces@ietf.org> On Behalf Of Vasilenko Eduard
> Sent: lundi 12 juillet 2021 17:35
> To: Philip Homburg <pch-ipv6-ietf-7@u-1.phicoh.com>; ipv6@ietf.org
> Cc: Alexandre Petrescu <alexandre.petrescu@gmail.com>
> Subject: RE: on-link and off-link
> 
> NBMA or P2MP are not supported by IPv6 anyway because it is not 
> possible to check LLA uniqueness - multicast does not work.
> LLA proxy is needed on the hub site.
> Ed/
> -----Original Message-----
> From: ipv6 [mailto:ipv6-bounces@ietf.org] On Behalf Of Philip Homburg
> Sent: Monday, July 12, 2021 6:20 PM
> To: ipv6@ietf.org
> Cc: Alexandre Petrescu <alexandre.petrescu@gmail.com>
> Subject: Re: on-link and off-link
> 
> > I think one question
> > might be: do we agree that each IP address is assigned on an 
> > interface, and thus is on-link on a particular link?
> 
> This is not correct. On a NBMA link it is possible that all GUA 
> addresses are not on-link.
> 
> The conceptual model of on-link is that a host can use neighbor 
> discovery to find an onlink neighbor. If the neighbor is not on-link 
> then traffic has to go (at least initially) through a default router.
> 
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