Re: [homenet] New Version Notification for draft-barth-homenet-wifi-roaming-00.txt

Tore Anderson <tore@fud.no> Mon, 30 November 2015 13:08 UTC

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Date: Mon, 30 Nov 2015 14:08:39 +0100
From: Tore Anderson <tore@fud.no>
To: Steven Barth <cyrus@openwrt.org>
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Subject: Re: [homenet] New Version Notification for draft-barth-homenet-wifi-roaming-00.txt
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* Steven Barth <cyrus@openwrt.org>

> here is some attempt to formalize a simple WiFi roaming approach
> using host routes and a stateless proxy for DAD NDP messages.
> 
> It's a bit theoretical right now but may be useful as a start for a
> discussion. We could do a talk on it in Yokohama as well.

Hi Steven and thanks for this! It's a problem it's important to solve.

Some questions/thoughts after a very quick skim through:

>      A router MUST listen for all Neighbor Solicitations with a target
>      addresses from an assigned roaming prefix having the unspecified
>      address as the source address.  Similarly it MUST listen for all
>      Neighbor Advertisements with a target address from an assigned
>      roaming prefix and having the all-nodes multicast address as the
>      destination address.
>
>      A router MUST forward all such messages via global unicast to all
>      other routers having roaming interfaces sharing the roaming
>      prefixes the target address of the respective message belongs to.

(Similar language in section 3.2.)

Do I understand correctly that this will only happen for NS packets
destined for the globally scoped address? That is, no proxying of the
DAD messages for link-local addresses? Assuming clients don't re-start
DAD after having roamed from one BSS to another, isn't that a problem?

>     The IPv6 address fe80::1 SHOULD be used as fixed link-local
>     address exclusively by the router on roaming interfaces.

Isn't a more appropriate address to use for this the subnet-router
anycast address, i.e., fe80::? See RFC4291 section 2.6.1 - the intended
usage seems to be quite fitting for your use case:

   The Subnet-Router anycast address is intended to be used for
   applications where a node needs to communicate with any one of the
   set of routers.

Finally:

>     Stateful DHCPv6 MUST NOT be used to avoid the need to synchronize
>     lease information and relay DHCPv6 packets.

What about DHCPv6 Prefix Delegation? Not supported? I think there is a
use case for supporting PD to wireless clients if possible (think
virtual machines, 464xlat, etc.)

Tore