[Snac] Re: Handling multiple AIL-interfaces in a single SNAC router

[Esko Dijk <[e-mail]>]

On 4/13/26 21:16, Michael Richardson wrote:
>      > router can have multiple AIL interfaces, hence connections to multiple
>      > AILs. This is written in various places in the draft. Ted suggested
>
> Are/do these multiple AILs link up to a single ISP/Infrastructure router?
> Or different ones?

The common case will be the same CE router, connected to the same ISP: 
this is a Wi-Fi plus Ethernet case.

Another, not so common case is when a user has connected the two 
interfaces to different ISPs.  For example, user has a Wi-Fi travel 
router used as an "internet backup" for cases when the regular ISP 
(accessed preferably via e.g. Ethernet) fails. Hotspot is turned on. 
Then, the SNAC router sees the SSID appear, connects via Wi-Fi, and 
finds IPv4 and/or IPv6 internet connectivity via that AIL. Its internet 
access now should be routed via the Wi-Fi AIL while the discovery of IoT 
devices or printers etc. on the Ethernet AIL should still continue.

In both cases, the SNAC router has 2 AILs active at the same time so 
it's not an either-or situation.

>      > domain, which then gets proxied into the multiple DNS zones i.e. executed as
>      > mDNS on all AILs. This is similar to how RFC 8766 says to query on both IPv4
>      > and IPv6 based on a single unicast query.  Also the naming of these multiple
>      > DNS zones may be a topic (marked "WG TBD" currently in the draft.)
>
> So my Thread doorbell ("stub network client") that wants to *print* the
> picture it took, can look up printer.local, and this turns into multiple mDNS
> queries, one on each AIL?
> Is that what this means?
Yes, so the printer can be found on either AIL (e.g. Wi-Fi or Ethernet). 
And on either IPv4 or IPv6.
>      > We may decide to either tackle these details, or update the draft to limit
>      > the scope to a single AIL only.
>
> I think the scope should be limited. This is snac-simple, and I thought it
> was done.  Maybe some thinking goes into snac-many-garlic (AIL = French for Garlic)
> such that if we go there, it doesn't break something else.

Simple as in 1 AIL sounds good here. In botanical French and older 
recipes, apparently multiple ail is written as "aulx". (Les aulx.) Not 
so simple!

Some considerations why 1 AIL may be a perfectly fine limitation:

- for the common case of Wi-Fi + Ethernet and same ISP, the CE router 
may be already doing the bridging of the links or the proxying of mDNS 
between links. So if the SNAC router only uses Ethernet for discovery, 
it will also find a service/host on Wi-Fi.

- vendors may extend SNAC-simple with their own solution for multiple 
AILs (as Ted commented on the Github issue), even when SNAC-simple 
doesn't define that.

- for the case of Ethernet + "backup Wi-Fi" earlier in my mail, the 
discovery only has to work on one AIL (Ethernet) not on the other 
because typically there's nothing to discover there. (Think phone Wi-Fi 
hotspot with client isolation.)

- two Ethernet "uplink" / AIL ports is very rare for a non-CE-router device


Esko