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

[Ted Lemon <[e-mail]>]

Right, think of a snac router with three uplinks as being similar to a home network with three uplinks. We haven't entirely solved that problem, so trying to solve it here in snac-simple would be... ambitious. :)

I'd love to work on that, but let's do what we know how to do first. 

On Wed, Apr 15, 2026, at 9:07 AM, Esko Dijk wrote:
> Thanks, now we have ample home network case study documentation to read 
> on a train trip to Vienna :)
> 
> > So they get the highend SNAC-router that can plug into three AIL,
> > perhaps via USB ethernets.   That seems like a reasonable thing to me.
> 
> FYI the OpenThread Border Router implements a SNAC router that limits to 
> only one AIL interface. Maybe that's our typical SNAC-simple case? But 
> in general, for a high-end Linux based device it's easy to plug in 
> USB-Ethernets which then may get to do something.
> 
> (That starts to feel like doing HomeNet all over again, weirdly enough, 
> because I wasn't even active in that WG...)
> 
> Esko
> 
> 
> On 4/14/26 20:17, Michael Richardson wrote:
> > Esko Dijk <[e-mail]> wrote:
> >      > 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.
> >
> > Unless this CE is one of mine, wouldn't the WiFi and Ethernet be bridged by
> > the CE, so it's really all one AIL in that 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.
> >
> > Okay, I accept this.
> >
> > I guess I'd think it was more sensible to plug the travel router into my LAN,
> > where the existing CE would bridge it to the existing WiFi, bringing all my
> > house back online.  Of course, that results in dualing DHCPv4 servers, but
> > IPv6 ought to work fine.  The existing CE *ought* to withdraw it's GUA v6
> > prefixes via a zero-lifetime RA when it sees it has no uplink.
> > Of course, if it's the CE that fails, then the bridging won't work, OTH, there won't
> > be dualing DHCPv4 servers.
> >
> > {I don't know if any actually do.  For me, that would be undesired, as I'd
> > lose local routing during the three-times weekly outages of PPPoE
> > thanks to incumbent telco incompetence  (aka enemy action IMHO. I'm not with
> > incumbent telco, but they "own" the wires, and control the PPPoE PAD redirector)
> > Mind you, I use a statically delegated v6-prefix rather than a PD
> > one... because PD wasn't implemented when we started.  I actually get a PD
> > one too, but ignore it.}
> >
> >      > In both cases, the SNAC router has 2 AILs active at the same time so it's not
> >      > an either-or situation.
> >
> > We did go through this (multiple-uplinks, multiple CE) extensively in HOMENET
> > ages ago, and this certainly was a situation which a lot of people cared
> > about.  But, still not fully solved.
> >
> >      >> 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.
> >
> > If the SNAC router is the only device connected to both AIL, is it doing
> > enough DNS-SD and/or mDNS collision helping so that the two printer.local
> > have found themselves unique names?   Like, what if there are answers from
> > both AIL?
> > Or maybe this is all really irrelevant to SNAC??  (... as the doorbells should just
> > use the printers in the nearby ICE van)
> >
> >      >> > 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!
> >
> > aulx. . o O ( "C> COPY myletter.txt AUX:" ... Amiga could do same. )
> >
> >      > 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.
> >
> > +100
> >
> >      > - 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.
> >
> > okay.
> > I also wonder about multi-tenant Small-Office IoT situations.
> > Like, the hair dresser and talent agent occupy the front and back of a
> > streetfront, but do not share Internet with the web designer/building owner
> > who lives upstairs.   But, they all should be able to adjust lighting, heat,
> > and the like.  Being reasonable friends, there are no authorization
> > complexities.  (No they don't share printers, there is no routing)
> >
> > So they get the highend SNAC-router that can plug into three AIL,
> > perhaps via USB ethernets.   That seems like a reasonable thing to me.
> >
> >  From what I am understanding there is nothing that keeps the SNAC-router from
> > offering it's generated ULA on more than one AIL.  There are probably
> > subtle complexities when one AIL has an infrastructure v6 prefix and another
> > does not.
> > And... first PD wins with hystersis to avoid frequent renumbers of the Stub
> > Network?   Does the delegated prefix from AIL-1 get RIO's onto the other AIL?
> >
> >      > - 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
> >
> > +1
> >
> > I'm not hearing a huge argument for new text for snac-simple.
> > It's been enough months since I've been immersed in the document, that I am
> > having to go back to make sure I'm using the right terms.
> >
> > --
> > Michael Richardson <[e-mail] <mailto:[e-mail]>>   . o O ( IPv6 IøT consulting )
> >             Sandelman Software Works Inc, Ottawa and Worldwide
> >
> > **       My working hours and your working hours may be different.         **
> > ** Please do not feel obligated to reply outside your normal working hours **
> >
> >
> >
> >
> 
> -- 
> Snac mailing list -- [e-mail]
> To unsubscribe send an email to [e-mail]
>