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

[Esko Dijk <[e-mail]>]

Hi all,

This item was triggered by a private mail exchange with Ted about Github 
issue #152 (Clarify the one-DNS-zone-per-AIL requirement). He said I 
should take it to the list, so here goes :)

What was intended by the draft is now clear to me at least, and I've 
submitted a text change to clarify the intention of the existing draft:

  https://github.com/ietf-wg-snac/draft-ietf-snac-simple/commit/5a8f66178a8db6968aab53bd9673b138bd46b3d7

(accidentally this was pushed to main instead of creating a PR. )


So the idea we had already for a while in SNAC-simple is that a single 
SNAC router can have multiple AIL interfaces, hence connections to 
multiple AILs. This is written in various places in the draft. Ted 
suggested this situation may go beyond what we want to address in 
SNAC-simple -- after all, it's multiple AILs and that complicates 
things.  Even though it's not as problematic as multiple SNAC routers 
each connected to different AILs!

To have a placeholder for this discussion I created now: 
https://github.com/ietf-wg-snac/draft-ietf-snac-simple/issues/180


Do we see any issues or complexities with having multiple AIL interfaces 
on one SNAC router?    From my viewpoint:

1. For IPv6 routability, I didn't see any issue: the SNAC router 
receives a packet and determines the right AIL to forward it to based on 
IP address.

2. For IPv4 routability (via NAT64), the routability looks ok but the 
draft would need to detail how to apply the rules of Section 6 for the 
multiple AILs case. These are currently written as if there's a single 
AIL which is called "infrastructure".

3. For host and service discoverability, multiple AILs implies creating 
multiple DNS domains (each mapping to the .local of one AIL) and also 
may require a technique (supported via a Discovery Proxy) that allows a 
stub network client to unicast a single DNS query referencing a single 
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.)


We may decide to either tackle these details, or update the draft to 
limit the scope to a single AIL only.

best regards

Esko