jarl/docs/views.md

Split DNS with views

Views let named answer differently depending on who asks. The usual setup for a homelab that is also authoritative on the internet has two views:

• internal: your networks get recursion (they use the server as their resolver) and see private addresses (nas.adbraun.lol → 10.10.0.20) and internal-only zones such as reverse zones for private networks.
• external: everyone else gets authoritative answers only. That means public addresses, no recursion, and no internal zones.

How named treats views (and why Jarl asks to move your zones)

Without any view statements, named puts every zone into an implicit default view. That's why an imported server shows no views. As soon as one view exists, named requires every zone to be inside a view. So the first view you create has to take over the existing zones, including the root hints zone . that Debian/Ubuntu configure.

Jarl does this in the same changeset that creates the view:

• web UI: Views → New view. The box "Move the N zone(s) that are not in a view into this view" is ticked by default.
• CLI: jarl view create NAME --adopt-zones
• API: "adopt_zones": true

Creating the first view without it is refused before anything reaches named (zone_outside_view).

Views are matched in order: the first view whose match-clients (and match-destinations) fit the client wins. Put the specific view first and the catch-all last.

Step by step

1. Check the ACL for your networks

The internal view matches your networks. Usually that's the ACL you already use for allow-recursion:

jarl acl list
jarl acl update homelab --add localhost      # if missing; see the note below

Include localhost if the DNS server itself uses 127.0.0.1 as its resolver. Otherwise the server's own lookups land in the external view and get no recursion.

2. Create the internal view and move the existing zones into it

jarl view create internal --match-clients homelab --adopt-zones --dry-run   # look first
jarl view create internal --match-clients homelab --adopt-zones

create view internal
move zone . into view internal
move zone 0.10.10.in-addr.arpa into view internal
move zone adbraun.lol into view internal
applied (changeset 4)

Nothing changes for your clients: they match internal and get the same answers as before. The server-wide options (recursion, allow-recursion, forwarders, ...) still apply, because views inherit them.

3. Create the external view

jarl view create external --match-clients any
jarl option set recursion no --view external
jarl option set allow-recursion '{ none; }' --view external

The inherited allow-recursion { homelab; } already keeps outsiders from recursing. The explicit recursion no also stops them reading the cache, and makes the intent obvious. Setting allow-recursion { none; } as well avoids named-checkconf's warning that allow-recursion is still active in a view with recursion off. Jarl warns (security_open_resolver) if a view ever offers recursion to everyone.

Jarl counts the external view as reachable from the internet (its match-clients end in any) and checks it: rate limiting, ANY queries, the version string and more. See the Exposure page or jarl exposure, and exposure.md to set up response rate limiting.

4. Give the external view its zones

Mostly the same, a few differences (split DNS). Create the external copy linked (below): Jarl keeps the shared records the same in both views, and each view can have records of its own:

jarl zone create adbraun.lol --view external --link-with internal
jarl record set adbraun.lol www A 203.0.113.20 --view external --local   # public address, external only
jarl record delete adbraun.lol nas-internal A --view external            # gone from both: it was shared

Delete records you don't want outside before you link, or make them local to the internal view first (jarl record update ID --local): a shared record is in both views.

Two separate copies. --clone-from copies the zone once; from then on the two are separate zones, and a record added to one isn't in the other:

jarl zone create adbraun.lol --view external --clone-from adbraun.lol --clone-view internal

The same data in both views. Use an in-view zone. The external view then serves the internal view's zone, so there is one copy to maintain:

jarl zone create example.org --view external --type in-view --in-view internal

Don't do that for zones with private data. Internal-only zones (reverse zones for 10.x / 192.168.x) simply don't get an external copy: named answers outsiders with NXDOMAIN from its built-in empty zones.

5. Check from both sides

dig @ns1.adbraun.lol nas.adbraun.lol +short            # from the LAN: 10.10.0.20
dig @<public-ip> nas.adbraun.lol +short                 # from outside: 203.0.113.20
dig @<public-ip> example.com                            # from outside: status REFUSED
jarl check

On the server, dig -b <source address> picks which view you test, or, from anywhere, sign the query with the view's key (below):

jarl view key external --named-conf > external.key
dig -k external.key @ns1.adbraun.lol nas.adbraun.lol +short   # 203.0.113.20, even from the LAN

View keys

named picks a view by where a query comes from, so a query this server sends to its own public address usually lands in the internal view: its source is one of your own networks. That makes checks of the external view from the server itself (such as Jarl's delegation check) see the wrong view.

So Jarl gives every view a TSIG key, jarl-view-NAME, and puts it at the front of the view's match-clients:

view "internal" {
	match-clients { !key jarl-view-external; key jarl-view-internal; homelab; };
	...
view "external" {
	match-clients { key jarl-view-external; any; };

A query signed with a view's key lands in that view, whatever its source; the !key stops an earlier view from taking a later view's queries. Clients don't send these keys, so for them nothing changes. Jarl signs its own queries to this server's addresses with the key of the zone's view. The keys live in keys.conf with your other keys, never in diffs or in jarl tsig list; their secrets are derived from a random value in Jarl's database (and in its backups), so they stay the same from one apply to the next. jarl view key VIEW shows one (it needs tsig:write and is audited). Key names starting with jarl-view- are reserved, and the view keys can be used in your own options (allow-transfer { key jarl-view-external; }).

Linked zones

Most split-horizon zones are the same in every view apart from a few names. Linking zones of the same name in different views lets Jarl keep the shared records in step, while each view can still have records of its own and its own zone options.

• Shared records are in every linked view. Adding, changing, disabling or deleting one in any view does the same in the others, in the same changeset: the diff shows every view, and history, undo and jarl check treat them together.
• Local records are in one view only (--local, or Only here in the web UI). A local record overrides the shared records of the same name and type in that view: www A 10.0.10.5 local to internal, while the external view keeps the shared www A 203.0.113.20. Delete the local records and the view gets the shared ones back.
• A new record joins the set of the same name and type: local if that set is local in its view, shared otherwise.
• Sharing a version (jarl record update ID --shared, Share in the web UI) makes that view's records of that name and type the shared version: the other views' records of that name and type are replaced.
• Zones stay separate in named, so each keeps its own serial, options (allow-transfer, DNSSEC signing, ...) and file, and the views keep their own match-clients, recursion and order.

jarl zone link adbraun.lol --view internal --with external   # link two existing zones
jarl zone create adbraun.lol --view vps --link-with external # a new zone, linked from the start
jarl record list adbraun.lol --view internal                 # LINK column: shared or local
jarl record add adbraun.lol nas A 10.0.10.20 --view internal --local
jarl record update 1234 --local                              # this name and type: only this view
jarl record update 1234 --shared                             # this view's version, everywhere
jarl zone unlink adbraun.lol --view vps                      # records stay, all local

Linking never changes what named answers. A name and type with the same records in every view becomes shared; one that differs stays local to each view (Jarl lists them). Share the right version afterwards. Unlinking keeps every record, all local; a link left with one zone is dissolved, as when the other zone is deleted.

Permissions are checked in every view a change reaches. A token with a grant for one view only (views=internal) can change that view's local records and make overrides, but not a shared record, since that would change the other views too: Jarl says so and suggests a local record. A grant without a view (the usual zones=adbraun.lol) covers every view.

Importing a zone file into a linked zone (jarl zone import) adds the records like any others: shared, unless the name and type is local there. With --replace, shared records missing from the file are deleted in every linked view.

ACME challenges are written once per link, and so reach every linked view; jarl acme, lego's httpreq and certificates Jarl obtains all do this.

Compared with BIND's in-view, where one view serves another's zone as it is: linked zones can differ per view, keep their own options, and don't depend on the view order (in-view can only use a view defined before it).

Living with views

• Commands that name a zone that exists in several views need --view (jarl record add adbraun.lol www A ... --view external). Jarl refuses to guess.
• jarl acme writes challenge records into every view that has the zone, so Let's Encrypt (external) and internal clients see the same thing (once per link, for linked zones). Use --view to limit it.
• --view all (or a list) on record commands changes each linked zone once: the change reaches the others through the link. With --local it goes to each view named.
• jarl view order internal external changes the match order, and jarl view list shows it.
• Deleting a view is refused while it still has zones, unless you pass --cascade.
• Each view has its own page (Views → the view's name): its settings, options and zones.
• Give each view a colour (the view's page → Settings → Colour, or jarl view color internal green) to tell the zones of each view apart in the zone list. The colour only affects the web UI, so it applies at once, with no changeset or deploy. jarl view color internal default goes back to the link colour.
• Zone files are stored per view: /var/lib/bind/jarl/internal/adbraun.lol.zone, /var/lib/bind/jarl/external/adbraun.lol.zone.