Traffic rules

Hangar watches every Hangar Managed VM from the Mac, outside the guest, so software in the VM can't hide from it: DNS lookups, connections with their host names (from DNS, TLS and HTTP), bytes in and out, and what was blocked. For HTTPS it sees the host name, not the URL.

In the app, open a VM's Traffic tab; its Rules section edits the lists.

Modes

Rules

A rule is a host with its subdomains (github.com), only its subdomains (*.github.com), or a network (140.82.112.0/20). Rules apply to a running VM at once.

With an allow or block list, other VMs, services on this Mac and your local network (every private address, like 192.168.1.0/24) are blocked unless you allow them (--vms on, --host on, --local-network on); an allowed network such as 192.168.1.20 opens just that part.

QUIC (HTTP/3) is blocked in these modes too unless you allow it (--quic on), because it hides host names, and --udp off blocks all UDP but DNS through this Mac.

Try it

hangar traffic kestrel --follow
hangar policy kestrel --mode allowlist --allow github.com --allow '*.npmjs.org'
hangar policy kestrel --udp off
hangar policy kestrel --isolate on

02:39:41  allow  tcp     github.com           140.82.121.3:443     ↑2 KB ↓570 KB
02:39:42  BLOCK  dns     example.com A                             example.com is not allowed
02:39:43  BLOCK  udp     1.1.1.1              1.1.1.1:443          QUIC is blocked

In every mode, off included, Hangar drops frames in which a Hangar Managed VM claims another MAC or IP address, and DHCP replies sent by VMs, so one VM can't take over another's traffic.

Isolate

Isolate cuts the VM off from everything but this Mac. The shared clipboard and shared folders still work.

hangar policy kestrel --isolate on

Rules files

A VM's rules can be saved and shared as a JSON file: the mode, the allowed and blocked hosts, and what the VM may reach. Isolation isn't part of it.

In the VM's Traffic tab, Rules File exports the rules, or imports them from a file or from an https:// address (Import… › Import from URL…). Hangar shows what would change and asks before it replaces anything.

{
  "allowed": ["github.com", "*.npmjs.org"],
  "allowsHost": false,
  "allowsLocalNetwork": false,
  "allowsQUIC": false,
  "allowsUDP": true,
  "allowsVMs": false,
  "blocked": [],
  "mode": "allowlist"
}

A file can be at most 1 MB, and a VM can have at most 1000 rules. Ready-made files for Claude Code, Codex, CI runners and more, and a builder for your own, are in Policies.

Limits

• The allow list is the protection. A block list only stops connections that name a blocked host, so a program that connects to an address directly, with another host name or none, gets through.
• A host behind the same CDN address as an allowed one may be reachable. For HTTPS and for HTTP connections upgraded to WebSocket, Hangar checks the name the connection opens with, not what is sent inside it.
• With an allow or block list, DNS goes only through this Mac; in the allow list mode DNS over TCP is blocked. IPv6 is dropped in every mode. monitor records everything and blocks nothing.
• A VPN that routes Hangar's subnet without giving this Mac an address in it isn't noticed; if VMs lose connections while a VPN is on, move Hangar's network (hangar network set --subnet).
• Hangar doesn't watch or check VMs on NAT, so they can pretend to be each other's address on the system's NAT network.