Understanding VM Networking

Prerequisites

1. You’ve installed the Anka Virtualization package
2. You’ve created your first VM Template
3. You grasp how to modify VM settings (like network)

The Basics

By default Anka VMs use a shared networking configuration with the host. This uses a combination of NAT with a local DHCP server provided by macOS, but adds a custom layer that we have more control over.

Checking network configuration for VMs

Stopped VM

❯ anka show 12.6 network
+------------+------------+
| mode       | shared     |
+------------+------------+
| controller | virtio-net |
+------------+------------+

Running VM

Every time you start/resume a VM it will be assigned an IP (may take a few seconds for the VM to boot and assign):

❯ anka show 12.6
+---------+--------------------------------------+
| uuid    | 1948dd37-e8ea-43b3-972f-b91860329eab |
+---------+--------------------------------------+
| name    | 12.6                                 |
+---------+--------------------------------------+
| created | Oct 12 17:14:31 2022                 |
+---------+--------------------------------------+
| vcpu    | 5                                    |
+---------+--------------------------------------+
| ram     | 6G                                   |
+---------+--------------------------------------+
| display | 1024x768 vnc://192.168.64.6:5900     |
+---------+--------------------------------------+
| disk    | 200GiB (17.20GiB on disk)            |
+---------+--------------------------------------+
| addons  | 3.1.0.148.6247878                    |
+---------+--------------------------------------+
| network | shared 192.168.64.6                  |
+---------+--------------------------------------+
| status  | running since Oct 14 10:28:54 2022   |
+---------+--------------------------------------+

❯ anka show 12.6 network
+------------+-------------------+
| mode       | shared            |
+------------+-------------------+
| controller | virtio-net        |
+------------+-------------------+
| ip         | 192.168.64.6      |
+------------+-------------------+
| mac        | ae:86:1c:97:a5:8a |
+------------+-------------------+

Types of networking available

These are set using anka modify. Please review the previous section to understand how modifying a VM works.

If anka show does not display an IP, networking has either:

1. Not fully started (give it a few more seconds).
2. Networking cannot start due to some sort of host firewall or policy.

Within the VM, you can find an IP assigned for the host which can be used to ssh or transfer files out. To determine which IP is assigned to the host, execute ipconfig getoption en0 server_identifier (typically 192.168.64.1 for shared network mode and 192.168.128.1 for host network mode).

MAC Addresses

Anka will dynamically assign MAC addresses to your VM. You can assign a fixed MAC Addresses with the anka modify {VM} network --mac {mac address}.

Starting in Anka 3.4.2, you can assign a fixed MAC Addresses and use shared networking to run multiple VMs with the same MAC address. We will handle the dynamic IP assignment for each VM and not let DHCP try to assign the same IP to multiple VMs. This allows you to run licensed software that’s fixed to a specific MAC inside of VMs and not have them conflict with each other.

Be aware that if you clone your VM Template with a specific MAC, both VMs cannot run at the same time.

When using bridged networking mode for your VM, dynamic MAC Addresses are not guaranteed to be unique, though, reuse/collision is extremely unlikely. We do our best to prevent this with our randomization logic.

Default NAT Subnet

VMs are created using the default NAT subnet which can be found with sudo defaults read /Library/Preferences/SystemConfiguration/com.apple.vmnet.plist Shared_Net_Address.

To change this, you can use sudo defaults write /Library/Preferences/SystemConfiguration/com.apple.vmnet.plist Shared_Net_Address -string 192.168.80.1. Changing the Shared_Net_Mask is also available with the same modification to the plist.

DHCP Lease Time

MacOS sets the DHCP timeout to 86,400 seconds (one day) by default. We reuse these leases, which means you will not run out after ~253 VMs in a day. From our testing, Anka’s VM networking is much more stable because of this, and not subject to sudden network reconnections and failed tests when the leases timeout. You can check the amount of leases available with cat /var/db/dhcpd_leases.

Security

We find that many users are interested in VM to VM isolation, VM to Host isolation, and ARP Spoofing prevention. Most macOS virtualization tools on the market do not support network security outside of the defaults Apple provides. We’ve included features to protect from all three in Anka for both Intel and ARM/Silicon.

IP Filtering

Starting in Anka 3.3, users can use a VM/Template specific network traffic filtering which mimicks the behavior of ipf.conf.

This is only available for shared networking.

Filter rules are checked in descending order, with the first matching rule determining the treatment of the packet. For example, the following rules will block any traffic and ignore all other rules:

block any
pass out from all

Examples of rules you can set on a VM:

block out to 1.1.1.1 from any
block out to 1.1.1.1 port 53
block in to port 22
block out from port 68 to port 67
block in from any port 67 to any port 68
block any from port 67 to port 68
block any
block local

You can apply rules in several ways:

1. Globally for all VMs that run on the host by setting the path to the rules file: anka config net_filter /Users/myUser/vm-filter-rules. This will be ignored if the VM Template has filter rules applied already.

2. With a dynamic file from the host, set in the specific VM template, which is then applied at VM start time. This allows you to create rules specific to a VM + Host.

   ❯ cd ~; cat << EOF > ./rules
   pass in from 10.20.30.40
   pass out to 10.20.30.40
   block any
   EOF
   
   ❯ anka modify 13.3.1 network --filter rules
   
   ❯ anka show 13.3.1 network -f                                                                            
   pass in from 10.20.30.40
   pass out to 10.20.30.40
   block any
   
   ❯ cat ~/Library/Application\ Support/Veertu/Anka/vm_lib/c12ccfa5-8757-411e-9505-128190e9854e/config.yaml | grep net
   network_cards:
     controller: virtio-net
     net_filter: /Users/nathanpierce/rules
   

3. Embedding the rules inside of the VM’s config, but not require a file on the host. This is useful to avoid having to ensure the rules file exists on each host.

   ❯ cd ~; cat << EOF > ./rules
   block in from any port 22
   block local
   EOF
   
   ❯ anka modify 13.3.1 network -f- < rules
   
   ❯ anka show 13.3.1 network -f           
   block in from any port 22
   block local
   
   ❯ cat ~/Library/Application\ Support/Veertu/Anka/vm_lib/c12ccfa5-8757-411e-9505-128190e9854e/net_filter 
   block in from any port 22
   block local%
   

4. You can also apply a single rule using echo "block any" | anka modify 13.3.1 network -f-.

Applying new rules will remove all previously set.

You can disable the rules with anka modify 13.3.1 network --filter off.

VM to VM isolation

This requires using IP Filtering features available for shared networking mode. To prevent VM to VM communication, you will use block local.

VM to Host isolation

This requires using IP Filtering features available for shared networking mode. To prevent VM to Host communication, you will use block local.

ARP Spoofing Prevention

ARP Spoofing is prevented by default for all networking modes except for nat.

ARP Isolation is not blocked however. You can run sudo arp -a for example and see the other VMs running on the host and their MAC and IP. You can prevent this with network --no-local, but keep in mind this also disables VM to Host and VM to VM communication.

FAQs

• Should your Firewall software be blocking VM networking, you need to whitelist the /Library/Application\ Support/Veertu/Anka/bin/headless.app (3.x), /Library/Application\ Support/Veertu/Anka/bin/ankahv.app, and /Applications/Anka.app.

What’s next?

• Activating your Anka License
• Anka Command-Line Reference