run: add `--ip-address` option by tofugarden · Pull Request #261 · nirs/vmnet-helper

tofugarden · 2026-07-03T04:01:43Z

Objective

Allow assigning a static IP to a VM started with run. Closes #260.

Implementation notes

Argument validation requires the requested IP to be in the same subnet as the DHCP range as defined by --start-address, --end-address, --subnet-mask. It does not require the address to be outside the range.

The file at testing/validate.py now contains all argument validation functions.

cloud-init supports setting multiple IP addresses, but we only support one command line argument. It wouldn't be that difficult to implement, it's just not needed.

nirs

Tested locally:

Switch from dhcp to ip address

% ./run ubuntu --ip-address 192.168.200.128 --start-address 192.168.200.1 --end-address 192.168.200.127 --subnet-mask 255.255.255.0
[   0.042] INFO Starting vmnet-helper for 'ubuntu' with interface id '6bbc6ce9-5e26-4b39-bc9c-28c88776d519'
[   0.213] INFO Creating cloud-init iso '/Users/nir/.vmnet-helper/vms/ubuntu/cidata.iso'
[   0.235] INFO Starting 'vfkit' virtual machine 'ubuntu' with mac address '82:e9:dd:3d:68:1f'
[   5.080] INFO VM is ready at ubuntu-vmnet-helper.local

% ssh ubuntu -- ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host noprefixroute 
       valid_lft forever preferred_lft forever
2: enp0s1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 82:e9:dd:3d:68:1f brd ff:ff:ff:ff:ff:ff
    altname enx82e9dd3d681f
    inet 192.168.200.128/24 brd 192.168.200.255 scope global enp0s1
       valid_lft forever preferred_lft forever
    inet6 fdd3:28eb:866d:8319:80e9:ddff:fe3d:681f/64 scope global dynamic mngtmpaddr noprefixroute 
       valid_lft 2591905sec preferred_lft 604705sec
    inet6 fe80::80e9:ddff:fe3d:681f/64 scope link proto kernel_ll 
       valid_lft forever preferred_lft forever

Switch back to dhcp

% ./run ubuntu --start-address 192.168.200.1 --end-address 192.168.200.127 --subnet-mask 255.255.255.0 
[   0.041] INFO Starting vmnet-helper for 'ubuntu' with interface id '6bbc6ce9-5e26-4b39-bc9c-28c88776d519'
[   0.148] INFO Starting 'vfkit' virtual machine 'ubuntu' with mac address '82:e9:dd:3d:68:1f'
[   4.646] INFO VM is ready at ubuntu-vmnet-helper.local

We did not detect the change (ip-address change to None), and did not generate the ciabatta.iso.

% ssh ubuntu -- ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host noprefixroute 
       valid_lft forever preferred_lft forever
2: enp0s1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 82:e9:dd:3d:68:1f brd ff:ff:ff:ff:ff:ff
    altname enx82e9dd3d681f
    inet 192.168.200.128/24 brd 192.168.200.255 scope global enp0s1
       valid_lft forever preferred_lft forever
    inet6 fdd3:28eb:866d:8319:80e9:ddff:fe3d:681f/64 scope global dynamic mngtmpaddr noprefixroute 
       valid_lft 2591992sec preferred_lft 604792sec
    inet6 fe80::80e9:ddff:fe3d:681f/64 scope link proto kernel_ll 
       valid_lft forever preferred_lft forever

So we got the same IP address in the guest.

We need to generate the network config, read the previous one, and compare. If network-config changed, we to regenerate the iso. The same way will work or user-data later if we want to change packages or mDNS implementation.

Switch back to dhcp by deleting the iso

% rm ~/.vmnet-helper/vms/ubuntu/cidata.iso 

% ./run ubuntu --start-address 192.168.200.1 --end-address 192.168.200.127 --subnet-mask 255.255.255.0
[   0.041] INFO Starting vmnet-helper for 'ubuntu' with interface id '6bbc6ce9-5e26-4b39-bc9c-28c88776d519'
[   0.166] INFO Creating cloud-init iso '/Users/nir/.vmnet-helper/vms/ubuntu/cidata.iso'
[   0.178] INFO Starting 'vfkit' virtual machine 'ubuntu' with mac address '82:e9:dd:3d:68:1f'
[   5.083] INFO VM is ready at ubuntu-vmnet-helper.local

% ssh ubuntu -- ip a                     
Warning: Permanently added 'ubuntu-vmnet-helper.local' (ED25519) to the list of known hosts.
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host noprefixroute 
       valid_lft forever preferred_lft forever
2: enp0s1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 82:e9:dd:3d:68:1f brd ff:ff:ff:ff:ff:ff
    altname enx82e9dd3d681f
    inet 192.168.200.2/24 metric 100 brd 192.168.200.255 scope global dynamic enp0s1
       valid_lft 576sec preferred_lft 576sec
    inet6 fdd3:28eb:866d:8319:80e9:ddff:fe3d:681f/64 scope global dynamic mngtmpaddr noprefixroute 
       valid_lft 2591993sec preferred_lft 604793sec
    inet6 fe80::80e9:ddff:fe3d:681f/64 scope link proto kernel_ll 
       valid_lft forever preferred_lft forever

nirs

Nice! see comment on how to fix the cidata.iso in a more generic way. I think it will be best to fix it separate from this PR.

nirs · 2026-07-14T19:36:45Z

@tofugarden we can finish this now, will be much simpler after rebase.

tofugarden · 2026-07-14T21:45:02Z

@nirs would you consider #264 first? That will also narrow down the documentation changes.

nirs · 2026-07-15T16:21:29Z

@nirs would you consider #264 first? That will also narrow down the documentation changes.

Merged now

nirs

Looks good, added some comments and questions.

nirs

Added a comment on unneeded import. Did not have time to review and test the latest version yet. I hope to do this this weekend.

nirs

Interesting that vment does not enforce that ip address is not the network address or broadcast address. I could start and access a vm with both:

% ./run server --start-address 192.168.200.1 --end-address 192.168.200.128 --subnet-mask 255.255.255.0 --ip-address 192.168.200.0 
[   0.066] INFO Starting vmnet-helper for 'server' with interface id 'bdc7b3e0-8594-4814-aa25-05187ad2a36e'
[   0.204] INFO Creating cloud-init iso '/Users/nir/.vmnet-helper/vms/server/cidata.iso'
[   0.216] INFO Starting 'vfkit' virtual machine 'server' with mac address '92:c9:52:b7:6c:08'
[   6.526] INFO VM is ready at server-vmnet-helper.local

% ssh server -- ip a                     
Warning: Permanently added 'server-vmnet-helper.local' (ED25519) to the list of known hosts.
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host noprefixroute 
       valid_lft forever preferred_lft forever
2: enp0s1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 92:c9:52:b7:6c:08 brd ff:ff:ff:ff:ff:ff
    altname enx92c952b76c08
    inet 192.168.200.0/24 brd 192.168.200.255 scope global enp0s1
       valid_lft forever preferred_lft forever
    inet6 fdd3:28eb:866d:8319:90c9:52ff:feb7:6c08/64 scope global dynamic mngtmpaddr noprefixroute 
       valid_lft 2591976sec preferred_lft 604776sec
    inet6 fe80::90c9:52ff:feb7:6c08/64 scope link proto kernel_ll 
       valid_lft forever preferred_lft forever

% ./run server --start-address 192.168.200.1 --end-address 192.168.200.128 --subnet-mask 255.255.255.0 --ip-address 192.168.200.255
[   0.069] INFO Starting vmnet-helper for 'server' with interface id 'bdc7b3e0-8594-4814-aa25-05187ad2a36e'
[   0.219] INFO Creating cloud-init iso '/Users/nir/.vmnet-helper/vms/server/cidata.iso'
[   0.234] INFO Starting 'vfkit' virtual machine 'server' with mac address '92:c9:52:b7:6c:08'
[   7.108] INFO VM is ready at server-vmnet-helper.local

% ssh server -- ip a                     
Warning: Permanently added 'server-vmnet-helper.local' (ED25519) to the list of known hosts.
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host noprefixroute 
       valid_lft forever preferred_lft forever
2: enp0s1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 92:c9:52:b7:6c:08 brd ff:ff:ff:ff:ff:ff
    altname enx92c952b76c08
    inet 192.168.200.255/24 brd 192.168.200.255 scope global enp0s1
       valid_lft forever preferred_lft forever
    inet6 fdd3:28eb:866d:8319:90c9:52ff:feb7:6c08/64 scope global dynamic mngtmpaddr noprefixroute 
       valid_lft 2591991sec preferred_lft 604791sec
    inet6 fe80::90c9:52ff:feb7:6c08/64 scope link proto kernel_ll 
       valid_lft forever preferred_lft forever

Since vmnet does not enforce this we are good.

nirs

Surprisingly this works:

% ./run server --start-address 192.168.200.130 --end-address 192.168.200.131 --subnet-mask 255.255.255.252 --ip-address 192.168.200.129
[   0.058] INFO Starting vmnet-helper for 'server' with interface id 'bdc7b3e0-8594-4814-aa25-05187ad2a36e'
[   0.177] INFO Creating cloud-init iso '/Users/nir/.vmnet-helper/vms/server/cidata.iso'
[   0.189] INFO Starting 'vfkit' virtual machine 'server' with mac address '92:c9:52:b7:6c:08'
[   7.532] INFO VM is ready at server-vmnet-helper.local

% ssh server -- ip a                     
Warning: Permanently added 'server-vmnet-helper.local' (ED25519) to the list of known hosts.
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host noprefixroute 
       valid_lft forever preferred_lft forever
2: enp0s1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 92:c9:52:b7:6c:08 brd ff:ff:ff:ff:ff:ff
    altname enx92c952b76c08
    inet 192.168.200.129/30 brd 192.168.200.131 scope global enp0s1
       valid_lft forever preferred_lft forever
    inet6 fd73:42db:f3c7:cfb3:90c9:52ff:feb7:6c08/64 scope global dynamic mngtmpaddr noprefixroute 
       valid_lft 2591992sec preferred_lft 604792sec
    inet6 fe80::90c9:52ff:feb7:6c08/64 scope link proto kernel_ll 
       valid_lft forever preferred_lft forever

% ifconfig bridge100
bridge100: flags=8a63<UP,BROADCAST,SMART,RUNNING,ALLMULTI,SIMPLEX,MULTICAST> mtu 1500
	options=3<RXCSUM,TXCSUM>
	ether 5e:e9:1e:67:7a:64
	inet 192.168.200.130 netmask 0xfffffffc broadcast 192.168.200.131
	inet6 fe80::5ce9:1eff:fe67:7a64%bridge100 prefixlen 64 scopeid 0x1b 
	inet6 fd73:42db:f3c7:cfb3:106c:ab15:162d:a768 prefixlen 64 autoconf secured 
	Configuration:
		id 0:0:0:0:0:0 priority 0 hellotime 0 fwddelay 0
		maxage 0 holdcnt 0 proto stp maxaddr 100 timeout 1200
		root id 0:0:0:0:0:0 priority 0 ifcost 0 port 0
		ipfilter disabled flags 0x0
	member: vmenet0 flags=3<LEARNING,DISCOVER>
	        ifmaxaddr 0 port 26 priority 0 path cost 0
	Address cache:
		92:c9:52:b7:6c:8 Vlan1 vmenet0 1197 flags=0<>
	nd6 options=201<PERFORMNUD,DAD>
	media: autoselect
	status: active

And it matches the docs in vmnet.h:

% cat /Library/Developer/CommandLineTools/SDKs/MacOSX26.5.sdk/System/Library/Frameworks/vmnet.framework/Versions/A/Headers/vmnet.h
...
/*!
 * @constant vmnet_start_address_key
 *
 * @abstract
 * The starting IPv4 address (string) to use for the interface.
 *
 * @discussion
 * This address is used as the gateway address. The subsequent
 * address up to and including vmnet_end_address_key are placed
 * in the DHCP pool. All other addresses are available for static
 * assignment.
 *
 * The address must be in the private IP range (RFC 1918).
 *
 * Must be specified along with vmnet_end_address_key and vmnet_subnet_mask_key.
 *
 * May be present in the interface_desc and interface_param dictionaries.
 */
...

So the validation is correct.

Allows assigning a static IP address to a VM. Move argument validation to testing/validate.py.

nirs

Thanks!

nirs requested changes Jul 4, 2026

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tofugarden force-pushed the run/static-ip branch 3 times, most recently from 4688d38 to 1fa37ea Compare July 8, 2026 14:56

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tofugarden mentioned this pull request Jul 8, 2026

run fails to discover guests via mDNS when created in host mode #259

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tofugarden force-pushed the run/static-ip branch from 1fa37ea to df06709 Compare July 15, 2026 17:07

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tofugarden force-pushed the run/static-ip branch from df06709 to 7f88b40 Compare July 19, 2026 20:40

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run: add --ip-address option

8674d2b

Allows assigning a static IP address to a VM. Move argument validation to testing/validate.py.

tofugarden force-pushed the run/static-ip branch from 7f88b40 to 8674d2b Compare July 29, 2026 16:46

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Comment thread testing/cidata.py

Comment thread testing/cidata.py

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Comment thread testing/validate.py

nirs merged commit 4964378 into nirs:main Jul 29, 2026
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Objective

Implementation notes

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Switch from dhcp to ip address

Switch back to dhcp

Switch back to dhcp by deleting the iso

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nirs commented Jul 14, 2026

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tofugarden commented Jul 3, 2026 •

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