Configuring DHCP options? Generating bootpd.plist on Mac?

[nickpapadonis]

Is it possible to configure DHCP options, placed in /etc/bootpd.plist, through socket_vmnet? I suspect this utility may be auto generating /etc/bootpd.plist on MacOS where such options may go. Placing this here to make sure I don't reinvent something already accomplished.

It would be helpful to configure certain options like DNS server IP, DNS search, NIS info (where NFS shares are), etc.. I believe the options look like this in the Subnet section of the file:

<key>dhcp_option_66</key> <data>YOUR_BASE64_ENCODED_SERVER_NAME</data>
<key>dhcp_option_67</key> <data>YOUR_BASE64_ENCODED_BOOTFILE_NAME</data>

I have the current configuration working:
socket_vmnet --vmnet-gateway=192.168.57.1 --vmnet-dhcp-end=192.168.57.100 /var/run/socket_vmnet

/etc/bootptab

# bootptab
%%
# hostname      hwtype  hwaddr              ipaddr          bootfile
deb12-0         1       52:54:00:12:34:56   192.168.57.1

socket_vmnet_client /var/run/socket_vmnet qemu-system-x86_64  -accel hvf  -device virtio-net-pci,netdev=net0,mac=52:54:00:12:34:56 -netdev socket,id=net0,fd=3  -m 4096 -drive file=debian_12-1_s0-disk1.qcow2

So far my thoughts are this process, outside of socket_vmnet:

sudo launchctl stop bootpd
<modify /etc/bootpd.plist to include options>
sudo launchctl unload -F /System/Library/LaunchDaemons/bootps.plist
sudo launchctl load -F /System/Library/LaunchDaemons/bootps.plist

[nickpapadonis]

I found a debug work around solution to this problem. There are two solutions to running your own DHCP server so you can provide DHCP options to QEMU VMs. Here is my working debug configs. One is to use ISC DHCP server on the Mac, disabling MacOS DHCP server in scripts. The other is to use the Mac supplied DHCP server and edit some config files. It would be nice if socket_vmnet had an option to disable the DHCP server (I tried limiting the IP range to nothing, but it still assigns an IP and the Mac DHCP server starts). When I finish testing I'll put a write up of this somewhere.

USE ISC DHCP SERVER:

1. Install

sudo port install socket_vmnet
sudo port install isc-dhcp

2. Configure ISC DHCP server

3. Start ISC DHCP server

4. Launch socket_vmnet

sudo socket_vmnet --vmnet-interface=bridge100 --vmnet-gateway=192.168.57.1 --vmnet-dhcp-end=192.168.57.1 /var/run/socket_vmnet

4. Stop DHCP server on MacOS

sudo launchctl unload -F /System/Library/LaunchDaemons/bootps.plist

5. Now start the VM

socket_vmnet_client /var/run/socket_vmnet qemu-system-x86_64  -accel hvf  -device virtio-net-pci,netdev=net0,mac=52:54:00:12:34:56 -netdev socket,id=net0,fd=3 -m 8000 -drive file=debian_12-1_s0-disk1.qcow2

MAC SUPPLIED BOOTP/DHCPD:

The other option is to use the MacOS supplied DHCP server with options:

1. Install socket_vmnet
2. Configure MacOS DHCP server

cd /etc
sudo cp bootpd.plist bootpd.plist.socket_vmnet

3. Edit bootpd.plist in <subnets><array><dict> section add following:
			<!-- Debian Includes These -->
			<!-- Auto-Config -->
			<key>dhcp_option_116</key>
			<string>1</string>

			<!-- Broadcast Address -->
			<key>dhcp_option_28</key>
			<string>192.168.57.255</string>

			<!-- Time Offset in Seconds from UTC -->
			<key>dhcp_option_2</key>
			<string>-18000</string>

			<!-- Routers -->
			<key>dhcp_option_3</key>
			<array>
			<string>192.168.57.1</string>
			</array>

			<!-- DNS Domain -->
			<key>dhcp_option_15</key>
			<string>p0.mac</string>

			<!-- Domain Servers -->
			<key>dhcp_option_6</key>
			<array>
			<string>192.168.57.1</string>
			</array>

			<!-- Domain Search -->
			<key>dhcp_option_119</key>
			<string>p0.mac</string>

			<!-- DHCP6 NS, DSearch, FQDN, SNTP? -->

			<!-- Classless Static Routes -->
			<key>dhcp_option_121</key>
			<array>
			<string>192.168.57.0</string>
			<string>192.168.57.1</string>
			<string>192.168.56.0</string>
			<string>192.168.57.1</string>
			<string>10.0.2.0</string>
			<string>10.0.0.2</string>
			</array>

			<!-- NTP Servers -->
			<key>dhcp_option_42</key>
			<string>192.168.57.1</string>

			<!-- Must Edit /etc/dhcp/dhclient.conf to request -->

			<!-- IEEE 1003.1 TZ String -->
			<key>dhcp_option_100</key>
			<string>EST5EDT,M3.2.0/2,M11.1.0</string>

			<!-- Reference to TZ Database -->
			<key>dhcp_option_101</key>
			<string>America/New_York</string>

			<!-- Nameservers -->
			<key>dhcp_option_5</key>
			<string>192.168.57.1</string>

			<!-- IP Address Lease Time-->
			<key>dhcp_option_51</key>
			<string>86400</string>

			<!-- Time Servers -->
			<key>dhcp_option_4</key>
			<string>192.168.57.1</string>

			<!-- LDAP -->
			<key>dhcp_option_95</key>
			<string>192.168.57.1</string>

			<!-- NIS Domain -->
			<key>dhcp_option_40</key>
			<string>p0.mac</string>
			<!-- NIS Domain Name -->
			<key>dhcp_option_64</key>
			<string>p0.mac</string>

			<!-- NIS Servers-->
			<key>dhcp_option_41</key>
			<string>192.168.57.1</string>
			<!-- NIS Server Addr -->
			<key>dhcp_option_65</key>
			<string>192.168.57.1</string>

At the bottom change:

<key>use_server_config_for_dhcp_options</key>
<false/>

5. Edit /etc/bootptab

$ sudo cat bootptab    
# bootptab
%%
# hostname      hwtype  hwaddr              ipaddr          bootfile
deb12-0         1       52:54:00:12:34:56   192.168.57.2

5. Start socket_vmnet per ISC config above

6. Stop the MacOS DHCP server

sudo cp bootpd.plist.socket_vmnet bootpd.plist && sudo launchctl unload -F /System/Library/LaunchDaemons/bootps.plist && sudo launchctl load -F /System/Library/LaunchDaemons/bootps.plist

7. Launch the VM via QEMU per above ISC config steps

If you're going to do NAT over the same interface you need something like this. Edit /etc/pf.conf

#
# com.apple anchor point
#
icmp_types = "echoreq"
#priv_nets = "{ 127.0.0.0/8, 192.168.57.0/24, 10.0.0.0/8 }";

set block-policy drop
set loginterface en1
set skip on lo0

scrub in all

scrub-anchor "com.apple/*"
nat-anchor "com.apple/*"
rdr-anchor "com.apple/*"


nat on en1 from bridge100:network to any -> (en1)
pass in quick on bridge100 inet from 192.168.0.0/24 to 192.168.0.10

pass out quick on en1 proto udp all keep state
pass out quick on en1 proto tcp all modulate state flags S/SA

pass in quick on bridge100 inet from 192.168.0.0/24 to 192.168.57.1
pass in quick on bridge100 inet from 192.168.0.0/24 to any keep state

pass in quick log on 192.168.57.1 all
pass in all
pass out all


dummynet-anchor "com.apple/*"
anchor "com.apple/*"
load anchor "com.apple" from "/etc/pf.anchors/com.apple"

$ sudo pfctl -n -f /etc/pf.conf

[nickpapadonis]

I'll leave this open for now. Hoping for a comment from maintainers if DHCP server can be disabled at invocation, or perhaps that's some part of Apple Code that creates bridge100.

[AkihiroSuda]

if DHCP server can be disabled at invocation

macOS 26 will have the API for that

https://developer.apple.com/documentation/vmnet/vmnet_network_configuration_disable_dhcp(_:)?language=objc

[nickpapadonis]

Thanks. It appears this type of workaround resolves the issue until that OS release.