hostapd fails with "Invalid ipaddr_type_availability" when configured for IPv6 only

[Russell Phillips]

I'm running an IPv6-only WLAN (a typical NAT64/DNS64 setup) and I believe I'm having my config rejected erroneously when attempting to advertise a total lack of IPv4 networking.

In /etc/hostapd/hostapd.conf, I have ipaddr_type_availability set to "1", to signify that IPv4 is not availabile, but IPv6 is:

# IP Address Type Availability
# format: <1-octet encoded value as hex str>
# (ipv4_type & 0x3f) << 2 | (ipv6_type & 0x3)
# ipv4_type:
# 0 = Address type not available
# 1 = Public IPv4 address available
# 2 = Port-restricted IPv4 address available
# 3 = Single NATed private IPv4 address available
# 4 = Double NATed private IPv4 address available
# 5 = Port-restricted IPv4 address and single NATed IPv4 address available
# 6 = Port-restricted IPv4 address and double NATed IPv4 address available
# 7 = Availability of the address type is not known
# ipv6_type:
# 0 = Address type not available
# 1 = Address type available
# 2 = Availability of the address type not known
ipaddr_type_availability=1

When I attempt to start hostapd, I get the following error:

# hostapd -d /etc/hostapd/hostapd.conf
random: Trying to read entropy from /dev/random
Configuration file: /etc/hostapd/hostapd.conf
Line 13: Invalid ipaddr_type_availability '1'
1 errors found in configuration file '/etc/hostapd/hostapd.conf'
Failed to set up interface with /etc/hostapd/hostapd.conf
hostapd_init: free iface 0x55fd5f7c0710
Failed to initialize interface

If I set ipaddr_type_availability to "1D" (unknown IPv4/IPv6 available), hostapd will run without issue - but it's advertising that the IPv4 availability is unknown, which isn't quite what I was looking for.

I believe this is a bug because the documentation suggests that having no IPv4 availability is a valid configuration.

[Russell Phillips (ignissport)]

A month later, I just realised this works:

ipaddr_type_availability=01

It needs to be zero-padded to 2 digits to work. Go figure.