IP addresses use CIDR notation, gateways are optional but need an IP of the same type specified.
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The special string 'dhcp' can be used for IP addresses to use DHCP, in which case no explicit gateway should be provided.
+For IPv6 the special string 'auto' can be used to use stateless autoconfiguration.
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If cloud-init is enabled and neither an IPv4 nor an IPv6 address is specified, it defaults to using dhcp on IPv4.