DHCP - Why is having a DUID causing dhclient to fail?

My computer's DHCP client fails during boot. If it doesn't fail, it takes an unreasonable amount of time to acquire an IP. The main symptom is that this shows up during boot: A start job is running for Raise network interfaces [34s / 5m] In my efforts to debug it, I narrowed it down to this specific command during boot-time ifup: sudo /sbin/dhclient -4 -v -i -pf /run/dhclient.br0.pid -lf /var/lib/dhcp/dhclient.br0.leases -I -df /var/lib/dhcp/dhclient6.br0.leases br0 After a minute or so, it fails with No DHCPOFFERS received. Ultimately, removing the -i parameter solves the issue and an IP is assigned near instantly. Note that this isn't because of the bridge; it also happens with normal interfaces. According to isc-dhcp-client's man page for the -i parameter: > Use a DUID with DHCPv4 clients. If no DUID is available in the lease file one will be constructed and saved. The DUID will be used to construct a RFC4361 style client id that will be included in the client's messages. This client id can be overridden by setting a client id in the configuration file. Overridding the client id in this fashion is discouraged. ---------- **Question: Why would -i cause dhclient to fail?**