DHCPv4 NAK causes type "host" addresses to be deleted

[ColinMcInnes]

dhcpcd 10.2.0

tl;dr on NAK, with noipv4ll and persistent configured, dynamic address is deleted as expected, but so are non-dynamic addresses on same interface.

• set noipv4ll and persistent in conf
• Start dhcpcd in managed mode on eth0
• Trigger dhcpcd to start requesting addresses from DHCP server
• Configure eth0 with 2 IPv4 "host" type addresses (different from LL), these route to local host only.
• Change IP in lease on DHCP server
• Wait for renewal timer
• Expect NAK (yep!)
• dhcpcd deletes host type addresses (no!)
  -- verified via ip -4 address show dev eth0

Ideally if noipv4ll we would skip IPV4LL logic altogether, and if persistent, we would avoid touching "host" and "local" scope addresses (in linux).

~$ ip -4 address show dev eth0 
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    inet 169.254.0.2/24 scope host eth0:label0
       valid_lft forever preferred_lft forever
    inet 169.254.1.2/24 scope host eth0:label1
       valid_lft forever preferred_lft forever
    inet 192.168.229.119/24 brd 192.168.229.255 scope global dynamic noprefixroute eth0
       valid_lft 574sec preferred_lft 499sec

eth0: leased 192.168.229.119 for 600 seconds
eth0: renew in 300 seconds, rebind in 525 seconds
eth0: writing lease: /var/lib/dhcpcd/eth0.lease
eth0: adding IP address 192.168.229.119/24 broadcast 192.168.229.255
eth0: executing: /usr/libexec/dhcpcd-run-hooks RENEW
eth0: renewing lease of 192.168.229.119
eth0: sending REQUEST (xid 0xe25e7a94), next in 4.7 seconds
eth0: sending REQUEST (xid 0xe25e7a94), next in 8.4 seconds
eth0: sending REQUEST (xid 0xe25e7a94), next in 16.0 seconds
eth0: sending REQUEST (xid 0xe25e7a94), next in 31.0 seconds
eth0: sending REQUEST (xid 0xe25e7a94), next in 64.8 seconds
eth0: sending REQUEST (xid 0xe25e7a94), next in 64.5 seconds
eth0: sending REQUEST (xid 0xe25e7a94), next in 63.1 seconds
eth0: failed to renew DHCP, rebinding
eth0: spawned BPF BOOTP on PID 23837
eth0: expire in 75 seconds
eth0: sending REQUEST (xid 0xe25e7a94), next in 3.3 seconds
eth0: NAK: requested address is incorrect from 192.168.228.21
eth0: message: requested address is incorrect
eth0: deleting IP address 192.168.229.119/24
eth0: deleting route to 192.168.229.0/24
eth0: deleting default route via 192.168.229.2
eth0: executing: /usr/libexec/dhcpcd-run-hooks NAK
eth0: BPF ARP 192.168.229.119 exited from PID 4344
eth0: soliciting a DHCP lease
eth0: spawned BPF BOOTP on PID 23889
eth0: sending DISCOVER (xid 0x42b56209), next in 4.8 seconds
eth0: BPF BOOTP exited from PID 23837
eth0: offered 192.168.229.120 from 192.168.228.21
eth0: sending REQUEST (xid 0x42b56209), next in 4.3 seconds
eth0: process BPF BOOTP already started on pid 23889
eth0: acknowledged 192.168.229.120 from 192.168.228.21
eth0: spawned BPF ARP 192.168.229.120 on PID 23956
eth0: probing address 192.168.229.120/24
eth0: probing for 192.168.229.120
eth0: ARP probing 192.168.229.120 (1 of 3), next in 1.3 seconds
eth0: ARP probing 192.168.229.120 (2 of 3), next in 1.5 seconds
eth0: ARP probing 192.168.229.120 (3 of 3), next in 2.0 seconds
eth0: DAD completed for 192.168.229.120
eth0: leased 192.168.229.120 for 600 seconds
eth0: renew in 300 seconds, rebind in 525 seconds
eth0: writing lease: /var/lib/dhcpcd/eth0.lease
eth0: adding IP address 192.168.229.120/24 broadcast 192.168.229.255
eth0: ARP announcing 192.168.229.120 (1 of 2), next in 2.0 seconds
eth0: adding route to 192.168.229.0/24
eth0: adding default route via 192.168.229.2
eth0: executing: /usr/libexec/dhcpcd-run-hooks BOUND
eth0: deleting IP address 169.254.0.2/24
eth0: deleting IP address 169.254.1.2/24
eth0: executing: /usr/libexec/dhcpcd-run-hooks IPV4LL
eth0: BPF BOOTP exited from PID 23889
eth0: ARP announcing 192.168.229.120 (2 of 2)
eth0: renewing lease of 192.168.229.120
eth0: sending REQUEST (xid 0xc2801c9), next in 3.1 seconds
eth0: acknowledged 192.168.229.120 from 192.168.228.21
eth0: leased 192.168.229.120 for 600 seconds
eth0: renew in 300 seconds, rebind in 525 seconds
eth0: writing lease: /var/lib/dhcpcd/eth0.lease
eth0: adding IP address 192.168.229.120/24 broadcast 192.168.229.255
eth0: executing: /usr/libexec/dhcpcd-run-hooks RENEW

~$ ip -4 address show dev eth0 
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    inet 192.168.229.120/24 brd 192.168.229.255 scope global dynamic noprefixroute eth0
       valid_lft 333sec preferred_lft 258sec

[ColinMcInnes]

Reviewing the code, I think the underlying issue could be resolved if I used an actual "localhost" address instead.

dhcpcd is comparing the address to the "link local" range to determine that it's a link local address.

That would be the quick solution. Ideally IN_LINKLOCAL could also verify in linux if the address is "scope local".

I'm still looking into why it's triggering IPv4LL functions when noipv4ll was set. ipv4ll_drop also checks for persistent...