dhcpcd-discuss

I'm running Raspbian on the Raspberry Pi and have been encountering DHCP
issues with my USB 3G modem.

The previous discussion for this issue is here
https://github.com/raspberrypi/linux/issues/2544, but to summarise, dhcpcd
6.10.1 works as expected, but dhcpcd 6.11.5 does not.

The modem driver (sierra_net) exposes a wwan0 interface, and on dhcpcd
6.10.1, the interface successfully gets the IPv4 address and the interface
works as expected.

Using dhcpcd 6.11.5, the wwan0 interface does not get an IP address, so I
can't use it. If I downgrade back to 6.10.1, then the interface gets the IP
address and starts working again.

Here is the syslog snippet using 6.10.1 (good)

Sep  7 15:54:40 raspberrypi dhcpcd[250]: wwan0: waiting for carrier
Sep  7 15:54:40 raspberrypi kernel: [   21.042350] IPv6:
ADDRCONF(NETDEV_UP): wwan0: link is not ready
Sep  7 15:54:41 raspberrypi systemd[1]: Started Raise network interfaces.
Sep  7 15:54:42 raspberrypi kernel: [   22.660424] IPv6:
ADDRCONF(NETDEV_CHANGE): wwan0: link becomes ready
Sep  7 15:54:42 raspberrypi dhcpcd[250]: wwan0: carrier acquired
Sep  7 15:54:42 raspberrypi dhcpcd[250]: wwan0: adding address
fe80::1e09:995:5f42:fa48
Sep  7 15:54:43 raspberrypi dhcpcd[250]: DUID
00:01:00:01:21:44:28:43:26:46:ee:43:01:07
Sep  7 15:54:43 raspberrypi dhcpcd[250]: wwan0: IAID ee:43:01:07
Sep  7 15:54:43 raspberrypi dhcpcd[250]: wwan0: soliciting a DHCP lease
Sep  7 15:54:43 raspberrypi dhcpcd[250]: wwan0: soliciting an IPv6 router
Sep  7 15:54:43 raspberrypi dhcpcd[250]: wwan0: offered 100.113.23.172
from 100.113.23.253
Sep  7 15:54:43 raspberrypi dhcpcd[250]: wwan0: probing address
100.113.23.172/32

and the same for 6.11.5 (bad):

Nov 29 02:37:27 raspberrypi dhcpcd[238]: wwan0: waiting for carrier
Nov 29 02:37:27 raspberrypi dhcpcd[238]: wwan0: carrier acquired
Nov 29 02:37:27 raspberrypi dhcpcd[238]: wwan0: IAID 17:fa:01:07
Nov 29 02:37:27 raspberrypi dhcpcd[238]: wwan0: adding address
fe80::3cc3:cfbd:f6e4:82ec
Nov 29 02:37:27 raspberrypi dhcpcd[238]: wwan0: carrier lost
Nov 29 02:37:27 raspberrypi dhcpcd[238]: wwan0: deleting address
fe80::3cc3:cfbd:f6e4:82ec


Can anyone help me to figure out why 6.11.5 isn't working as expected, and
if there is a configuration I can change to resolve the issue?


Regards,

Jeremy