dhcpcd-discuss

Hi,


There seems to be a problem in which a network interface is sometimes 
not get assigned an IPv6 link local address if the network interface 
goes quickly up -> down -> up again.


- dhcpcd version 7.0.8 that is shipped with Raspbian

- Raspberry Pi 3B+, to which a USB Ethernet gadget device is attached 
(Pi zero running gpioexpander image: 
https://www.raspberrypi.org/blog/gpio-expander/ )


dmesg:


==

[  204.483268] usb 1-1.3: new high-speed USB device number 10 using dwc_otg
[  204.614336] usb 1-1.3: New USB device found, idVendor=f055, 
idProduct=0001, bcdDevice= 4.04
[  204.614352] usb 1-1.3: New USB device strings: Mfr=1, Product=2, 
SerialNumber=3
[  204.614363] usb 1-1.3: Product: Pi Zero - GPIO expansion board
[  204.614373] usb 1-1.3: Manufacturer: Raspberry Pi
[  204.614382] usb 1-1.3: SerialNumber: 000000006099b31e
[  204.682662] cdc_acm 1-1.3:1.0: ttyACM0: USB ACM device
[  204.684608] usbcore: registered new interface driver cdc_acm
[  204.684623] cdc_acm: USB Abstract Control Model driver for USB modems 
and ISDN adapters
[  204.693959] cdc_ether 1-1.3:1.2 usb0: register 'cdc_ether' at 
usb-3f980000.usb-1.3, CDC Ethernet Device, fa:00:60:99:b3:1e
[  204.695436] usbcore: registered new interface driver cdc_ether
[  204.817299] IPv6: ADDRCONF(NETDEV_UP): usb0: link is not ready
[  204.846568] IPv6: ADDRCONF(NETDEV_CHANGE): usb0: link becomes ready

==


dhcpcd claims that the carrier quickly goes up -> down -> up again. It 
does assign IPv6 link local the first time link goes up, but fails to do 
so second time.


==

Oct 19 11:48:16 raspberrypi dhcpcd[395]: usb0: waiting for carrier
Oct 19 11:48:16 raspberrypi dhcpcd[395]: usb0: carrier acquired
Oct 19 11:48:16 raspberrypi dhcpcd[395]: usb0: IAID 60:99:b3:1e
Oct 19 11:48:16 raspberrypi dhcpcd[395]: usb0: adding address 
fe80::4d92:7daa:a2d7:b46
Oct 19 11:48:16 raspberrypi dhcpcd[395]: usb0: carrier lost
Oct 19 11:48:16 raspberrypi dhcpcd[395]: usb0: deleting address 
fe80::4d92:7daa:a2d7:b46
Oct 19 11:48:16 raspberrypi dhcpcd[395]: usb0: carrier acquired
Oct 19 11:48:16 raspberrypi dhcpcd[395]: usb0: IAID 60:99:b3:1e
Oct 19 11:48:16 raspberrypi dhcpcd[395]: usb0: soliciting an IPv6 router
Oct 19 11:48:16 raspberrypi dhcpcd[395]: usb0: soliciting a DHCP lease
Oct 19 11:48:21 raspberrypi dhcpcd[395]: usb0: probing for an IPv4LL address
Oct 19 11:48:26 raspberrypi dhcpcd[395]: usb0: using IPv4LL address 
169.254.140.228
Oct 19 11:48:26 raspberrypi dhcpcd[395]: usb0: adding route to 
169.254.0.0/16
==


- The problem does not occur on a Pi 4 and a Pi 1 using the same SD 
card. (interface does go up -> down -> up, but it does get an IPv6 link 
local address assigned)

And it is not 100% reproducible on a Pi 3+B either, but does happen 
often on that.

Therefore I believe the problem is timing specific

- Other reports: 
https://www.raspberrypi.org/forums/viewtopic.php?f=91&t=254541



Yours sincerely,


Floris Bos