Odd behaviour with AutoIP and Static IP #68238

GeorgeAtKistler · 2024-01-29T16:20:16Z

GeorgeAtKistler
Jan 29, 2024

Hi all

On my device, I would like to be able to switch between a static IP and DHCP. In case there is no DHCP response, AutoIP should be used.
First of all, I would want to have only one single network interface. But when AutoIP is enabled, the number of interfaces gets automatically set to 2, see https://docs.zephyrproject.org/3.4.0/kconfig.html#CONFIG_NET_IF_UNICAST_IPV4_ADDR_COUNT.
As already discussed in #27651, this seems rater odd.

I am trying to understand how this works together with setting a static IP.
My test is based on samples/net/ipv4_autoconf but I replaced src/main.c with the attached main.c.

*** Booting Zephyr OS build zephyr-v3.4.0 ***
[00:00:00.001,000] <inf> net_ipv4_autoconf_sample: Run ipv4 autoconf client with static IP
[00:00:00.001,000] <wrn> net_ipv4_autoconf_sample: Startup:
[00:00:00.001,000] <inf> net_ipv4_autoconf_sample: Slot: 1 of 2
[00:00:00.001,000] <inf> net_ipv4_autoconf_sample:   Your address: 79.110.214.51
[00:00:00.001,000] <inf> net_ipv4_autoconf_sample:   Subnet:       44.194.72.198
[00:00:00.001,000] <inf> net_ipv4_autoconf_sample:   Type: static
[00:00:00.001,000] <inf> net_ipv4_autoconf_sample: Slot: 2 of 2
[00:00:00.001,000] <inf> net_ipv4_autoconf_sample:   Your address: 19.148.87.2
[00:00:00.001,000] <inf> net_ipv4_autoconf_sample:   Subnet:       44.194.72.198
[00:00:00.001,000] <inf> net_ipv4_autoconf_sample:   Type: static

-> Both slots seem to have odd addresses and net masks. Maybe this is simply the default?

-> Next I set a static IP (address=192.168.2.100 and mask=255.255.255.0).
Note that I have to use net_if_ipv4_addr_add() since there is no API net_if_ipv4_addr_add_by_index(), so I can't select the slot.

[00:00:00.001,000] <wrn> net_ipv4_autoconf_sample: Configuring static IP...

Then I read out the config again:

[00:00:00.001,000] <wrn> net_ipv4_autoconf_sample: After setting the static IP:
[00:00:00.001,000] <inf> net_ipv4_autoconf_sample: Slot: 1 of 2
[00:00:00.001,000] <inf> net_ipv4_autoconf_sample:   Your address: 192.168.2.100
[00:00:00.001,000] <inf> net_ipv4_autoconf_sample:   Subnet:       255.255.255.0
[00:00:00.001,000] <inf> net_ipv4_autoconf_sample:   Type: static
[00:00:00.001,000] <inf> net_ipv4_autoconf_sample: Slot: 2 of 2
[00:00:00.001,000] <inf> net_ipv4_autoconf_sample:   Your address: 0.0.0.0
[00:00:00.001,000] <inf> net_ipv4_autoconf_sample:   Subnet:       255.255.255.0
[00:00:00.001,000] <inf> net_ipv4_autoconf_sample:   Type: static

-> Slot 1 got configured as expected. Slot 2 kind of gets disabled (0.0.0.0).

-> After a while, AutoIP kicks in and changes both slots:

[00:00:12.320,000] <wrn> net_ipv4_autoconf_sample: After net mgmt event:
[00:00:12.320,000] <inf> net_ipv4_autoconf_sample: Slot: 1 of 2
[00:00:12.320,000] <inf> net_ipv4_autoconf_sample:   Your address: 192.168.2.100
[00:00:12.320,000] <inf> net_ipv4_autoconf_sample:   Subnet:       255.255.0.0
[00:00:12.320,000] <inf> net_ipv4_autoconf_sample:   Type: static
[00:00:12.320,000] <inf> net_ipv4_autoconf_sample: Slot: 2 of 2
[00:00:12.320,000] <inf> net_ipv4_autoconf_sample:   Your address: 169.254.209.13
[00:00:12.320,000] <inf> net_ipv4_autoconf_sample:   Subnet:       255.255.0.0
[00:00:12.320,000] <inf> net_ipv4_autoconf_sample:   Type: static

-> Slot 2 now has an AutoIP which is ok. It also changed its netmask to 255.255.0.0 which seems to be the expected value on AutoIP.
-> How ever, why did the net mask of slot 1 change? This looks like a bug to me.

Answered by jukkar

Jan 29, 2024

I would want to have only one single network interface. But when AutoIP is enabled, the number of interfaces gets automatically set to 2,

It is not the network interface that get increased but the number of unicast IPv4 addresses that can be assigned to the network interface.

Both slots seem to have odd addresses and net masks. Maybe this is simply the default?

Looks like some garbage values when no address have been set yet.

Slot 2 now has an AutoIP which is ok. It also changed its netmask to 255.255.0.0 which seems to be the expected value on AutoIP.

There is currently a limitation that we can only have one netmask for the network interface. So you are basically just printing the …

View full answer

jukkar · 2024-01-29T19:22:55Z

jukkar
Jan 29, 2024
Collaborator

I would want to have only one single network interface. But when AutoIP is enabled, the number of interfaces gets automatically set to 2,

It is not the network interface that get increased but the number of unicast IPv4 addresses that can be assigned to the network interface.

Both slots seem to have odd addresses and net masks. Maybe this is simply the default?

Looks like some garbage values when no address have been set yet.

Slot 2 now has an AutoIP which is ok. It also changed its netmask to 255.255.0.0 which seems to be the expected value on AutoIP.

There is currently a limitation that we can only have one netmask for the network interface. So you are basically just printing the same value twice. We do not have proper IP routing implemented atm in zephyr, but if you have only one network interface, then things should work.

1 reply

GeorgeAtKistler Jan 31, 2024
Author

Thank you for the explanations!

Looks like some garbage values when no address have been set yet.

Is this the intended behavior or should I file a bug?
I would expect until it gets configured, it has eg. 0.0.0.0.
Or did I miss a required function call?

There is currently a limitation that we can only have one netmask for the network interface

This clearly messes the 2-slot system up and actually makes it useless!
Are there plans to fix this?
Is it even technically possible/allowed?

As for my needs, I found that setting CONFIG_NET_IF_UNICAST_IPV4_ADDR_COUNT=1 and applying the patch from #50245 provides us the expected functionality.

It is a pitty that that patch did not get accepted, eg. with a config option.

I found one further issue but this is unrelated to my changes:
After a DHCP lease expires (no new DHCPACK gets received in time), the DHCP IP must be no longer used. See https://serverfault.com/questions/1136060/dhcp-renewal-cant-go-through-because-dhcp-server-is-down. This seems not to be the case in Zephyr as it keeps the DHCP provided IP forever.

Before the lease (5 minutes) expires:

[00:02:21.513,000] <inf> netconfig_testbench: Slot: 1 of 2
[00:02:21.513,000] <inf> netconfig_testbench:   Your address: 10.10.2.235
[00:02:21.513,000] <inf> netconfig_testbench:   Subnet:    255.255.255.0
[00:02:21.513,000] <inf> netconfig_testbench:   Type: dhcp
[00:02:21.513,000] <inf> netconfig_testbench: Slot: 2 of 2
[00:02:21.513,000] <inf> netconfig_testbench:   Your address: 0.0.0.0
[00:02:21.513,000] <inf> netconfig_testbench:   Subnet:    255.255.255.0
[00:02:21.513,000] <inf> netconfig_testbench:   Type: static

> net iface

Interface 0x240016d0 (Ethernet) [1]
===================================
Link addr : 00:07:29:8E:5C:12
MTU       : 1500
Flags     : AUTO_START,IPv4,IPv6
Ethernet capabilities supported:
        10 Mbits
        100 Mbits
IPv6 unicast addresses (max 2):
        fe80::207:29ff:fe8e:5c12 autoconf preferred infinite
IPv6 multicast addresses (max 3):
        ff02::1
        ff02::1:ff8e:5c12
IPv6 prefixes (max 2):
        <none>
IPv6 hop limit           : 64
IPv6 base reachable time : 30000
IPv6 reachable time      : 22571
IPv6 retransmit timer    : 0
IPv4 unicast addresses (max 2):
        10.10.2.235 DHCP preferred
IPv4 multicast addresses (max 1):
        239.253.253.239
IPv4 gateway : 0.0.0.0
IPv4 netmask : 255.255.255.0
DHCPv4 lease time : 300
DHCPv4 renew time : 150
DHCPv4 server     : 10.10.2.224
DHCPv4 requested  : 10.10.2.235
DHCPv4 state      : bound
DHCPv4 attempts   : 1

After the lease expired and did not get reneved:

[00:08:43.532,000] <inf> netconfig_testbench: Slot: 1 of 2
[00:08:43.532,000] <inf> netconfig_testbench:   Your address: 10.10.2.235
[00:08:43.532,000] <inf> netconfig_testbench:   Subnet:    255.255.255.0
[00:08:43.532,000] <inf> netconfig_testbench:   Type: dhcp
[00:08:43.532,000] <inf> netconfig_testbench: Slot: 2 of 2
[00:08:43.532,000] <inf> netconfig_testbench:   Your address: 0.0.0.0
[00:08:43.532,000] <inf> netconfig_testbench:   Subnet:    255.255.255.0
[00:08:43.532,000] <inf> netconfig_testbench:   Type: static

> net iface

Interface 0x240016d0 (Ethernet) [1]
===================================
Link addr : 00:07:29:8E:5C:12
MTU       : 1500
Flags     : AUTO_START,IPv4,IPv6
Ethernet capabilities supported:
        10 Mbits
        100 Mbits
IPv6 unicast addresses (max 2):
        fe80::207:29ff:fe8e:5c12 autoconf preferred infinite
IPv6 multicast addresses (max 3):
        ff02::1
        ff02::1:ff8e:5c12
IPv6 prefixes (max 2):
        <none>
IPv6 hop limit           : 64
IPv6 base reachable time : 30000
IPv6 reachable time      : 22571
IPv6 retransmit timer    : 0
IPv4 unicast addresses (max 2):
        <none>
IPv4 multicast addresses (max 1):
        239.253.253.239
IPv4 gateway : 0.0.0.0
IPv4 netmask : 255.255.255.0
DHCPv4 lease time : 0
DHCPv4 renew time : 0
DHCPv4 server     : 0.0.0.0
DHCPv4 requested  : 0.0.0.0
DHCPv4 state      : selecting
DHCPv4 attempts   : 9

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Odd behaviour with AutoIP and Static IP #68238

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Odd behaviour with AutoIP and Static IP #68238

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GeorgeAtKistler Jan 29, 2024

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jukkar Jan 29, 2024 Collaborator

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GeorgeAtKistler Jan 31, 2024 Author

GeorgeAtKistler
Jan 29, 2024

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jukkar
Jan 29, 2024
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GeorgeAtKistler Jan 31, 2024
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