nib.c: add interface selection rules for static link local address assignment

[DanielLockau-MLPA]

UPDATED ON: 2024-08-14, 2024-08-15

Contribution description

Setting static link local addresses is supported in nib.c.
This contribution adds options for applying static link local addresses only on specific interfaces.
Setting the static link local address can be selected by either netdev driver type or by interface number.

Testing procedure

Compile examples/gnrc_networking for board native, uncommenting the Makefile lines

IPV6_STATIC_LLADDR ?= '"fe80::cafe:cafe:cafe:1"'
CFLAGS += -DCONFIG_GNRC_IPV6_STATIC_LLADDR=$(IPV6_STATIC_LLADDR)

A static link local address will show up in ifconfig:

Iface  6  HWaddr: 56:CB:2C:67:4D:F3
          ...
          inet6 addr: fe80::cafe:cafe:cafe:7  scope: link  VAL
          ...

You can now play with the include options. Either

CFLAGS += -DCONFIG_GNRC_IPV6_STATIC_LLADDR_NETDEV_MASK="(1ULL << NETDEV_TAP)"

or

CFLAGS += -DCONFIG_GNRC_IPV6_STATIC_LLADDR_NETDEV_MASK="(1ULL << NETDEV_ANY)"

should leave the netif configuration unaltered, with the static link local address still showing up.

Other values for any of the config variable should make the link local address disappear.

Issues/PRs references

None.

[benpicco]

Maybe it's just me, but this inverse logic always leads to mental contortions.
Why not make it CONFIG_GNRC_IPV6_STATIC_LLADDR_NETDEV_MASK so the mask only tells which netdevs it applies to.

If it's not set, the static address would still apply on all interfaces.

[fabian18]

+1 for CONFIG_GNRC_IPV6_STATIC_LLADDR_NETDEV_MASK to stay compatible with the current implementation and in favor of less confusion, compared to CONFIG_GNRC_IPV6_STATIC_LLADDR_EXCLUDE_IFACE_MASK.

Was it really intended back then, to have a static address for all interfaces?
The most flexible solution IMO is to map netdev ID and index to a static address.
It takes probably more ROM to configure this but everyone would probably know what to expect from it.
... maybe as an alternative for CONFIG_GNRC_IPV6_STATIC_LLADDR.

But to solve the issue, a quick CONFIG_GNRC_IPV6_STATIC_LLADDR_NETDEV_MASK would probably be better.

[benpicco]

The most flexible solution IMO is to map netdev ID and index to a static address.

The problem with this approach is that netdev IDs are not stable and will shift around as modules (threads) get added, so using netdev IDs is always very brittle.

What works better is netdev type + index, but that's a bit more complicated code/configuration wise, so using the same link-local address for all interfaces was simply the easiest solution.

[DanielLockau-MLPA]

@benpicco @fabian18 Should I drop the second variant of selecting by interface ID altogether or also make it a positive selector?

[DanielLockau-MLPA]

@benpicco I just updated this PR with a positive selection.

[fabian18]

@benpicco @fabian18 Should I drop the second variant of selecting by interface ID altogether or also make it a positive selector?

I would not miss it. It is a potential foot gun, if for example in an application you disable one kind of interfaces but don't change this configuration and after that another interface unexpectedly has that address or the PID no longer exists.

[fabian18]

Looks good from my perspective.

[benpicco]

Please squash!

[DanielLockau-MLPA]

Please squash!

done

[riot-ci]

Murdock results

✔️ PASSED

7240d37 nib.c: allow selection of interfaces for static link local addresses

Success	Failures	Total	Runtime
10179	0	10180	14m:16s

Artifacts

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