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RIOT-OS
gnrc_ipv6_nib/SLAAC: rfc7217 stable privacy addresses
Contribution description
Implementation of RFC7217 ("stable privacy") means that for addresses generated by SLAAC, their IID (interface identifier) is
- semantically opaque, i.e. cannot derive hwaddr from it
- random but with such parameters that it is stable within a subnet (i.e. for the same prefix on the same interface)
- derived from a randomly generated key (secret_key) that shouldn't be shared across devices. RIOT-specific: The implementation in this PR compiles the secret_key into the elffile, therefore the same elffile shouldn't be flashed onto multiple devices - in order to fulfill the RFC requirements.
Notes about implementation:
- uses tail recursion (i.e. optimizable by compiler, or manually replacable by a loop) (affects stack size)
RFC compatibility: Requirement levels: (implemented: MUST, SHOULD. not implemented: MAY, OPTIONAL.)
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Adaptability
Supports any link layer that has a hardware address: https://github.com/xnumad/RIOT/blob/88363f3cde7175691fe27399d73a54e08934e6c7/sys/net/gnrc/network_layer/ipv6/nib/_nib-slaac.c#L168-L169
The usage of IIDs which do not match the link layer address causes LOWPAN_IPHC to not be able to statelessly compress the IP address anymore. An optimization to enable compression again could be to add compression contexts (feature branch for opportunistic compression contexts: https://github.com/xnumad/RIOT/tree/feature%2Fopportunistic-compression-contexts).
6LoWPAN specifics
They do not affect this PRs current functionality but are worth noting.
For link-local addresses on a 6LN iface, this PR does not use the IDGEN (interface identifier generation) mechanism described by rfc7217.
- This is because of incompatibility with 6LoWPAN-ND (RFC6775) (and RFC8505, which would allow it, is not implemented).
- → Not fulfilling RFC7217 requirement "MUST be employed for [...] link-local"
Testing procedure
Add CFLAGS += -DCONFIG_GNRC_IPV6_STABLE_PRIVACY=1 at the appropriate position in the Makefile of examples/gnrc_networking. Tested on BOARD=nrf52840dk
Output of ifconfig command shows that SLAAC addresses have random differing IIDs (except for link-local address on a 6LoWPAN iface, see above). The IID is stable within a subnet, i.e. it also persists across reboots.
Issues/PRs references
Commits marked with 🍒 (cherry-picked) are largely derived from the RFC8981 implementation at #20369
