[riot-notifications] [RIOT-OS/RIOT] gnrc_ipv6_nib: handle route information option (#16568)

Martine Lenders notifications at github.com
Mon Jun 28 15:49:39 CEST 2021

@miri64 commented on this pull request.

> +    if (final) {
+        ext_opts = _build_final_ext_opts(netif);
+    } else {

> I think [this comment](https://github.com/RIOT-OS/RIOT/pull/16568#discussion_r659545433) still applies.

None of the items of that comment are tied to any options. The default route comes from the router advertisement itself and sending router solicitations is basically the opposite of sending router advertisements.

> We certainly wouldn't want to add the ABR option when advertising to the upstream network.

If that happens, we certainly have a bug anyways. The ABR option should only go out the 6LoWPAN border router (read downstream) interface.

> None of the options in `_build_ext_opts` make sense when sending a RA upstream - we just got them from there, no need to echo them back.

Except that adding an exception to the rule adds costly memory. It's not like the packet size for the upstream route needs to be kept small either, it is most of the time some Ethernet/Wifi link. Finally, it just smells like a bad or at least arbitrary design decision. Why does only the RIO get this `only` option? Why is there no way to send a RIO with the other options? Someone reading this code later down the line will ask these questions and also why this decisions were made. Since you are touching very central IPv6 code and going "of spec" here, your answer should be very concise and well reasoned.

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