knot: add support for ECS EDNS option

Adds a server configuration option for enabling EDNS Client Subnet. If enabled, all responses to queries containing ECS contain ECS themselves.

Just a note that the spec says server must NOT send ECS back if it's not supported (used) by the server.

Maybe this should be part of geoip module. IIRC it used to be like that.

If the configuration option is enabled, the server supports ECS even though it does not necessarily use it to create responses. This is okay with RFC 7871 which states that "when a query containing an ECS option is received, an Authoritative Nameserver supporting ECS MAY use the address information specified in the option to generate a tailored response". Sure, it does not make much sense to enable it if no module makes use of it, so the user will probably enable it only together with the geoip module or perhaps other features which might make use of ECS in the future.

You are right. I thought there was some case in ECS support probing where this was relevant but there is not.

The MR looks good to me btw.

added 1 commit

• 81004fcb - knot: add support for ECS EDNS option

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enabled an automatic merge when the pipeline for 81004fcb succeeds

merged

mentioned in commit 6ac2bad0