accel-ppp.git/accel-pppd/include/ipv6_dns.h, branch 1.15.0

ipv6: remove obsolete three-server DNS limit

2026-10-05T23:19:48+00:00

The legacy limit matches RFC 6106's recommendation that hosts treat three learned RDNSS addresses as sufficient. That was host-side repository guidance, not a limit in the RADIUS, DHCPv6, or RDNSS encodings. RFC 8106 obsoletes RFC 6106 and explicitly removes the recommendation to limit learned RDNSS addresses to three, leaving the number to local policy. It instead recommends the ability to store at least three addresses when DNS information comes from multiple sources. Store both configured and per-session servers in reusable contiguous arrays. Start with a four-address, 64-byte allocation, grow geometrically, retain capacity across reload or reauthorization, and free session storage only at teardown. Bound advertised lists by actual DHCPv6 and router-advertisement packet space. Warn when servers have to be dropped for lack of room, as the fixed limit used to, skip the DNS search list rather than write it past the end of a full advertisement, and drop the stale three-server wording from the [ipv6-dns] documentation. Link: https://github.com/accel-ppp/accel-ppp/commit/4f562467dbdf819395e138617c2a057e02595b9e#r197212083 Link: https://www.rfc-editor.org/rfc/rfc6106.html#section-5.3.1 Link: https://www.rfc-editor.org/rfc/rfc8106.html#section-5.3.1 Link: https://www.rfc-editor.org/rfc/rfc8106.html#appendix-A

ipv6: use a dedicated type for per-session DNS

2026-10-05T23:18:41+00:00

DNS-Server-IPv6-Address carries a full IPv6 address, so storing it in ipv6db_addr_t also carried an unused prefix length and flags. Introduce dedicated DNS list and address types so the representation matches the data. Suggested-by: Vladislav Grishenko <566150+themiron@users.noreply.github.com> Link: https://github.com/accel-ppp/accel-ppp/commit/4f562467dbdf819395e138617c2a057e02595b9e#r197215804

ipv6: assign DNS servers per session from RADIUS

2026-08-12T07:42:35+00:00

The ipv6_nd and ipv6_dhcp modules could only advertise the DNS servers configured in [ipv6-dns], the same set for every subscriber. RFC 6911 defines DNS-Server-IPv6-Address (attribute 169) for exactly this, and the attribute was already in the shipped dictionary and in attr_defs.h; nothing read it. Give struct ap_session an ipv6_dns list, filled by the radius module from that attribute, and have both modules advertise it when the session has one: in the RDNSS option of the router advertisements, and in the DNS_SERVERS option of DHCPv6 replies. Sessions without a list of their own keep getting the configured servers, so nothing changes for anyone not sending the attribute. The selection is a single ipv6_dns_get() shared by both modules rather than a copy in each: they already duplicate the whole [ipv6-dns] parser, and two copies of a precedence rule are two chances to drift. It caps what it returns, so neither the RDNSS option length (one byte, in units of 8) nor the router advertisement buffer can be pushed around by what a RADIUS server sends. The radius module caps at the same 3 servers as [ipv6-dns] accepts and warns once when a reply carries more. An Access-Accept which carries the attribute replaces the whole previously assigned list rather than appending to it, so a re-authorized session ends up with the servers of the latest reply and not with a concatenation. One which does not carry it leaves the current list alone, which is how the IPv4 MS-Primary-DNS-Server attribute already behaves. ipv6_dns_test.c covers the selection: assigned wins over configured, empty list means "nothing assigned" rather than "no DNS", the cap holds for both sources, and a caller with no room gets nothing rather than a stomped buffer. Wired into the ASAN/UBSAN workflow. Inspired by the per-session IPv6 DNS support in accel-ppp-ng (commit 2df6eb99), reimplemented against mainline's ap_session and ipdb types.