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machines/stellio: stop deprecating a PD prefix the ISP re-delegates (sync with cnx-network 45643d6)

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The ISP modem restart at 08:19 re-delegated the same /64 five seconds
after the PPPoE drop. networkd re-announced it at once, but the fixed
7 s radvd run kept sending preferred-lifetime-0 RAs for it, so clients
sat on a deprecated prefix until networkd's next periodic RA and IPv6
stayed broken for minutes.

Send one RA per radvd start, up to three 3 s apart, and skip each one if
the /64 is already back on the interface. Verified on stellio with the
rendered script: a prefix gone for good -> three RAs; the PD address
removed and re-added 4 s later -> two RAs, then "is back, leaving it
announced", client preferred again and pinging over v6.
This commit is contained in:
kurogeek committed 2026-10-08 08:36:59 +00:00
1 parent 31ebf2d081
commit 7f3457859e
1 file changed
+29 -11
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machines/stellio/configuration.nix
+29 -11
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@@ -108,7 +108,7 @@
systemd.network.networks."40-vlan-lan".dhcpPrefixDelegationConfig.SubnetId = lib.mkForce "0x0";
systemd.network.networks."40-vlan-mgmt".dhcpPrefixDelegationConfig.SubnetId = lib.mkForce "0x1";
# Interim copy of cnx-network-clan fa11327 (router/ipv6: deprecate
# Interim copy of cnx-network-clan 45643d6 (router/ipv6: deprecate
# withdrawn DHCPv6-PD prefixes); drop when the input is bumped past it.
# networkd never deprecates a prefix it stops announcing (systemd#29651):
# on every reboot the first PPPoE session lands on another AIS BNG, is
@@ -117,10 +117,12 @@
# one preferred for the rest of its 1800 s lifetime, so RFC 6724 source
# selection picks the dead prefix and every v6 connection fails for up
# to 30 minutes (2026-10-08 07:57). Watch vlan-* for networkd removing a
# dynamic (PD) address and send a few RAs with that /64 at preferred
# lifetime 0; radvd is only the packet generator, killed hard after ~7 s
# so it sends no shutdown RA (router lifetime 0) and does not keep
# deprecating a prefix the ISP re-delegates on reconnect.
# dynamic (PD) address and send up to three RAs with that /64 at
# preferred lifetime 0, one short-lived radvd per RA (SIGKILLed: no
# shutdown RA with router lifetime 0), stopping as soon as the prefix is
# back on the interface -- a plain flap re-delegates the same /64 within
# seconds and a deprecating RA sent after networkd re-announced it would
# leave clients deprecated until the next periodic RA (08:19 today).
systemd.services.router-radv-deprecate = {
description = "Deprecate withdrawn DHCPv6-PD prefixes on the VLANs";
wantedBy = [ "multi-user.target" ];
@@ -138,11 +140,18 @@
script = ''
conf=$RUNTIME_DIRECTORY/radvd.conf
pid=$RUNTIME_DIRECTORY/radvd.pid
# /64s of the global addresses currently on an interface.
prefixes_on() {
ip -o -6 addr show dev "$1" scope global | while read -r _ _ _ a _; do
echo "$(ipcalc --no-decorate -n "$a")/''${a##*/}"
done
}
# "Deleted 4: vlan-lan inet6 2001:db8::1/64 scope global dynamic mngtmpaddr \ valid_lft ..."
ip -o -6 monitor address | while read -r event _ dev _ addr _ scope rest; do
[[ $event == Deleted && $dev == vlan-* && $scope == global && $rest == *dynamic* ]] || continue
prefix="$(ipcalc --no-decorate -n "$addr")/''${addr##*/}"
echo "$dev: deprecating withdrawn prefix $prefix"
cat > "$conf" <<EOF
interface $dev {
AdvSendAdvert on;
@@ -158,11 +167,20 @@
};
};
EOF
rm -f "$pid"
radvd -C "$conf" -p "$pid" -n -m stderr &
sleep 7
kill -KILL $! 2>/dev/null || true
wait $! || true
for _ in 1 2 3; do
if prefixes_on "$dev" | grep -qxF "$prefix"; then
echo "$dev: $prefix is back, leaving it announced"
break
fi
echo "$dev: deprecating withdrawn prefix $prefix"
rm -f "$pid"
# radvd sends its first RA on start; the next would follow 3-4 s later.
radvd -C "$conf" -p "$pid" -n -m stderr &
sleep 1
kill -KILL $! 2>/dev/null || true
wait $! || true
sleep 2
done
done
'';
};