router-advert: T9413: add no-remove-on-exit and no-flush-* options

On shutdown radvd sends a final RA with router lifetime 0 and announces
its RDNSS and DNSSL entries with lifetime 0. On a VRRP pair that sends
RAs from a shared source address (source-address fe80::1), hosts read
the zero router lifetime as the shared router going away and remove
their default route until the backup's next RA. On my routers that was
1.6 s of IPv6 loss when the master rebooted.

radvd controls this with RemoveAdvOnExit, FlushRDNSS and FlushDNSSL,
all defaulting to on. Expose them per interface:

  set service router-advert interface <if> no-remove-on-exit
  set service router-advert interface <if> no-flush-name-server
  set service router-advert interface <if> no-flush-dnssl

The directives are only rendered when the options are set, so the
generated radvd.conf is unchanged for existing configurations.

0 files changed, 0 insertions, 0 deletions