This makes the rDNS lifetime the same as the router lifetime (1800
seconds). rad(8) already lists 8106 under standards, but we used the old
value from 6106.
It also does not make any sense to expire the rDNS information before
the router itself. This is information that travels together.

OK?

diff --git rad.conf.5 rad.conf.5
index b90934603f7..8abd51b9bed 100644
--- rad.conf.5
+++ rad.conf.5
@@ -76,7 +76,7 @@ options are as follows:
 .It Ic lifetime Ar seconds
 The number of seconds the dns options are valid after receiving a router
 advertisement message.
-The default is 900 seconds.
+The default is 1800 seconds.
 .It Ic nameserver Pq Ar address Ns | Ns Brq Ar address ...
 IPv6 address or list of IPv6 addresses of DNS name servers.
 .It Ic search Pq Ar domain Ns | Ns Brq Ar domain ...
diff --git rad.h rad.h
index 46cdc51ea64..e0e59a31a38 100644
--- rad.h
+++ rad.h
@@ -34,7 +34,7 @@
 #define	MAX_RA_DELAY_TIME	500	/* 500 milliseconds */
 #define	MIN_DELAY_BETWEEN_RAS	3	/* 3 seconds */
 #define	MAX_SEARCH		1025	/* MAXDNAME in arpa/nameser.h */
-#define	DEFAULT_RDNS_LIFETIME	600 * 1.5
+#define	DEFAULT_RDNS_LIFETIME	3 * MAX_RTR_ADV_INTERVAL
 #define	PLTIME_DECAYING		1
 #define	VLTIME_DECAYING		2
 

-- 
In my defence, I have been left unsupervised.