radvd.conf syntax error - won't start

[motific]

radvd does not start on startup and if I try to start it I getting the an error in the syslog -

/status_services.php: The command '/usr/local/sbin/radvd -p /var/run/radvd.pid -C /var/etc/radvd.conf -m syslog' returned exit code '1', the output was '/var/etc/radvd.conf:11 error: syntax error' 

The radvd.conf file is auto-generated and I haven't altered it though any changes should get wiped. It is:-

# Automatically Generated, do not edit
# Generated for DHCPv6 Server lan
interface re1 {
	AdvSendAdvert on;
	MinRtrAdvInterval 5;
	MaxRtrAdvInterval 20;
	AdvLinkMTU 1500;
	AdvDefaultPreference medium;
	AdvManagedFlag on;
	AdvOtherConfigFlag on;
	prefix ::101:101/128 {  # error is on this line?
		DeprecatePrefix on;
		AdvOnLink on;
		AdvAutonomous on;
		AdvRouterAddr on;
		AdvValidLifetime 86400;
		AdvPreferredLifetime 14400;
	};
	route ::/0 {
		AdvRoutePreference medium;
		RemoveRoute on;
	};
	RDNSS ::10.10.10.1 { };
	DNSSL lan  { };
};

I'm on 2.4.5 dev snapshots (build 2.4.5.a.20190213.0609) so if it's related to that then let me know.

[jimp]

You shouldn't be getting a /128 prefix delegated. That isn't valid to use for SLAAC advertising and so on, it has to be a /64. That's also not a complete prefix specification.

Is that coming from upstream or somewhere in your configuration?

[motific]

I haven't specified it anywhere so I presume it is coming from upstream, though I'd need some guidance on how to check it properly.

[jimp]

Set Debug in the DHCP6 Client Configuration on WAN as well, then check the logs (main system log, routing log, etc) to see what shows up.