I have a new GL-S20 running the beta firmware for thread, and it’s behavior seems to be that it creates two ULA ranges, announcing one onto the local segment and another for thread which is routed:
A packet capture shows:
09:48:52.296848 IP6 (hlim 255, next-header ICMPv6 (58) payload length: 72) fe80::9683:c4ff:fe77:534b > ff02::1: [icmp6 sum ok] ICMP6, router advertisement, length 72
hop limit 0, Flags [none], pref medium, router lifetime 0s, reachable time 0ms, retrans timer 0ms
unknown option (26), length 8 (1):
0x0000: 8000 0000 0000
prefix info option (3), length 32 (4): fd7f:c9af:93f8:8781::/64, Flags [onlink, auto], valid time 1800s, pref. time 1800s
0x0000: 40c0 0000 0708 0000 0708 0000 0000 fd7f
0x0010: c9af 93f8 8781 0000 0000 0000 0000
route info option (24), length 16 (2): fdb0:7e66:f03e:1::/64, pref=medium, lifetime=1800s
0x0000: 4000 0000 0708 fdb0 7e66 f03e 0001
The first problem is this network already has working IPv6, so the fd7f:c9af:93f8:8781::/64 is not needed at all as the device can use its address from the parent network.
Second is the fdb0:7e66:f03e:1::/64 route, iOS devices seem to pick this up as a default route despite it being for a specific prefix, breaking connectivity on these devices.
There is also no need to use ULA here as the upstream router supports DHCPv6-PD. Apple devices such as the Apple TV work this way with their thread support, using PD if available. This ensures that the router inserts a proper route to the delegated address block.
The GL-S20 doesn’t seem to allow manual configuration of IPv6, despite the fact that IPv6 is essential for matter/thread, on the other hand it allows legacy IP configuration which is completely redundant and would be better turned off.
So the following questions/suggestions:
- can we disable legacy IP entirely as it serves no purpose for thread/matter
- can we get support for DHCPv6-PD so the device gets a routable prefix to use for the thread network?
