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#1 2021-03-29 10:49:48

qupfer
Member
Registered: 2014-04-02
Posts: 11

IPv6 does not work if ULA Prefix fd00::/64 is used, but fd00::1/64

Hi,

can somebody explain, what information I miss or misunderstand?
I have two arch systems in the same network, no firewall active.

If I advertise the ULA prefix fd00::/64, I have for example these adressees:
Host A: fd00::dbbe:a16d:88e1:6f/64 ("Client")
Host B: fd00::60b4:d3ff:fe6f:ca0d/64 ("Server")

but either A or B responding to requests from each other.

qupfer@leipzig ~ % sudo tcpdump -nni br0 "icmp6 && (ip6[40] == 128 or ip6[40] == 129)"
tcpdump: verbose output suppressed, use -v[v]... for full protocol decode
listening on br0, link-type EN10MB (Ethernet), snapshot length 262144 bytes
12:33:05.986357 IP6 fd00::dbbe:a16d:88e1:6f > fd00::60b4:d3ff:fe6f:ca0d: ICMP6, echo request, id 94, seq 1, length 64
12:33:07.006991 IP6 fd00::dbbe:a16d:88e1:6f > fd00::60b4:d3ff:fe6f:ca0d: ICMP6, echo request, id 94, seq 2, length 64
12:33:08.020331 IP6 fd00::dbbe:a16d:88e1:6f > fd00::60b4:d3ff:fe6f:ca0d: ICMP6, echo request, id 94, seq 3, length 64
12:33:09.033644 IP6 fd00::dbbe:a16d:88e1:6f > fd00::60b4:d3ff:fe6f:ca0d: ICMP6, echo request, id 94, seq 4, length 64
12:33:10.047012 IP6 fd00::dbbe:a16d:88e1:6f > fd00::60b4:d3ff:fe6f:ca0d: ICMP6, echo request, id 94, seq 5, length 64

but if I advertise the prefix fd00::1/64, it works as expected.

qupfer@leipzig ~ % sudo tcpdump -nni br0 "icmp6 && (ip6[40] == 128 or ip6[40] == 129)"
tcpdump: verbose output suppressed, use -v[v]... for full protocol decode
listening on br0, link-type EN10MB (Ethernet), snapshot length 262144 bytes
12:38:45.619041 IP6 fd00::1:5ba8:5061:7e1d:7bd7 > fd00::1:60b4:d3ff:fe6f:ca0d: ICMP6, echo request, id 98, seq 1, length 64
12:38:45.619143 IP6 fd00::1:60b4:d3ff:fe6f:ca0d > fd00::1:5ba8:5061:7e1d:7bd7: ICMP6, echo reply, id 98, seq 1, length 64
12:38:46.619874 IP6 fd00::1:5ba8:5061:7e1d:7bd7 > fd00::1:60b4:d3ff:fe6f:ca0d: ICMP6, echo request, id 98, seq 2, length 64
12:38:46.619968 IP6 fd00::1:60b4:d3ff:fe6f:ca0d > fd00::1:5ba8:5061:7e1d:7bd7: ICMP6, echo reply, id 98, seq 2, length 64

So it seems, that the hosts doesn't want "random" prefix fd00:0000.0000.0000.
Is there a reason I don't see or is it just to "force" an admin to not simple use the first valid one?

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