Date: Tue, 9 Mar 2021 01:58:18 -0800 From: Doug Hardie <bc979@lafn.org> To: FreeBSD Questions <freebsd-questions@freebsd.org> Subject: IPv6 Startup Message-ID: <3F059A72-F45B-43B1-8EE3-0176EE072054@sermon-archive.info>
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I have two systems on the same ethernet. One is configured as a router, = the other as a host. rtadvd is running on the router, rtsold on the = host, and route6d on both. The router was up and running and I = initiated tcpdump of ip6 packets on the interface. Then I booted the = host. The results are interesting: 22:26:17.963393 IP6 (hlim 255, next-header ICMPv6 (58) payload length: = 16) fe80::aa60:b6ff:fe1d:8dbc > ff02::2: [icmp6 sum ok] ICMP6, router = solicitation, length 16 source link-address option (1), length 8 (1): = a8:60:b6:1d:8d:bc 0x0000: 6000 0000 0010 3aff fe80 0000 0000 0000 0x0010: aa60 b6ff fe1d 8dbc ff02 0000 0000 0000 0x0020: 0000 0000 0000 0002 8500 a2b8 0000 0000 0x0030: 0101 a860 b61d 8dbc 22:26:17.997455 IP6 (hlim 255, next-header ICMPv6 (58) payload length: = 56) fe80::3e18:a0ff:fe44:765b > ff02::1: [icmp6 sum ok] ICMP6, router = advertisement, length 56 hop limit 64, Flags [none], pref medium, router lifetime 1800s, = reachable time 0ms, retrans timer 0ms source link-address option (1), length 8 (1): = 3c:18:a0:44:76:5b prefix info option (3), length 32 (4): fec2::/64, Flags = [onlink, auto], valid time 2592000s, pref. time 604800s 0x0000: 6000 0000 0038 3aff fe80 0000 0000 0000 0x0010: 3e18 a0ff fe44 765b ff02 0000 0000 0000 0x0020: 0000 0000 0000 0001 8600 8356 4000 0708 0x0030: 0000 0000 0000 0000 0101 3c18 a044 765b 0x0040: 0304 40c0 0027 8d00 0009 3a80 0000 0000 0x0050: fec2 0000 0000 0000 0000 0000 0000 0000 22:26:18.011402 IP6 (hlim 255, next-header ICMPv6 (58) payload length: = 32) :: > ff02::1:ff00:210: [icmp6 sum ok] ICMP6, neighbor solicitation, = length 32, who has fec2::210 unknown option (14), length 8 (1):=20 0x0000: cc1a 5611 b76a 0x0000: 6000 0000 0020 3aff 0000 0000 0000 0000 0x0010: 0000 0000 0000 0000 ff02 0000 0000 0000 0x0020: 0000 0001 ff00 0210 8700 9025 0000 0000 0x0030: fec2 0000 0000 0000 0000 0000 0000 0210 0x0040: 0e01 cc1a 5611 b76a 22:26:18.098774 IP6 (hlim 255, next-header ICMPv6 (58) payload length: = 32) :: > ff02::1:ff1d:8dbc: [icmp6 sum ok] ICMP6, neighbor solicitation, = length 32, who has fec2::aa60:b6ff:fe1d:8dbc unknown option (14), length 8 (1):=20 0x0000: c983 4557 f1d3 0x0000: 6000 0000 0020 3aff 0000 0000 0000 0000 0x0010: 0000 0000 0000 0000 ff02 0000 0000 0000 0x0020: 0000 0001 ff1d 8dbc 8700 f218 0000 0000 0x0030: fec2 0000 0000 0000 aa60 b6ff fe1d 8dbc 0x0040: 0e01 c983 4557 f1d3 The first packet is the host sending a router solicitation. The second = is the router responding with the advertisement with the various routes = it has. The third and fourth packets appear to be the Duplicate Address = Detection packets for the two addresses on the host. There is no = response to either. After this, a number of other packets continue on = and on. The question is, why are the host addresses being used before DAD is = attempted? It appears there could be some really interesting problems = if the link-layer address actually was duplicated. The problems would = happen before DAD was even attempted? -- Doug
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