IPv6 Startup

[Doug Hardie]

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): 
	  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): 
	  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