Node soliciting neighbour twice, results in duplicate IPv6 address

martin f krafft <[email protected]> Sun, 3 Jan 2016 10:48:13 +1300

Newsgroups	gmane.linux.debian.devel.ipv6
Organization	The Debian project
Message-ID	<[email protected]>

Hi folks,

Happy New Year to start with.

My laptop is hooking up to a no-frills WLAN behind a Debian router
advertising a prefix using radvd. I've used this laptop for years in
similar situations, but this time I am seeing the kernel warn about
duplicate IPv6 addresses being detected:

  IPv6: wifi: IPv6 duplicate address 2001:4428:29c:0:2ad2:44ff:fe8c:5bd detected!

I've unplugged/disconnected all other devices and yet the problem
persists. Hence I fired up tcpdump and captured the ICMPv6 packages.
And curiously, the laptop is sending two solicitations, one to the
multicast MAC address 33:33:ff:* and the other *to itself*!

Attached are the two packet dumps, and here's a diff between them,
with timestamps and identical stuff stripped:

  -Frame 1: 78 bytes on wire (624 bits), 78 bytes captured (624 bits) on interface 0
  +Frame 2: 78 bytes on wire (624 bits), 78 bytes captured (624 bits) on interface 0
  […]
  -Ethernet II, Src: 28:d2:44:8c:05:bd, Dst: 33:33:ff:8c:05:bd
  -    Destination: 33:33:ff:8c:05:bd
  -        Address: 33:33:ff:8c:05:bd
  -        .... ..1. .... .... .... .... = LG bit: Locally administered address (this is NOT the factory default)
  -        .... ...1 .... .... .... .... = IG bit: Group address (multicast/broadcast)
  +Ethernet II, Src: 28:d2:44:8c:05:bd, Dst: 28:d2:44:8c:05:bd
  +    Destination: 28:d2:44:8c:05:bd
  +        Address: 28:d2:44:8c:05:bd
  +        .... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
  +        .... ...0 .... .... .... .... = IG bit: Individual address (unicast)

Correct me if I am wrong, but that second frame should not be sent,
right? Why would the node send a solicitation to itself?

Unfortunately, I have no idea where this is coming from. I've
disabled all bridges. This is Debian's 4.3.0-1-amd64 kernel
(4.3.3-1).

Do you have any clue what might be going on?

-- 
 .''`.   martin f. krafft <[email protected]> @martinkrafft
: :'  :  proud Debian developer
`. `'`   http://people.debian.org/~madduck
  `-  Debian - when you have better things to do than fixing systems
 
"most people become bankrupt through having invested too heavily in
 the prose of life. to have ruined one's self over poetry is an
 honour."
                                                      -- oscar wilde

frame1.txt (text/plain, 2.1 KB)

Frame 1: 78 bytes on wire (624 bits), 78 bytes captured (624 bits) on interface 0
    Interface id: 0 (wifi)
    Encapsulation type: Ethernet (1)
    Arrival Time: Jan  3, 2016 10:25:50.168744045 NZDT
    [Time shift for this packet: 0.000000000 seconds]
    Epoch Time: 1451769950.168744045 seconds
    [Time delta from previous captured frame: 0.000000000 seconds]
    [Time delta from previous displayed frame: 0.000000000 seconds]
    [Time since reference or first frame: 0.000000000 seconds]
    Frame Number: 1
    Frame Length: 78 bytes (624 bits)
    Capture Length: 78 bytes (624 bits)
    [Frame is marked: False]
    [Frame is ignored: False]
    [Protocols in frame: eth:ethertype:ipv6:icmpv6]
Ethernet II, Src: 28:d2:44:8c:05:bd, Dst: 33:33:ff:8c:05:bd
    Destination: 33:33:ff:8c:05:bd
        Address: 33:33:ff:8c:05:bd
        .... ..1. .... .... .... .... = LG bit: Locally administered address (this is NOT the factory default)
        .... ...1 .... .... .... .... = IG bit: Group address (multicast/broadcast)
    Source: 28:d2:44:8c:05:bd
        Address: 28:d2:44:8c:05:bd
        .... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
        .... ...0 .... .... .... .... = IG bit: Individual address (unicast)
    Type: IPv6 (0x86dd)
Internet Protocol Version 6, Src: ::, Dst: ff02::1:ff8c:5bd
    0110 .... = Version: 6
    .... 0000 0000 .... .... .... .... .... = Traffic class: 0x00 (DSCP: CS0, ECN: Not-ECT)
        .... 0000 00.. .... .... .... .... .... = Differentiated Services Codepoint: Default (0)
        .... .... ..00 .... .... .... .... .... = Explicit Congestion Notification: Not ECN-Capable Transport (0)
    .... .... .... 0000 0000 0000 0000 0000 = Flowlabel: 0x00000000
    Payload length: 24
    Next header: ICMPv6 (58)
    Hop limit: 255
    Source: ::
    Destination: ff02::1:ff8c:5bd
    [Source GeoIP: Unknown]
    [Destination GeoIP: Unknown]
Internet Control Message Protocol v6
    Type: Neighbor Solicitation (135)
    Code: 0
    Checksum: 0x997e [correct]
    Reserved: 00000000
    Target Address: 2001:4428:29c:0:2ad2:44ff:fe8c:5bd

frame2.txt (text/plain, 2 KB)

Frame 2: 78 bytes on wire (624 bits), 78 bytes captured (624 bits) on interface 0
    Interface id: 0 (wifi)
    Encapsulation type: Ethernet (1)
    Arrival Time: Jan  3, 2016 10:25:50.169511800 NZDT
    [Time shift for this packet: 0.000000000 seconds]
    Epoch Time: 1451769950.169511800 seconds
    [Time delta from previous captured frame: 0.000767755 seconds]
    [Time delta from previous displayed frame: 0.000767755 seconds]
    [Time since reference or first frame: 0.000767755 seconds]
    Frame Number: 2
    Frame Length: 78 bytes (624 bits)
    Capture Length: 78 bytes (624 bits)
    [Frame is marked: False]
    [Frame is ignored: False]
    [Protocols in frame: eth:ethertype:ipv6:icmpv6]
Ethernet II, Src: 28:d2:44:8c:05:bd, Dst: 28:d2:44:8c:05:bd
    Destination: 28:d2:44:8c:05:bd
        Address: 28:d2:44:8c:05:bd
        .... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
        .... ...0 .... .... .... .... = IG bit: Individual address (unicast)
    Source: 28:d2:44:8c:05:bd
        Address: 28:d2:44:8c:05:bd
        .... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
        .... ...0 .... .... .... .... = IG bit: Individual address (unicast)
    Type: IPv6 (0x86dd)
Internet Protocol Version 6, Src: ::, Dst: ff02::1:ff8c:5bd
    0110 .... = Version: 6
    .... 0000 0000 .... .... .... .... .... = Traffic class: 0x00 (DSCP: CS0, ECN: Not-ECT)
        .... 0000 00.. .... .... .... .... .... = Differentiated Services Codepoint: Default (0)
        .... .... ..00 .... .... .... .... .... = Explicit Congestion Notification: Not ECN-Capable Transport (0)
    .... .... .... 0000 0000 0000 0000 0000 = Flowlabel: 0x00000000
    Payload length: 24
    Next header: ICMPv6 (58)
    Hop limit: 255
    Source: ::
    Destination: ff02::1:ff8c:5bd
    [Source GeoIP: Unknown]
    [Destination GeoIP: Unknown]
Internet Control Message Protocol v6
    Type: Neighbor Solicitation (135)
    Code: 0
    Checksum: 0x997e [correct]
    Reserved: 00000000
    Target Address: 2001:4428:29c:0:2ad2:44ff:fe8c:5bd

digital_signature_gpg.asc (application/pgp-signature, 1.1 KB)