Wireshark · Wireshark-bugs: [Wireshark-bugs] [Bug 1455] LLDPDU MAC-PHY TLV PMD Auto-Neg field is being analyzed incorrectly

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http://bugs.wireshark.org/bugzilla/show_bug.cgi?id=1455





------- Comment #9 from guy@xxxxxxxxxxxx  2007-04-10 17:16 GMT -------
> There are 16 bits for this field in the TLV numbered 0-15 counting from right to left.

As I read RFC 3636, the SNMP field that the 802.1AB-2005 spec says is the model
for the LLDP field has "SYNTAX BITS", and, as I read RFC 1906, a "SYNTAX BITS"
field in SNMP is an OCTET STRING, i.e. a sequence of bytes, and the bits from
the enumeration are put in order from the first bit of the first octet through
the last bit of the first octet, and then, if there's a second octet, in order
from the first bit of the second octet through the last bit of the second
octet, etc..

I.e. the first bit in the enumeration is in the topmost bit of the first octet,
and the next up-to-7 bits are in the rest of the bits of the octet, and any 9th
bit is in the topmost bit of the second octet, etc..

This means that the field isn't a 16-bit integral value - it's two octets in
sequence.

I.e., if something is fetched as big-endian and displays as 0x0136, it would be
the two bytes

  8  7  6  5  4  3  2  1    8  7  6  5  4  3  2  1

  0  0  0  0  0  0  0  1    0  0  1  1  0  1  1  0

which correspond in sequence to

                                            1  1  1  1  1  1
  0  1  2  3  4  5  6  7    8  9  0  1  2  3  4  5

The values in the enumeration are, in order:

  bOther(0),
  b10baseT(1),
  b10baseTFD(2),
  b100baseT4(3),
  b100baseTX(4),
  b100baseTXFD(5),
  b100baseT2(6),
  b100baseT2FD(7),
  bFdxPause(8),
  bFdxAPause(9),
  bFdxSPause(10),
  bFdxBPause(11),
  b1000baseX(12),
  b1000baseXFD(13),
  b1000baseT(14),
  b1000baseTFD(15)

so the values corresponding to the bits that are set are:

  b100baseT2FD
  bFdxSPause
  bFdxBPause
  b1000baseXFD
  b1000baseT


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