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 #5 from guy@xxxxxxxxxxxx  2007-04-10 09:07 GMT -------
IEEE Std 802.1AB-2005 says:

G.2.2 PMD auto-negotiation advertised capability field 
The PMD auto-negotiation advertised capability field shall contain an integer
value as defined by the 
ifMauAutoNegCapAdvertisedBits object in IETF RFC 3636. 

RFC 3636 says:

ifMauAutoNegCapAdvertisedBits OBJECT-TYPE
           SYNTAX      BITS {
               bOther(0),        -- other or unknown
               b10baseT(1),      -- 10BASE-T  half duplex mode
               b10baseTFD(2),    -- 10BASE-T  full duplex mode
               b100baseT4(3),    -- 100BASE-T4
               b100baseTX(4),    -- 100BASE-TX half duplex mode
               b100baseTXFD(5),  -- 100BASE-TX full duplex mode
               b100baseT2(6),    -- 100BASE-T2 half duplex mode
               b100baseT2FD(7),  -- 100BASE-T2 full duplex mode
               bFdxPause(8),     -- PAUSE for full-duplex links
               bFdxAPause(9),    -- Asymmetric PAUSE for full-duplex
                                 --     links
               bFdxSPause(10),   -- Symmetric PAUSE for full-duplex
                                 --     links
               bFdxBPause(11),   -- Asymmetric and Symmetric PAUSE for
                                 --     full-duplex links
               b1000baseX(12),   -- 1000BASE-X, -LX, -SX, -CX half
                                 --     duplex mode
               b1000baseXFD(13), -- 1000BASE-X, -LX, -SX, -CX full
                                 --     duplex mode
               b1000baseT(14),   -- 1000BASE-T half duplex mode
               b1000baseTFD(15)  -- 1000BASE-T full duplex mode
           }

RFC 1906 says:

   (3)  When encoding an object whose syntax is described using the BITS
        construct, the value is encoded as an OCTET STRING, in which all
        the named bits in (the definition of) the bitstring, commencing 
        with the first bit and proceeding to the last bit, are placed in
        bits 8 to 1 of the first octet, followed by bits 8 to 1 of each
        subsequent octet in turn, followed by as many bits as are needed of
        the final subsequent octet, commencing with bit 8.  Remaining bits,
        if any, of the final octet are set to zero on generation and
        ignored on receipt.

ITU-T Recommendation X.690 says:

6.2 For the purposes of this Recommendation | International Standard only, the
bits of an octet are numbered from 
8 to 1, where bit 8 is the "most significant bit", and bit 1 is the "least
significant bit". 

>From this, I conclude that bOther is the MSB of the first octet, b10baseT is
the next octet down, and so on.  That would make a field value of 0x0136 as
being:

    b100baseT2FD, bfdxSPause, bfdxBPause, b1000baseXFD, b1000baseT

I.e., at least as I read the standards in question, Wireshark is dissecting the
packet correctly, and if that's not what the folks at Avaya intended, they
misread the standard.


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