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From: greene@coral.com (Jeremy Greene)
Newsgroups: comp.protocols.tcp-ip
Subject: Token Ring ARPs
Message-ID: <9104082218.AA00610@taipan.coral.com>
Date: 8 Apr 91 22:18:45 GMT
References: <9104082122.AA11401@ftp.com>
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
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)     But what about other applications, say for  network management, which
)     also send MAC addresses in data? A router presents the same problem as
)     a brigde in this case.
) 
) If an arbitrary protocol obtains a MAC address in a local LAN context, and
) can restrain itself from using the MAC address outside that LAN's context,
) there is no problem.  Bit order doesn't matter if you treat the address as
) opaque.  Because not all MAC addresses conform to IEEE 48 bit formats, you
) need to know the LAN's physical layer to parse them anyway.  Canonical bit
) order on all 802.2 LANs would make the parser a little simpler...
) 

You were talking about sending mac addresses accross multi-media. I was
pointing out that the problem is with ANY mac address in data, not just
macs in ARP responses. For macs in data other than ARPs, multi-media
routers cause the same problem that bridges do.

You brought up another valid issue: how does an application which
runs on various media know what the address format is. The right
answer is that it always expects it in one format. I'm not sure
what you mean by opaque, the point is that the application wants
to see the data.


) As of the moment, neither of the two widely distributed 802.5 driver specs
) (IBM's ASI and 3Com/Microsoft NDIS between them represent 95% of the IBM PC
) 802.5 interfaces, and probably 90% of the total 802.5 installed base) even
) have hooks in them to indicate which bit order the MAC address is presented
) in. Many of the ASI drivers are at least partly in ROM.  So, first you need
) to upgrade the specs, then all software drivers that were shipped with the
) boards, and maybe the ROMs.  It'll be a while.

Is it really that bad? You mean there are 802.5 cards/drivers which
actually return a canonical format address? I find that hard to believe.
It would certainly be nice to have the driver hook, but I think the 
client of the driver could know the format based on the interface
type.

JAG