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Date:      Fri, 17 Sep 1999 18:07:04 +0200
From:      Thierry Herbelot <thierry.herbelot@alcatel.fr>
Cc:        freebsd-atm@FreeBSD.ORG, harp@magic.net
Subject:   [OT, long] Xylan switch, Fore PCA-200, NT and bridged RFC1483
Message-ID:  <37E26728.5AAA2F45@alcatel.fr>
References:  <199909102016.PAA15877@plains.NoDak.edu>

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Hello,

As said in the subject, the question is (more than slightly) off-topic,
but the setup I have won't work with anything other than NT, I fear.

I'm trying to connect two PCs :
- one has an Ethernet interface and is connected to an Ethernet module
of a Xylan switch (1100-LSS).
- the other has a ATM interface (Fore PCA-200e) and its driver is
configured as RFC-1483 in bridged mode. The fore adapter is also
connected to the same Xylan switch.
(as it was said in a recent post on atm@freebsd.org by Marc Tinguely,
there is no bridged stack on FreeBSD)

The Ethernet port of the switch is configured to be in the same VLAN
group as the ATM port, and the group is configured as a point-to-point
bridge.

We have a RadCom analyser, connected between the switch and the PCA
adapter 

When we try to ping the Ethernet PC from the ATM PC, we see the
following :
- an encapsulated echo request is sent via the ATM fiber, is
de-encpasulated by the switch, sent over the Ethernet, and then received
py the Ethernet PC
- the Ethernet PC replies, the Ethernet frame is encapsulated by the
switch, is sent over the ATM fiber, but is not seen from the Fore
adapter.

upon closer examination, we have seen that the Ethernet frame sent by
the PCA adapter is sent without Ethernet FCS, and the Ethernet FCS is
added when the frame is sent over the Ethernet port, but the frame on
the return trip is encapsulated with the FCS.

When we look at the PDUs sent when pinging from an ATM PC to another ATM
PC, there is no Ethernet FCS in the encapsulated frames (there is in
this case a good connection between the two machines).

The question is then : 
does the Fore ATM driver discard frames which are encapsulated as said
in the RFC1483, but which include the Ethernet FCS ? (the two
possibilities are legal, when you read the RFC)

	Thanks in advance for those patient enough to read the full post

	TfH


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