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Posted by vicky on July 2, 2008, 9:02 am
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> > I 've query but first i write a statement of IEEE 802.1q (1998) of
> > about CFI (canonical format indicator) ...
>
> > In an Ethernet-encoded tag header, transmitted using 802.3/Ethernet
> > MAC methods, CFI has the following
> > meanings:
> > 1) =A0When set, indicates that the E-RIF field is present in the tag
> > header, and that the NCFI bit in the
> > =A0 =A0 =A0RIF determines whether MAC Address information that may be
> > present in the MAC data carried
> > =A0 =A0 =A0by the frame is in Canonical (C) or Non-canonical (N) format;=
> > 2) =A0When reset, indicates that the E-RIF field is not present in the
> > tag header, and that all MAC
> > =A0 =A0 =A0Address information that may be present in the MAC data carri=
ed
> > by the frame is in Canonical
> > =A0 =A0 =A0format (C).
>
> > --------------
> > Now my query is =A0when the CFI bit is set in case of this ethernet
> > frame.
> > please tell me
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> The CFI bit is not set in the case of Ethernet bridging Ethernet LANs.
> Ethernet uses canonical address format, therefore:
>
> 1. The CFI bit must not be set (i.e. set to 0), and
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> 2. You cannot use so-called "source routing."
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> On the other hand, if the bridge is "tunneling," or bridging, an FDDI
> frame from one FDDI LAN to another FDDI LAN, for example, and there
> are some Ethernet segments between the two FDDI LANs, then the VLAN
> tag can carry that FDDI "source routing" information. It's a way of
> allowing frames from different MACs to be bridged, without losing
> extra header information available in the non-Ethernet LANs.
>
> Here's the note in 802.1Q Clause 9 that explains this:
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> "NOTE 2=97A decision to use native source-routing on FDDI or to use an
> embedded routing information field in the VLAN tag depends on local
> knowledge in a Bridge or end station of the capabilities of the other
> stations attached to the FDDI LAN. The VLAN tag E-RIF allows source-
> routing information to be transparently 'tunneled' across LANs that do
> not support source routing and through MAC Bridges and VLAN-aware
> Bridges that discard native source-routed frames."
>
> Bert- Hide quoted text -
>
> - Show quoted text -
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What r the transparent frames
is all ethernet / 802.3 frame are said to be transparent frames....
Vikrant
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