I think there is some confusion between ISL and IEEE 802.1q.
Remember Cisco ISL VLAN ID field is 10 bits i.e. 2^10 or 1024 possible
(0-1023)
Just *think* about how many bits in an IEEE 802.1q frame it takes to make
4096 VLANs.
--- Gopinath Pulyankote <[EMAIL PROTECTED]> wrote:
> [Couldn't post this to the newsgroup, hence sending it to you directly]
>
> "Gopinath Pulyankote" <[EMAIL PROTECTED]> wrote in message news:...
> How about this ? This says 10-bit VLAN ID !
>
>
>
http://www.cisco.com/univercd/cc/td/doc/product/software/ios113ed/113ed_cr/s
> witch_c/xcisl.htm
>
> Frame Tagging in ISL
>
> With ISL, an Ethernet frame is encapsulated with a header that
> transports
> VLAN IDs between switches and routers. A 26-byte header that contains a
> 10-bit VLAN ID is prepended to the Ethernet frame.
>
> --Gopinath
>
> > ""Brant Stevens"" <[EMAIL PROTECTED]> wrote in message
> > [EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
> > >
> > > Information on ISL header... taken from
> > > http://www.cisco.com/warp/public/741/4.html
> > >
> > > VLAN - Virtual LAN ID
> > > The VLAN field is the virtual LAN ID of the packet. It is a 15-bit
> value
> > > that is used to distinguish frames on different VLANs. This field is
> often
> > > referred to as the "color" of the packet.
> > >
> > > Information on 802.1Q packet... taken from
> > >
> >
>
http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121newft/121
> > > t/121t3/dtbridge.htm#xtocid114535
> > >
> > > The tag is stored in the following two octets and it contains 3 bits
> of
> > user
> > > priority, 1 bit of Canonical Format Identifier (CFI) and 12 bits of
> VLAN
> > ID
> > > (VID). The 3 bits of user priority are used by the standard 802.1p;
> and
> > the
> > > CFI is used for compatibility reasons between Ethernet type networks
> and
> > > Token Ring type networks. The VID is the identification of the VLAN,
> which
> > > is basically used by the standard 802.1Q and, being on 12 bits, it
> allows
> > > the identification of 4096 VLANs.
> > >
> > >
> > > Brant I. Stevens
> > > Internetwork Solutions Engineer
> > > Thrupoint, Inc.
> > > 545 Fifth Avenue, 14th Floor
> > > New York, NY. 10017
> > > 646-562-6540
> > >
> > > -----Original Message-----
> > > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf
> Of
> > > Gopinath Pulyankote
> > > Sent: Wednesday, February 28, 2001 1:49 PM
> > > To: [EMAIL PROTECTED]
> > > Subject: BCMSN: VLAN ID How many bits? 10 or 15 ??
> > >
> > >
> > > Hi all,
> > > The Cisco Press book BCMSN by Karen Webb says the VLAN ID is 15
> bits,
> > > but I read somewhere else its 10 bits.
> > > Which is correct ??
> > > TIA
> > > --Gopinath
> > >
> > >
> > > _________________________________
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> >
>
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