My Q was related to ISL only. IEEE 802.1q has 12 bits, that's clear.
After reading some of the replies, I can summarize ISL's VLAN ID as:
15 bits are allocated for the field but only 10 are used now.
"anthony kim" <[EMAIL PROTECTED]> wrote in message
[EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
> 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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