Sorry, I didn't mean to imply you personally were confused.
Come to think of it, ALL the documentation should be clearer.
Particularly if you think about the 15bits plus the 1bit BPDU field in
the ISL are so close to the 2 bytes in an 802.1q VLAN Identifier header
(3 Priority, 1 CFI, 12 ID)...which was the direction I thought people
were heading towards...
On Wed, Feb 28, 2001 at 03:04:13PM -0800, Gopinath Pulyankote wrote:
>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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>> >
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