Ole,
Thanks for straightening me out. I was misled by the Exam Cram book. On
reading more about 802.1q in the Clark/Hamilton Cisco Lan Switching book I
see that 4 bytes are added. Interestingly, they note that the IEEE has
formed a workgroup 802.3ac to extend ethernet maximum frame size to 1522
octets to take care of the baby giant issue.
Thanks again for increasing my understanding.
Tom
"Ole Drews Jensen" <[EMAIL PROTECTED]> wrote in message
2019FB428FD3D311893700508B71EBFB2C5B5D@RWR_MAIL_SVR">news:2019FB428FD3D311893700508B71EBFB2C5B5D@RWR_MAIL_SVR...
> Thanks for your reply Tom,
>
> However, according to the book I'm reading, the 802.1Q DOES change the
frame
> size by adding 4 bytes into it.
>
> Take care,
>
> Ole
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> Ole Drews Jensen
> Systems Network Manager
> CCNA, MCSE, MCP+I
> RWR Enterprises, Inc.
> [EMAIL PROTECTED]
> http://www.insync.net/~drews/ccnp
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
>
>
>
> -----Original Message-----
> From: Tom Walstrom [mailto:[EMAIL PROTECTED]]
> Sent: Friday, September 08, 2000 6:30 AM
> To: Ole Drews Jensen; [EMAIL PROTECTED]
> Subject: RE: 802.1Q or ISL
>
>
> Ole,
>
> ISL encapsulates the frame adding, as you said, a 26 byte header and a 4
> byte CRC trailer. 802.1Q frame-tagging does not change the frame size
> (hence its interoperability, because it appears as a standard ethernet
frame
> to non-802.1Q devices), but does modify the existing frame with VLAN
> identification information.
>
> I would suspect that the real reason to deploy ISL is that it runs one
> spanning tree per vlan where 802.1Q runs only one spanning tree. Also ISL
> allows bonding into etherchannels. Seems like this would be more likely
to
> make a difference on the network. I would think you would only do 802.1Q
> where interoperability was the issue, like with a Catalyst 4000 which I
> believe only supports 802.1Q. Maybe some switch guru could further
> illuminate this issue.
>
> Regards,
>
> Tom
>
> -----Original Message-----
> From: Ole Drews Jensen [mailto:[EMAIL PROTECTED]]
> Sent: Thursday, September 07, 2000 1:38 PM
> To: '[EMAIL PROTECTED]'
> Subject: 802.1Q or ISL
>
>
> Just a thought. - Digging through another book towards the light at the
end
> of the tunnel, I have now added VLAN Trunc Links to my knowledge. That has
> brought this question up in my mind, so I would like to hear some feedback
> on this subject.
>
> I know that much of this depends on the average frame sizes, so lets say
> that I have analyzed my network, and the average frame size is 800. Lets
> also say that we are only dealing with Cisco Catalyst switches in this
> scenario.
>
> The question is, what would be least resource-waste to use as a trunking
> link : ISL or 802.1Q???
>
> The 802.1Q has to break the frame open to modify it, but it adds only 4
> bytes to each frame.
>
> The ISL does not have to break the frame open because it simply
encapsulates
> it into a new one, but it adds 30 bytes to each frame.
>
> Any comments on this?
>
> Thanks,
>
> Ole
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~
> Ole Drews Jensen
> Systems Network Manager
> CCNA, MCSE, MCP+I
> RWR Enterprises, Inc.
> [EMAIL PROTECTED]
> ~~~~~~~~~~~~~~~~~~~~~~~~~~
>
>
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