>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
From the horse's mouth, 802.1Q:
9.1 Overview
Tagging a frame requires:
a) The addition of a Tag Header to the frame. This header is inserted
immediately following the Desti-nation
MAC address and Source MAC address (and Routing, if present) fields
of the frame to be
transmitted;
To return to your original question, Ole, when you speak of
optimizing resource use, what do you consider the scarce resource?
Other than in the martini-soaked brain (if I may use the term) of an
overly zealous salesdroid, you can't optimize for everything at once.
Save me from "specialists in all cars, foreign and domestic."
Some optimizations could include:
Bandwidth overhead
Frame length
Overhead frames (BPDU, for example)
Latency in the switch
Input serialization
Processing
Internal forwarding
Output serialization
Ease of use
Interoperability
Which do you want to optimize?
>
>
>-----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
>
>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
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