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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