From: Tim (ccie2be@nyc.rr.com)
Date: Thu Dec 01 2005 - 09:06:29 GMT-3
Sholy,
From the point of view of the R&S lab, there are really only 2 things you
need to know regarding the differences between 802.1q and ISL:
- 802.1q is standards based, ISL is proprietary.
- 802.1q defines a "native" vlan, while ISL has no concept of "native" vlan.
This last point is critical to understand because it has configuration
implications you must be aware of including among other things that the
native vlan must be the same on both sides of the link.
Make sure you know every command that can be used to change the native vlan
and make sure you know the ramifications of using one command versus
another.
HTH, Tim
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
sholy augustine
Sent: Thursday, December 01, 2005 2:45 AM
To: ccielab@groupstudy.com
Subject: ISL Vs 802.1Q
Hi,
I have some confusion regarding the difference between
ISL and dot1q encapsulation. As to my knowledge ISL
uses only 10bits (although 15 bits is reserved) for
VLAN ID giving total of 1024 VLAN IDs and dot1q uses
12 bits giving a total of 4096 VLANs.
When I configure a trunk between 2 3550 switches, I
don't see any difference between them both in show
outputs and in functionality
For both ISL and dot1q the allowed VLAN on the trunk
is up to 4096. This is an expected behaviour for
dot1q, but for ISL why is it giving 4096, should it
not be 1024 only
Also for ISL encapsulation, native VLAN ID is provided
Kind Regards,
Sholy
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