From: John Jones (acer0001@gmail.com)
Date: Mon Nov 13 2006 - 13:04:43 ART
I would like info on this as well. I ask because I always thought that the
concept of ISL and native VLANs didn't mix. I haven't tested this though.
See below:
ISL also encapsulates the entire frame, increasing the network overhead.
Dot1q only places a header on the frame, and in some circumstances, doesn't
even do that. There is much less overhead with dot1q as compared to ISL.
That leads to the third major difference, the way the protocols work with
the native vlan.
The native vlan is simply the default vlan that switch ports are placed into
if they are not expressly placed into another vlan. On Cisco switches, the
native vlan is vlan 1. (This can be changed.) If dot1q is running, frames
that are going to be sent across the trunk line don't even have a header
placed on them; the remote switch will assume that any frame that has no
header is destined for the native vlan.
The problem with ISL is that is doesn't understand what a native vlan is.
Every single frame will be encapsulated, regardless of the vlan it's
destined for.
http://www.networkliquidators.com/article-cisco-ccna-certification-how-and-why-switches-trunk.asp
Also...
John
On 11/13/06, Alexei Monastyrnyi <alexeim@orcsoftware.com> wrote:
>
> and any details/URL to read on this?
>
> Daniel_Steyn@Dell.com wrote:
> > ISL does support a native VLAN in which ingress untagged VLANs are then
> > tagged with the vlan specified.
> >
> >
> > -----Original Message-----
> > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> > Alexei Monastyrnyi
> > Sent: Monday, November 13, 2006 9:19 AM
> > To: Rajiv
> > Cc: ccielab@groupstudy.com
> > Subject: Re: Does ISL Support...........?
> >
> > Hi.
> >
> > As per Q1, since ISL adds its specific L2 header to each frame, all
> > frames have to have it, otherwise the frame should be considered as
> > invalid. In this sense there should be no untagged frames for ISL.
> >
> > As per Q2, if I remember right, both protocols support up to 4095 VLANs.
> >
> > HTH
> > A.
> >
> > Rajiv wrote:
> >
> >> Hi all,
> >>
> >> I want to ask that Does ISL supports the processing of untagged
> >>
> > frames?
> >
> >>
> >> Also does 802.1q supports fewer VLANs than ISL?
> >>
> >> Regards,
> >> Rajiv
> >>
> >>
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