From: Alexei Monastyrnyi (alexeim@orcsoftware.com)
Date: Mon Nov 13 2006 - 15:40:01 ART
exactly!
cheers, mate! :-)
Venkatesh Venkatesh wrote:
> All frames should be tagged in ISL bit not the case is 802.1Q
>
> REF cisco.com
>
> "In an ISL trunk port, all received packets are expected to be encapsulated
> with an ISL header, and all transmitted packets are sent with an ISL header.
> Native (non-tagged) frames received from an ISL trunk port are dropped.
>
> An IEEE 802.1Q trunk port supports simultaneous tagged and untagged
> traffic. An 802.1Q trunk port is assigned a default Port VLAN ID (PVID), and
> all untagged traffic travels on the port default PVID. All untagged traffic
> and tagged traffic with a NULL VLAN ID are assumed to belong to the port
> default PVID. A packet with a VLAN ID equal to the outgoing port default
> PVID is sent untagged. All other traffic is sent with a VLAN tag.
> "
>
>
> - Venkatesh
>
>
> On 11/13/06, Daniel_Steyn@dell.com <Daniel_Steyn@dell.com> wrote:
>
>> Well...it does LET you configure a native vlan on ISL. Having said
>> that, ISL will ALWAYS tag egress traffic - even the "native" vlan. My
>> belief is that (correct me if I am wrong, please) the native VLAN will
>> mark INGRESS UNTAGGED traffic with the specified native vlan value. I
>> do understand that between 2 switches running ISL, there should be no
>> untagged traffic (they tag all VLANs), however, some NICs do allow you
>> to run ISL in which the possibility of untagged traffic is present. But
>> even if that were the case...traffic would be tagged upon the return, so
>> I'm not sure to be honest. We'll have to fire it up in a lab and test.
>>
>> switch> (enable) show trunk 1/3
>> * - indicates vtp domain mismatch
>> # - indicates dot1q-all-tagged enabled on the port
>> $ - indicates non-default dot1q-ethertype value
>> Port Mode Encapsulation Status Native vlan
>> -------- ----------- ------------- ------------ -----------
>> 1/3 on isl trunking* 400
>>
>> Port Vlans allowed on trunk
>> --------
>> ---------------------------------------------------------------------
>> 1/3
>> 4-7,9-12,26-27,34-35,39-40,76,87-88,90,93,127,134,187,200,216-217,220,23
>> 3,251,255,399-402,408,410,415,500,725,802,874,985
>>
>> Brian/Scott or some of the other serious gurus may be able to provide us
>> with the answer on this one.
>>
>>
>> ________________________________
>>
>> From: John Jones [mailto:acer0001@gmail.com]
>> Sent: Monday, November 13, 2006 10:05 AM
>> To: ccielab@groupstudy.com; Steyn, Daniel
>> Subject: Does ISL Support...........?
>>
>>
>> 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-a
>> nd-why-switches-trunk.asp
>>
>> Also...
>>
>> http://www.ezinearticles.com/?Cisco-CCNA-/-CCNP-/-BCMSN-Exam-Review:--Tr
>> unking-And-Trunking-Protocols&id=195572
>>
>> 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
>> >>
>> >>
>> >> ---------------------------------
>> >> Everyone is raving about the all-new Yahoo! Mail beta.
>> >>
>> >>
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