«

A lot of people ask native vlan question.
I think using "vlan dot1q tag native" should eliminate this question.
at least for sw---sw connection. (all tagged just like isl)
I may not fully understand what's purpose why cisco make "native
vlan".
Some article say because of backward compatible with 802.3.
Can anyone give an example?

TIA,
st

On Apr 15, 3:51 am, aaabb...@hotmail.com wrote:
> A lot of people ask native vlan question.
> I think using "vlan dot1q tag native" should eliminate this question.
> at least for sw---sw connection. (all tagged just like isl)
> I may not fully understand what's purpose why cisco make "native
> vlan".
> Some article say because of backward compatible with 802.3.
> Can anyone give an example?
>
> TIA,
> st

Here are some good posts on this topic. Probably better than one of
us typing up several paragraphs. The second article explains native
vlan / vlan 1, and management interface concerns.

http://www.velocityreviews.com/forum...tive-vlan.html
http://www.velocityreviews.com/forum...lan-1quot.html

On 4ÔÂ15ÈÕ, ÉÏÎç4ʱ13·Ö, Trendkill <jpma...@gmail.com> wrote:
> On Apr 15, 3:51 am, aaabb...@hotmail.com wrote:
>
> > A lot of people ask native vlan question.
> > I think using "vlan dot1q tag native" should eliminate this question.
> > at least for sw---sw connection. (all tagged just like isl)
> > I may not fully understand what's purpose why cisco make "native
> > vlan".
> > Some article say because of backward compatible with 802.3.
> > Can anyone give an example?
>
> > TIA,
> > st
>
> Here are some good posts on this topic. Probably better than one of
> us typing up several paragraphs. The second article explains native
> vlan / vlan 1, and management interface concerns.
>
> http://www.velocityreviews.com/forum...-management-vl...

Still confuse something.

[sp3gcf]

Cisco's proprietary ISL doesn't support Natvie Vlan, an IEEE's 802.1Q does support Native Vlan and was intorduced years later..

-Tom

<> wrote in message
news:123637df-5ec8-499a-a32c-...
> A lot of people ask native vlan question.
> I think using "vlan dot1q tag native" should eliminate this question.
> at least for sw---sw connection. (all tagged just like isl)
> I may not fully understand what's purpose why cisco make "native
> vlan".

cisco didnt invent this - it is part of 802.1Q.

> Some article say because of backward compatible with 802.3.

i suggest you try to find the standard and read around that,
maybe start at www.ieee.org

AFAIR some of the standards docs are without charge for Ethernet.

> Can anyone give an example?

there are 2 Qs to think about.

1. set a port to be tagged
- what do you do with a packet that arrives with no tag?

the 2 common answers are to throw it away, or to put it into some sort of
"default VLAN" - that is what untagged means for incoming packets.

not putting a tag on outbound packets form that VLAN on that port allows 2
way comms.

this sounds silly - but it is what often needs to happen when you hook up an
unconfigured device to set it up.

2. what happens when you want to split up 2 streams of packets on a port?

sometimes you have a device that will add its own stream of packets to a set
it gets from elsewhere
- the classic case is an IP phone where there is a plug on the phone to
connect a PC.
- Pcs dont normally send tagged frames, and the 3 port bridge in the phone
doesnt have the horsepower to wrap a tag around every packet.
- but you want the phone traffic kept separate from PC (security, QoS and
so on).

So - pass the PC packet thru untagged, and tag the phone traffic.
At the switch the PC "stuff" is untagged and goes into the native VLAN,
phone traffic is tagged and goes into a different VLAN.
>
> TIA,
> st
>
--
Regards

- replace xyz with ntl

On 4ÔÂ15ÈÕ, ÏÂÎç1ʱ13·Ö, "stephen" <stephen_h...@xyzworld.com> wrote:
> <aaabb...@hotmail.com> wrote in message
>
> news:123637df-5ec8-499a-a32c-...
>
> > A lot of people ask native vlan question.
> > I think using "vlan dot1q tag native" should eliminate this question.
> > at least for sw---sw connection. (all tagged just like isl)
> > I may not fully understand what's purpose why cisco make "native
> > vlan".
>
> cisco didnt invent this - it is part of 802.1Q.
>
> > Some article say because of backward compatible with 802.3.
>
> i suggest you try to find the standard and read around that,
> maybe start atwww.ieee.org
>
> AFAIR some of the standards docs are without charge for Ethernet.
>
> > Can anyone give an example?
>
> there are 2 Qs to think about.
>
> 1. set a port to be tagged
> - what do you do with a packet that arrives with no tag?
>
> the 2 common answers are to throw it away, or to put it into some sort of
> "default VLAN" - that is what untagged means for incoming packets.
>
> not putting a tag on outbound packets form that VLAN on that port allows 2
> way comms.
>
> this sounds silly - but it is what often needs to happen when you hook up an
> unconfigured device to set it up.
>
> 2. what happens when you want to split up 2 streams of packets on a port?
>
> sometimes you have a device that will add its own stream of packets to a set
> it gets from elsewhere
> - the classic case is an IP phone where there is a plug on the phone to
> connect a PC.
> - Pcs dont normally send tagged frames, and the 3 port bridge in the phone
> doesnt have the horsepower to wrap a tag around every packet.
> - but you want the phone traffic kept separate from PC (security, QoS and
> so on).
>
> So - pass the PC packet thru untagged, and tag the phone traffic.
> At the switch the PC "stuff" is untagged and goes into the native VLAN,
> phone traffic is tagged and goes into a different VLAN.
>
> > TIA,
> > st
>
> --
> Regards
>
> stephen_h...@xyzworld.com - replace xyz with ntl

Thanks,
For "Some article say because of backward compatible with 802.3"
they may think far end is Hub or switch/bridge which does not support
802.3,
right?
One more question, when a access port receive a untag frame, does it
add
a 802.1q tag or some other tag to make sure it can go same vlan inside
of
this switch?

On 16 Apr, 05:31, aaabb...@hotmail.com wrote:
> On 4ÔÂ15ÈÕ, ÏÂÎç1ʱ13·Ö, "stephen" <stephen_h...@xyzworld.com> wrote:
>
>
>
>
>
> > <aaabb...@hotmail.com> wrote in message
>
> >news:123637df-5ec8-499a-a32c-...
>
> > > A lot of people ask native vlan question.
> > > I think using "vlan dot1q tag native" should eliminate this question.
> > > at least for sw---sw connection. (all tagged just like isl)
> > > I may not fully understand what's purpose why cisco make "native
> > > vlan".
>
> > cisco didnt invent this - it is part of 802.1Q.
>
> > > Some article say because of backward compatible with 802.3.
>
> > i suggest you try to find the standard and read around that,
> > maybe start atwww.ieee.org
>
> > AFAIR some of the standards docs are without charge for Ethernet.
>
> > > Can anyone give an example?
>
> > there are 2 Qs to think about.
>
> > 1. set a port to be tagged
> > - what do you do with a packet that arrives with no tag?
>
> > the 2 common answers are to throw it away, or to put it into some sort of
> > "default VLAN" - that is what untagged means for incoming packets.
>
> > not putting a tag on outbound packets form that VLAN on that port allows 2
> > way comms.
>
> > this sounds silly - but it is what often needs to happen when you hook up an
> > unconfigured device to set it up.
>
> > 2. what happens when you want to split up 2 streams of packets on a port?
>
> > sometimes you have a device that will add its own stream of packets to a set
> > it gets from elsewhere
> > - the classic case is an IP phone where there is a plug on the phone to
> > connect a PC.
> > - Pcs dont normally send tagged frames, and the 3 port bridge in the phone
> > doesnt have the horsepower to wrap a tag around every packet.
> > - but you want the phone traffic kept separate from PC (security, QoS and
> > so on).
>
> > So - pass the PC packet thru untagged, and tag the phone traffic.
> > At the switch the PC "stuff" is untagged and goes into the native VLAN,
> > phone traffic is tagged and goes into a different VLAN.
>
> > > TIA,
> > > st
>
> > --
> > Regards
>
> > stephen_h...@xyzworld.com - replace xyz with ntl
>
> Thanks,
> For "Some article say because of backward compatible with 802.3"
> they may think far end is Hub or switch/bridge which does not support
> 802.3,
> right?
> One more question, when a access port receive a untag frame, does it
> add
> a 802.1q tag or some other tag to make sure it can go same vlan inside
> of
> this switch?-

I have read something somewhere that stated that the Tags are
stripped off when frames enter the switch however clearly equivalent
information is carried 'with' the frame 'through' the switch.

So as far as we the Users are concerned I think that
you would have a good way of thinking about it if
you assumed that such a tag was used.

wrote:
> On 16 Apr, 05:31, aaabb...@hotmail.com wrote:
>> On 4ÔÂ15ÈÕ, ÏÂÎç1ʱ13·Ö, "stephen" <stephen_h...@xyzworld.com> wrote:
>>
>>
>>
>>
>>
>>> <aaabb...@hotmail.com> wrote in message
>>> news:123637df-5ec8-499a-a32c-...
>>>> A lot of people ask native vlan question.
>>>> I think using "vlan dot1q tag native" should eliminate this question.
>>>> at least for sw---sw connection. (all tagged just like isl)
>>>> I may not fully understand what's purpose why cisco make "native
>>>> vlan".
>>> cisco didnt invent this - it is part of 802.1Q.
>>>> Some article say because of backward compatible with 802.3.
>>> i suggest you try to find the standard and read around that,
>>> maybe start atwww.ieee.org
>>> AFAIR some of the standards docs are without charge for Ethernet.
>>>> Can anyone give an example?
>>> there are 2 Qs to think about.
>>> 1. set a port to be tagged
>>> - what do you do with a packet that arrives with no tag?
>>> the 2 common answers are to throw it away, or to put it into some sort of
>>> "default VLAN" - that is what untagged means for incoming packets.
>>> not putting a tag on outbound packets form that VLAN on that port allows 2
>>> way comms.
>>> this sounds silly - but it is what often needs to happen when you hook up an
>>> unconfigured device to set it up.
>>> 2. what happens when you want to split up 2 streams of packets on a port?
>>> sometimes you have a device that will add its own stream of packets to a set
>>> it gets from elsewhere
>>> - the classic case is an IP phone where there is a plug on the phone to
>>> connect a PC.
>>> - Pcs dont normally send tagged frames, and the 3 port bridge in the phone
>>> doesnt have the horsepower to wrap a tag around every packet.
>>> - but you want the phone traffic kept separate from PC (security, QoS and
>>> so on).
>>> So - pass the PC packet thru untagged, and tag the phone traffic.
>>> At the switch the PC "stuff" is untagged and goes into the native VLAN,
>>> phone traffic is tagged and goes into a different VLAN.
>>>> TIA,
>>>> st
>>> --
>>> Regards
>>> stephen_h...@xyzworld.com - replace xyz with ntl
>> Thanks,
>> For "Some article say because of backward compatible with 802.3"
>> they may think far end is Hub or switch/bridge which does not support
>> 802.3,
>> right?
>> One more question, when a access port receive a untag frame, does it
>> add
>> a 802.1q tag or some other tag to make sure it can go same vlan inside
>> of
>> this switch?-
>
> I have read something somewhere that stated that the Tags are
> stripped off when frames enter the switch however clearly equivalent
> information is carried 'with' the frame 'through' the switch.
>
> So as far as we the Users are concerned I think that
> you would have a good way of thinking about it if
> you assumed that such a tag was used.
>
>

When you configure a port-based VLAN on a switch, you are telling the
switch which ports are to be grouped into a common broadcast domain
(VLAN). Therefore when a switch receives a tagged frame on a trunk port,
it knows which ports it is permitted to forward too based on the
separation of broadcast domains (VLANs). Of course, if the switch has
learned the port that the destination host resides on, it will only
forward it out that port within the appropriate VLAN (assuming a unicast
packet). Broadcast packets may be flooded to all ports within a VLAN.

Best Regards,
News Reader

On 4ÔÂ16ÈÕ, ÉÏÎç6ʱ54·Ö, News Reader <u...@domain.null> wrote:
> Bo...@hotmail.co.uk wrote:
> > On 16 Apr, 05:31, aaabb...@hotmail.com wrote:
> >> On 4ÔÂ15ÈÕ, ÏÂÎç1ʱ13·Ö, "stephen" <stephen_h....@xyzworld.com> wrote:
>
> >>> <aaabb...@hotmail.com> wrote in message
> >>>news:123637df-5ec8-499a-a32c-....
> >>>> A lot of people ask native vlan question.
> >>>> I think using "vlan dot1q tag native" should eliminate this question.
> >>>> at least for sw---sw connection. (all tagged just like isl)
> >>>> I may not fully understand what's purpose why cisco make "native
> >>>> vlan".
> >>> cisco didnt invent this - it is part of 802.1Q.
> >>>> Some article say because of backward compatible with 802.3.
> >>> i suggest you try to find the standard and read around that,
> >>> maybe start atwww.ieee.org
> >>> AFAIR some of the standards docs are without charge for Ethernet.
> >>>> Can anyone give an example?
> >>> there are 2 Qs to think about.
> >>> 1. set a port to be tagged
> >>> - what do you do with a packet that arrives with no tag?
> >>> the 2 common answers are to throw it away, or to put it into some sort of
> >>> "default VLAN" - that is what untagged means for incoming packets.
> >>> not putting a tag on outbound packets form that VLAN on that port allows 2
> >>> way comms.
> >>> this sounds silly - but it is what often needs to happen when you hook up an
> >>> unconfigured device to set it up.
> >>> 2. what happens when you want to split up 2 streams of packets on a port?
> >>> sometimes you have a device that will add its own stream of packets to a set
> >>> it gets from elsewhere
> >>> - the classic case is an IP phone where there is a plug on the phone to
> >>> connect a PC.
> >>> - Pcs dont normally send tagged frames, and the 3 port bridge in the phone
> >>> doesnt have the horsepower to wrap a tag around every packet.
> >>> - but you want the phone traffic kept separate from PC (security, QoS and
> >>> so on).
> >>> So - pass the PC packet thru untagged, and tag the phone traffic.
> >>> At the switch the PC "stuff" is untagged and goes into the native VLAN,
> >>> phone traffic is tagged and goes into a different VLAN.
> >>>> TIA,
> >>>> st
> >>> --
> >>> Regards
> >>> stephen_h...@xyzworld.com - replace xyz with ntl
> >> Thanks,
> >> For "Some article say because of backward compatible with 802.3"
> >> they may think far end is Hub or switch/bridge which does not support
> >> 802.3,
> >> right?
> >> One more question, when a access port receive a untag frame, does it
> >> add
> >> a 802.1q tag or some other tag to make sure it can go same vlan inside
> >> of
> >> this switch?-
>
> > I have read something somewhere that stated that the Tags are
> > stripped off when frames enter the switch however clearly equivalent
> > information is carried 'with' the frame 'through' the switch.
>
> > So as far as we the Users are concerned I think that
> > you would have a good way of thinking about it if
> > you assumed that such a tag was used.
>
> When you configure a port-based VLAN on a switch, you are telling the
> switch which ports are to be grouped into a common broadcast domain
> (VLAN). Therefore when a switch receives a tagged frame on a trunk port,
> it knows which ports it is permitted to forward too based on the
> separation of broadcast domains (VLANs). Of course, if the switch has
> learned the port that the destination host resides on, it will only
> forward it out that port within the appropriate VLAN (assuming a unicast
> packet). Broadcast packets may be flooded to all ports within a VLAN.
>
> Best Regards,
> News Reader- Òþ²Ø±»ÒýÓÃÎÄ×Ö -
>
> - ÏÔʾÒýÓõÄÎÄ×Ö -

let me clear the second question up:
when a access port receive a untag frame from a
host, does it add a 802.1q tag or some other tag to make sure it can
go same vlan inside of switch?

wrote:
> On 4ÔÂ16ÈÕ, ÉÏÎç6ʱ54·Ö, News Reader <u...@domain.null> wrote:
>> Bo...@hotmail.co.uk wrote:
>>> On 16 Apr, 05:31, aaabb...@hotmail.com wrote:
>>>> On 4ÔÂ15ÈÕ, ÏÂÎç1ʱ13·Ö, "stephen" <stephen_h...@xyzworld.com> wrote:
>>>>> <aaabb...@hotmail.com> wrote in message
>>>>> news:123637df-5ec8-499a-a32c-...
>>>>>> A lot of people ask native vlan question.
>>>>>> I think using "vlan dot1q tag native" should eliminate this question.
>>>>>> at least for sw---sw connection. (all tagged just like isl)
>>>>>> I may not fully understand what's purpose why cisco make "native
>>>>>> vlan".
>>>>> cisco didnt invent this - it is part of 802.1Q.
>>>>>> Some article say because of backward compatible with 802.3.
>>>>> i suggest you try to find the standard and read around that,
>>>>> maybe start atwww.ieee.org
>>>>> AFAIR some of the standards docs are without charge for Ethernet.
>>>>>> Can anyone give an example?
>>>>> there are 2 Qs to think about.
>>>>> 1. set a port to be tagged
>>>>> - what do you do with a packet that arrives with no tag?
>>>>> the 2 common answers are to throw it away, or to put it into some sort of
>>>>> "default VLAN" - that is what untagged means for incoming packets.
>>>>> not putting a tag on outbound packets form that VLAN on that port allows 2
>>>>> way comms.
>>>>> this sounds silly - but it is what often needs to happen when you hook up an
>>>>> unconfigured device to set it up.
>>>>> 2. what happens when you want to split up 2 streams of packets on a port?
>>>>> sometimes you have a device that will add its own stream of packets to a set
>>>>> it gets from elsewhere
>>>>> - the classic case is an IP phone where there is a plug on the phone to
>>>>> connect a PC.
>>>>> - Pcs dont normally send tagged frames, and the 3 port bridge in the phone
>>>>> doesnt have the horsepower to wrap a tag around every packet.
>>>>> - but you want the phone traffic kept separate from PC (security, QoS and
>>>>> so on).
>>>>> So - pass the PC packet thru untagged, and tag the phone traffic.
>>>>> At the switch the PC "stuff" is untagged and goes into the native VLAN,
>>>>> phone traffic is tagged and goes into a different VLAN.
>>>>>> TIA,
>>>>>> st
>>>>> --
>>>>> Regards
>>>>> stephen_h...@xyzworld.com - replace xyz with ntl
>>>> Thanks,
>>>> For "Some article say because of backward compatible with 802.3"
>>>> they may think far end is Hub or switch/bridge which does not support
>>>> 802.3,
>>>> right?
>>>> One more question, when a access port receive a untag frame, does it
>>>> add
>>>> a 802.1q tag or some other tag to make sure it can go same vlan inside
>>>> of
>>>> this switch?-
>>> I have read something somewhere that stated that the Tags are
>>> stripped off when frames enter the switch however clearly equivalent
>>> information is carried 'with' the frame 'through' the switch.
>>> So as far as we the Users are concerned I think that
>>> you would have a good way of thinking about it if
>>> you assumed that such a tag was used.
>> When you configure a port-based VLAN on a switch, you are telling the
>> switch which ports are to be grouped into a common broadcast domain
>> (VLAN). Therefore when a switch receives a tagged frame on a trunk port,
>> it knows which ports it is permitted to forward too based on the
>> separation of broadcast domains (VLANs). Of course, if the switch has
>> learned the port that the destination host resides on, it will only
>> forward it out that port within the appropriate VLAN (assuming a unicast
>> packet). Broadcast packets may be flooded to all ports within a VLAN.
>>
>> Best Regards,
>> News Reader- Òþ²Ø±»ÒýÓÃÎÄ×Ö -
>>
>> - ÏÔʾÒýÓõÄÎÄ×Ö -
>
> let me clear the second question up:
> when a access port receive a untag frame from a
> host, does it add a 802.1q tag or some other tag to make sure it can
> go same vlan inside of switch?
>
>

I would "assume" that an untagged frame (the norm) sent by a host, and
received on a switch port that is assigned a non-native VLAN ID, would
get tagged at the ingress port; would remain so on its journey through
the switch, and get stripped on the egress port if the port was
configured for "access mode".

However, I would think that a programmer could (if desired) use some
other construct for segregating frames within the switch, and tag frames
as necessary as they egress onto a trunk port.

I think your answer is likely implementation dependent, and up to the
whims of the programmer.

Why get hung up on such an esoteric matter, when there are so many
practical issues to deal with?

Best Regards,
News Reader