Archived from groups: comp.dcom.lans.ethernet (
More info?)
In article <111t52md8ef3sfa@news.supernews.com>,
sean <sean@snerts-r-us.org> writes:
>Manfred Kwiatkowski wrote:
>
>> In article <111n0g6gucqa1de@news.supernews.com>,
>> "T. Sean Weintz" <strap@hanh-ct.org> writes:
>>
>>>Manfred Kwiatkowski wrote:
>>>
>>>>In article <1MidnQA6RdSgzobfRVn-ow@speakeasy.net>,
>>>> Jonathan Sturges <nobody@nowhere.com> writes:
>>>>
>>>>
>>>>> ... Am I correct to assume that ports defined in
>>>>>an untagged VLAN are partitioned off from other ports, into their own
>>>>>broadcast domain? What will the switch do with packets destined for a
>>>>>host not in the untagged VLAN? Will it forward?
>>>>
>>>>
>>>>It will establish a VLAN correspondance for every packet and
>>>>then forward the packet accordingly.
>>>
>>>No. It will drop pacekets intended for other VLANS.
>>
>>
>> And what does this have to do with the untagged VLAN of a port?
>> There may be several tagged VLANs defined on this port.
>> In addition, forwarding of unknown VLANs may be set for this port.
>> Thus, "other" VLANs is totally meaningless in this context.
>
>Yes. My bad. He said ports defined in an untagged vlan. I thought he had
>said ports that were not tagged, implying they aren't also members of
>any tagged vlans. ...
This is probably what he thought he said.
But this comes from the term " untagged VLAN" that 3COM uses as
a port characteristic and thus makes people think that being
"untagged" is something special or even has a relation to the
"untaggedness" of other port. With 3COM, even the expression
"untagged VLAN of a port" ist misleading, as the SuperStack
allows port mebership as tagged and untagged at the same time (sic!)
> ... Some switches don't allow that anyway (my baystack
>450's are a good example of a fairly common non-low end switch that fits
>that description) - port must be tagged member of all vlans it belongs
>to or an untagged member of all vlans it belongs to. Can't be tagged on
>one vlan it is a member of and not tagged on another. I was always
>taught it's a bad idea to do that anyway - tagging is for trunking, and
>both end should be either all tagged or all untagged. Mixing makes it
>confusing.
Not at all. Confusing are the brain damaged configuration options
and restrictions of most switches as well as implicit definitions.
Some switches only allow trunk xor access as your 450, some even
force the default VLAN on trunks, some only allow the default VLAN
untagged and some only allow configuration via the default vlan.
>
>>>(That's sort of the whole point of VLANS)
>Never understood why so many also use it for prioritizing when diffserv
>is so much more flexible (at least it is on my nortel and netgear stuff)
You can use any bit in a packet the way you like if both sides
of the link (are able to) interpret it in similar ways.
--
Manfred Kwiatkowski kwiatkowski@zrz.tu-berlin.de