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Posted by vicky on June 30, 2008, 3:01 am
On Jun 30, 12:42=A0am, rober...@hushmail.com (Walter Roberson) wrote:
> In article <fe9d0880-d249-44f8-af4f-75ff7b1a5...@w5g2000prd.googlegroups.c=
om>,
>
> > =A0 =A0is there is a necessity of route field in layer 2 switch ...
> > =A0 =A0 =A0 =A0please tell me ...
>
> No, there is no necessity for that.
>
> For example, it is possible to build a layer 2 switch in which every
> port has a dedicated "send" path to each other port (e.g., the wiring
> to send from port B to port D is completely different than the wiring
> used to send from port C to port D); and when a packet came in to a
> port, the port could send the packet literally simultaneously to
> every other port, and then each output port could discard the
> packets that are not destined for that output port. No routing
> information of any kind would have to be kept on such a layer 2
> switch, as each output port would independantly decide whether
> the output packet was to be transmitted or not.
>
> I am not saying that this would be a *good* way to build a
> layer 2 switch, but your question was about whether there is
> a *necessity* of having some kind of "route fiele", and my example
> above demonstrates that it is not *necessary*.
>
> Now, it could potentially be much more *efficient* to have some kind
> of "route field" in real layer 2 switches -- but it is not *necessary>
>
> Note, by the way, that in networking, the word "route" usually
> refers to layer 3 information. Unmanaged layer 2 switches do not need
> to hold any layer 3 information for basic layer 2 operations, so
> if you are referring to "route" in the layer 3 sense, then the
> answer is a flat NO. My answer about the hypothetical layer 2
> switch was for the case where you might have meant "route field"
> more generally, such as some kind of internal table that listed
> MAC addresses and their associated port: my example shows that
> even that kind of internal table is not *necessary* in a layer 2 switch.
>
> You have been asking a lot of questions about VLANs lately, and
> one of your questions that I answered recently but which you did not
> understand (or believe?) my answer gave a scenario in which you
> were attempting to show that layer 2 switch must have
> an intra-vlan router in order to provide VLAN connectivity in single-
> instance STP cases. I suspect that your current question is just
> a rephrasing of that earlier question, and I will reinforce my
> answer of that time: if you use a layer 2 switch with VLANs that
> are restricted to particular ports, and you use a single-instance STP
> protocol, then your VLAN connectivity *will* break, and the breaking
> would be the fault of the person that configured the situation,
> not the fault of the layer 2 switch. Furthermore, there is no
> requirement that layer 2 switches support VLANs *at all*.
>
> Several times, I have noticed you get confused about the functionality
> that *must* be supported in -all- layer 2 switches, mixing it up
> with functionality that needs only to be supported in layer 2 switches
> that claim to have standard conformance to particular -optional-
> features.
----------------------------------------------------------------------------=
Thanks a lot sir,
for ur wonderful reply, again i m thank ful
to u that u noticing my queries ,
Sir according to ur reply i've something to ask .... may i....plz
As u mentioned here about inter-vlan route and one of my query is
related to that .....
so the functionality of inter-valn route is provided in l2 switch is
only if the switch controller provide some inter-vlan supporting
register support
or is done without that.
and route field info ia necessary in case of IGMP Snooping ,,, sir wat
u say about this....
please ....
Thanks
Vikrant
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