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> This is what I wanted to hear.
> Anyway, that document leaves me a bit puzzled ...
> at first it says: use a L3 link between distribution switches, don't
> use a L2 link because keeping in sync HSRP and STP for different VLANs
> is tedious and error prone. Then it goes on showing a config with HSRP
> + L3 link + STP root.


No, this is what you want to hear
That's my view anyway.



Access1
/ \
/ \
L2 / \ L2
/ \
/ \
/ \
/ L3 \
Dist1-----------------Dist2
\ /
\ /
\ /
L2 \ / L2
\ /
\ /
\ /
Access2

No STP needed, no unicast flooding due to HSRP
and asymetric routing. Never been there done that
however thats the one I like the looks of.

Each VLAN is constrained to only one access switch
although each Access switch can support more then one
VLAN if trunking or multiple parallel uplinks are used.

WHat you say in text and what you draw is different. By not allowing
VLAN trunks to exist beyond the distribs (which means you aren't using
VTP) you essentially divide you network into multiple L2s topologies.

For one VLAN you have
> Access1
> / \
> / \
> L2 / \ L2
> / \
> / \
> / \
> / L3 \
> Dist1-----------------Dist2

and for another VLAN you have this
> Dist1-----------------Dist2
> \ /
> \ /
> \ /
> L2 \ / L2
> \ /
> \ /
> \ /
> Access2

It is up to you to ensure you never misconfigure any vlan or trunk to
allow the diagram you drew to exist. That's why people run STP. One
misconfigured trunk or vlan and you've just taken out your network.

Secondly, are you saying you won't be running HSRP?
If you run HSRP You still have issues with who talks to which router.
If an Access2 device uses a router on DIST1 and an Access1 device uses
a router on DIST2 you wil get assymetric routing and promot unicast
flooding. DIST1 will know about access1 and DIST2 will know about
access 2.


Also if you have hybrid DISTs which many allow devices on DIST1 will
pass throught Access1 to reach DISt2 within the same VLAN.

wrote:

>No, this is what you want to hear
>That's my view anyway.
>
>
>
> Access1
> / \
> / \
> L2 / \ L2
> / \
> / \
> / \
> / L3 \
> Dist1-----------------Dist2
> \ /
> \ /
> \ /
> L2 \ / L2
> \ /
> \ /
> \ /
> Access2
>
>No STP needed, no unicast flooding due to HSRP
>and asymetric routing. Never been there done that
>however thats the one I like the looks of.
>
>Each VLAN is constrained to only one access switch
>although each Access switch can support more then one
>VLAN if trunking or multiple parallel uplinks are used.

DiGiTAL_ViNYL (no email)

Since one PPT slide is worth 1000 words, I read "Campus Network
Multilayer Architecture and Design Guidelines", which you can find here
and probably already know very well:

http://www.cisco.com/en/US/netsol/ns...s_package.html

Slide 67 says that with "Layer3 distribution interconnection" you have
"no spanning tree" and "all links (are) active". The slide shows what
seems a "best case scenario" with VLANs not spanning more than one
switch each. There is no mention of STP roots. Note that in the
previous slide, showing a Layer2 interconnection, a STP root is
explicitly configured.

Slide 87 on the other hand shows what looks the very same
configuration, with a "Layer3 distribution interconnection" and VLANs
not spanning more than one switch each, but in this case it suggests to
do "STP root and HSRP primary tuning".

Kate0... said
> Slide 87 on the other hand shows what looks the very same
> configuration, with a "Layer3 distribution interconnection" and VLANs
> not spanning more than one switch each, but in this case it suggests to
> do "STP root and HSRP primary tuning".

Well, even Cisco arn't perfect. Clearly a missprint

Slide 87 has no need of STP for it to function "as designed".

I think that I read those slides a while back and became a convert
Bye bye L2 loops, hello wire speed L3:--)))


I agree that it is probably best to leave STP on.

I think that the proposed design will be (almost) free of
unicast flooding.
The only L2 device in the network that needs to know
the mac address of an access-layer connected PC (say)
is directly connected to that very PC and therefore will
almost always know it's MAC/port relationship.

[zephyrus]

Dear all.

I design a campus Lan like in the PIC that I attached.
My question is : Do we have Loop in it or not?

In CCNP switch book,it said that,if we use HSRP in Dis. switches, STP always be Converge in layer 2 (access switches),WHY?!!

Tanx.

Image : http://www.mediafire.com/?4n41nwtigp0j5jq