From: LoizosCisco (david_steven2001@yahoo.com)
Date: Wed Jun 02 2004 - 13:15:11 GMT-3
Alexei,
I have two Core 6509 and a dozen distribution 6509
MSFCs connecting to both cores. I have to configure
2GIG Etherchannel between the two cores and I am
wondering if I should configure etherchannel with
trunking (Layer 2), or Etherchannel with IP (Layer 3).
The connection between the cores and distribution
switches are Layer 3. Then there are multiple Layer 2
stacks below the Distribution which are trunked to the
distribution.
I am also concern about the VTP domain assignment. Do
I configure a VTP Server at each distribution layer
with the same domain name? What should be the best
practice for VTP assignment in suck an environment?
--- asadovnikov <asadovnikov@comcast.net> wrote:
> May I ask why do you need to interconnect the core
> switches in the first
> place?
>
> I know it sounds like silly question, but let us
> look into it... Let us say
> such link is not there... I would assume that all
> distribution switches
> have an uplink to each core.
>
> CORE-A CORE-B
> | \ __________/ |
> | \__/_______ |
> | / \ |
> | / \ |
> Distribution-A Distribution-B
>
> Say Distribution-A has a packet to ship to
> Distribution-B, and it sends it
> to CORE-A (for the sake of example). CORE-A would
> send it to Distribution-B
> directly.
>
> So when traffic hits one of the core switches it
> would not ever go to
> another core switch, except if there was a link
> failure. Further, if only
> one distribution to core link fails, all other
> distribution switches would
> use the core box which continues to have
> connectivity to this distribution
> switch.
>
>
> CORE-A CORE-B
> | __________/ |
> | / |
> | / |
> | / |
> Distribution-A Distribution-B
>
> In this case Distribution-A would know that the best
> route to Distribution-B
> is via CORE-B, and will forward all traffic there.
>
> So only possible need for one core to need to
> forward to another is in
> situation of dual link failures, like this
>
> CORE-A CORE-B
> | |
> | |
> | |
> | |
> Distribution-A Distribution-B
>
> Even then you have then another dozen or so
> distribution switches (not shown
> on the diagram above) which the cores can use to
> route around dual failure,
> even though it will introduce suboptimal routing.
>
> Much I hate any situations of suboptimal routing I
> have to ask what are the
> chances of your network to run with 2 hardware
> failures on the core. And my
> take would be that it is real low, as each failure
> on the core should be
> promptly fixed.
>
> Having said that you may want to interconnect the
> cores just in case, but
> then since we have just demonstrated that such link
> would be almost never
> used, oversubscription question is much irrelevant.
> If you want to be on
> really safe side by all means do provide core
> crosslink, but I would not
> sweat about how large it is... may be 2-4 gig (or if
> a lot of spare money do
> 2x 10 gig).
>
> Obviously each network requirements are so unique,
> it is almost impossible
> to have one-size-fits-all answers. So do send
> additional information.
>
> Best regards,
> Alexei
>
> P.S. QOS on the crosslinks/uplinks is a good think,
> assuming you have
> classification/marking on the edge and can actually
> tell what traffic is
> more or less important. For example if you provide
> voice services, and
> voice is marked on the network entry it is real good
> idea to give it
> priority over data, and with today hardware
> implementations of QOS there is
> no performance penalty to pay.
>
>
>
>
> -----Original Message-----
> From: nobody@groupstudy.com
> [mailto:nobody@groupstudy.com] On Behalf Of
> Kenneth Wygand
> Sent: Tuesday, June 01, 2004 11:48 AM
> To: Group Study
> Subject: Connecting two core switches / Design
>
>
> Hello all,
>
>
>
> I was thinking about large providers that need to
> connect core switches at
> very fast speeds. For example, say I have two 6506
> core switches I wanted to
> connect in the backbone. Say each one is
> terminating 20 - 30 fiber gigabit
> speed links. I would think it would be a poor idea
> to oversubscribe the
> link between these switches to a 1GBit or even
> 10GBit link. If the link was
> oversubscribed, logic would think that QoS should be
> employed here to make
> sure critical traffic (voice, video) gets through
> first, but all design
> guides point towards keeping all QoS out of the core
> to simply switch
> packets as fast as possible...
>
>
> What is recommended and is there any documentation /
> experience anyone can
> contribute?
>
>
>
> Thanks!
>
>
>
> Kenneth E. Wygand
> Systems Engineer, Project Services
>
> CISSP #37102, CCNP, CCDP, ACSP, Cisco IPT Design
> Specialist, MCP, CNA,
> Network+, A+
> Custom Computer Specialists, Inc.
>
> "I am not really smart. I just stick with problems
> longer." -Albert Einstein
>
>
>
> Custom Computer Specialists, Inc.
>
> "Celebrating 25 Years of Excellence"
>
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>
>
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