[c-nsp] Nexus 5k dual sup design

[Ryan Rawdon]

On May 24, 2013, at 1:35 AM, Friedemann Stoyan wrote:

> On 23.05.13 22:15, Mike Hale wrote:
>> Ahhh, gotcha.
>> 
>> I've got no experience with that as of yet.  We're putting in 8 2248s
>> pretty shortly which I was going to dual-home for redundancy, but that
>> project is still in the early stages.  I'd also love to hear what
>> other folks have experienced with this kind of setup.
> 
> Dual Homed disadvantages
> 
> * the maximum number of FEX is halved
> * FCoE is not recommemded
>  http://www.cisco.com/en/US/docs/switches/datacenter/nexus5000/sw/mkt_ops_guides/513_n1_1/n5k_enhanced_vpc.html#wp1162674
> * welcome to config sync hell
> 
> We decide for straight through topology and it works like a charm.

We have ~10 2ks dual-homed to 5Ks in our datacenter.  An additional consideration is upgrades --

ISSU has very specific STP requirements, though those are not horrible to satisfy as long as you have additional switching infrastructure that can take over the root role during your upgrade window.  

Specific to the dual-homed design though:
- If you can't use ISSU, all of your FEXs will need to take a hit as they upgrade (sequentially, though I believe you can also whack them all at once)
- The FEXs can only do ISSU if the N5K parents are upgraded with ISSU
- If you can't tolerate downtime on the FEXs, do not install a layer 3 daughtercard into your 55xx (or do not home them to 55xx) , as you cannot use ISSU on them when they have layer 3 features in use.



> 
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