Nexus 5548 Collapsed Core

[de1denta]

Hi,

I'm looking at deploying 2 x 5548 switches with L3 modules as a collapsed core for a small data centre. The switches will connect to storage and VMware hosts as well as upstream MPLS routers and firewalls.

I will need to create a L2 trunk between the 5548 switches to provide L2 mobility for the virtual enviroment but I'm also looking at implemeting an EIGRP for upstream routing.

Question, is it ok to use L2 trunk and SVIs to provide adjacency between the 5548s or is adding a dedicated L3 point to point link recommended for routing? I assume that the L3 and L2 links can run in parallel?

Thanks,

[Reza Sharifi · Accepted solution]

Hi,

For redundancy, you need to run VPC between the 2 5Ks using 2 10Gig links.  VPC makes both devices logically look like one. Also, if you are planning to run EIGRP, between the 2 devices, than you need a 3rd link for routing only.

Have a look at these 2 documents:

http://www.cisco.com/en/US/prod/collateral/switches/ps9441/ps9670/design_guide_c07-625857.pdf

http://bradhedlund.com/2010/12/16/routing-over-nexus-7000-vpc-peer-link-yes-and-no/

HTH

[de1denta]

Hi,

This is very helpful, thank you.

I forgot to mention in my original post that one the upstream MPLS routers is using subinterfaces (required for WAAS) so I will need to configure L2 trunks between this router and 5548 swithes (using backup active/standby interfaces on the router for resiliency, interface backup command) My topology is similar to picture 2 in Brad Hedlund's post but without no VPC to the upstream switch/router

Am I correct in saying that in this instance the MPLS router will be try and maintain an EIGRP adjacency to both 5548 switches over its active link and the VPC peer link which is not supported? So installing a dedicated link for routing between the 5548s will be required?

Thanks,

[Reza Sharifi]

That is correct. A link for just layer 3 connection is required.  Also, we had a great discussion regarding VPC, layer-2 link later-3 link, etc.. on Nexus series not too long ago.

https://supportforums.cisco.com/thread/2101574?start=0&tstart=0

HTH

[de1denta]

Thats great.

One last question, can the L3 connection be used for the vpc keep alive link as well?

Thanks,

Will

[Reza Sharifi]

No, if I remember correctly, it is only for layer-3.

Reza

[de1denta]

Ok. Well the 5548s are going to be the only switches in the data centre so I wont have an external switch to connect my management interfaces for the keepalive link. Can the managment interfaces be connected back-to-back with a crossover cable for the keepalive link? The 5548s will be managed inband so loosing the oob management is not a problem

Thanks

[Oleksandr Nesterov · Accepted solution]

Hi Will

Yes - it's possible.

But such solution is highly not recommended.

You can buy some cheap switch and connect management ports to it. And perform n5k management and keep-alive link through it.

Otherwise if you will connect ports back-to-back and traffic storm will occur in your network - only way to deal with it will be to physicaly reach devices, disconnect keep-alive and than continue with troubleshooting.

HTH,

Alex.

[de1denta]

Hi Alex,

We dont have out of band management in our network so if we had a traffic storm then we wouldnt be able to connect to the switches anyway.

The 5548 switches will have the L3 modules installed and will be providing a small core for our network, a dedicated SVI will be configured for inband management. I assume that in this case a back-to-back keepalive link wont have a negitive impact on our network.