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Community Member

Nexus 5K L3 Design (Best Practice)

Hi All,

I have a few questions regarding the L3 capabilities of the 5548UPs.
We have the enterprise licensing with the L3 Daughter card and want to route from our 4500-X VSS' to our Nexus 5548s running version: 6.0(2)N2(3)
Our design is that our data center traffic is kept isolated in the DC. Our users will route across the 4500Xs to the DC to access the server host.

What we have is 4 physical links from our VSS stack to our Nexus cluster, with 2 cables from VSS1 to N5K-1 and 2 cables from VSS2 to N5K-2. See below:

VSS1 ---------------- 2 x --------------N5K-1
    |                                                    |
    |                                                    |
VS Link                                     PeerLink
    |                                                    |
    |                                                    |
 VSS2 ----------------2 x ---------------N5K-2

What we also have in our topology is an IPS between the VSS and Nexus switches to complicate the design.

Talking to my Sales Engineer he suggested putting the 4 links in a VPC using SVIs at each end and HSRP. Looking further into this it seems that this is a supported design but not a recommended design. I believe this works for Unicast forwarding but doesn't work for multicast according to this doc which is for version 5.1.3.

From what I read, I believe the recommended way is to use point to Point routed links (/30s) x 4 and use ECMP to load balance the traffic.  

The other thing I am looking into is finding out whether the IPS units allow asymmetric routing, eg if it comes in on port 1, and goes out on port 4, will it understand the flows? I'm waiting to hear back on this.

Would this assumption be correct to use the Point to Poink /30s and use ECMP? Is this what I should be doing rather than the SVIs across a vPC?

Do I need to have a separate L3 links between the N5K's?

Is there any other considerations I should be making?

Community Member

Just had an update on the IPS

Just had an update on the IPS units - they support asymetric routing, which is good news.

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