NXOS mode : Is it Possible to Use the Nexus 9300 as the parent switch for Fex 2K Fex in the following Topology?

[S. B]

NXOS mode

Is it Possible to Use the Nexus 9300 as the parent switch of N2K fex, in the following Topology? (NXOS)

N5696Q is going to be EOS/EOL @ May 2021, and for keeping the DataCenter topology as it was , so it can be expanded with Nexus 9300 instead of Nexus5696Q (EOS in May 2021)

1. Is there any problems with this solution?
2. Does this Solution work Properly, same as it was working with N5k before.

Same as what Nexus 5K was the parent switch in the common classical Datacneter topologies (NXOS)

Architecture is :

Server to Fex = etherchannel , vPC

Fex to N5696Q = straight through connection (Etherchannel)

N5696Q to N7K = vPC

L2/L3 Boundry = N7K

Are there any important considerations that need to be taken?

For example, i found the 3 following considerations:(are there more?)

- Mostly Straight-Through connection between Fex and N9300 is required(No problem)

- Nexus 9300 only supports 16 x Fex (should be considered)

- FET cable is not supported between N2348UPQ and N9300 (should be considered)

[Sergiu.Daniluk]

Hi @S. B 

The N9K switches needs to be configured in a vPC domain - vpc peer-link is missing on the topology, so this is why I am mentioning (however for double-sided vpc between 9k and 7k you do need vpc, so i guess the existence of the vpc domain is implied)

Make sure you run a NXOS version which supports the FEXs. For example 9.3.1 for N9K-C93360YC-FX2 and 9.2.1 for the other two model. Reference: https://www.cisco.com/c/dam/en/us/td/docs/Website/datacenter/fexmatrix/fexmatrix.html 

- Mostly Straight-Through connection between Fex and N9300 is required(No problem) -> Only single homed FEXs are supported for your N9K switches.

Stay safe,

Sergiu

[S. B]

Dear @Sergiu.Daniluk 

Thanks

I edited the images.

I had forgotten to add the vpc links.

This is the correct diagram.

Does this solution work now?

Thanks 

[Sergiu.Daniluk]

Yes is supported.

Have a look over the supported topologies:

https://www.cisco.com/c/en/us/support/docs/switches/nexus-2000-series-fabric-extenders/200363-nexus-2000-fabric-extenders-supported-un.html 

Topology: Host VPC (Dual Links) and FEX Single Homed (Port Channel Mode) Straight through VPC Design

Stay safe,

Sergiu

[BastiiGee]

Two questions:

The n7ks are also configured as vpc peers, aren’t they?

Is it a problem to have the HSRP gateway connected with vpc?

[Sergiu.Daniluk]

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The n7ks are also configured as vpc peers, aren’t they?

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That's how it looks like from the topology image

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Is it a problem to have the HSRP gateway connected with vpc?

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Not at all. Quite on contrary, HSRP in combination with VPC makes both peer active in routing traffic. You just have to be aware of supported typologies and the requirements if you run dynamic routing protocols on Nexus switches: https://www.cisco.com/c/en/us/support/docs/ip/ip-routing/118997-technote-nexus-00.html 

Take care,

Sergiu

[BastiiGee]

Thanks for your answer.

in the vpc best practices guide it says:

A design where L3 device is vPC-attached to vPC domain and establishes L3 routing protocol peering adjacency with each peer device is not supported. Reason is traffic may be blackholed because of vPC loop avoidance (L3 ECMP decision and L2 port-channel hashing algorithms are running independently so traffic may need to cross vPC peer-link in order to reach the next L3 hop which is a vPC peer device).

So this means, that you shouldn’t connect a next hop routers or L3 device with a vpc. In the above case the next hop router would be 2 nexus switches which are also a vpc domain. ( but most of the pictures i found on the internet are showing 2 standalone nexus in the core layer without vpc domain peering , why? So between N5k and n7k also shouldn’t be a vpc but a l3 link only.

please correct me where I’m wrong.