Nexus 2000 FEX connected to a Cisco 2800 Router

[wayne.hubener]

I've read that FEX is designed for Host connections, will FEX support a Cisco 2811 Router connection?

[Oleksandr Nesterov]

Hi Wayne.

Technicaly it can be connected, but Do NOT extend the downstream device topology, because downstream devices will suffer from FEX buffer limitation. As you correctly mentioned - it was designed as top-rack switch for connecting hosts.

HTH,

Alex

[ekhoo]

Hi Alex,

Could you please explain what do you mean by  "Do NOT extend the downstream device topology".

Could you please point me to some doco or links as well? we were planning to connect a wan router to n2k recently until I saw this post.

Regards,

Sean

[Keny Perez]

Hi,

Nexus 2K were designed to work as a extension of a parent Switch, either a N5K or N7K.  These parent switches will fully manage those FEXs (Fabric Extenders) in the sense that even if you configure a port, that is done accessing the parent switch, or even when doing a software upgrade.

The FEXs are seeing as a virtual expansion of the parent switch.

When N2K are used with N5k/7k, you are taking advantage of a ToR (Top of Rack) solution and EoR (End of Row) at the same time, minimizing the cabling for host to the N2k and from the N2K to the 5k/7k.

I have never seen anyone using a 2k attached to something different then a 5k/7k, and that made me wonder and search, which took me to:

http://www.cisco.com/en/US/prod/collateral/switches/ps9441/ps10110/data_sheet_c78-507093.html (table 2)

That shows that not only is compatible with the 7k/5k but also with the 6k´s, but definitely, I saw nothing about any other device being compatible.

I hope that helps.

-Kenny

[ekhoo]

Kenny. thanks for your reply.

We do have N7K and N2K in our data centre with ToR setup to minimize cabling and patch panel to server racks. however, one of our racks have Cisco 3900 WAN router and few ASA firewalls. The dilemma I have now is how to connect back those routers and firewall to our data centre switch.

I have N2K FEX on top of our rack where I could just connect those routers and firewalls devices.

However based on few discussion posts and info I got, it seem like the right way to do it is to run a patch panel and connect those routers and firewalls directly to N7K  instead of N2K FEX.

I noticed Alex said N2K FEX may suffer from buffer issue if i were to connect router to FEX. However, traffic from our wan router is less than 100M and much less than our server which has 10G connections. In addition, the new N2K-E switches have better buffer capacity.

I would like to find out more info why connecting router or other WAN devices (excluding switch) to N2K FEX is not recommended.

regards,

Sean Khoo

[Keny Perez]

Sean,

I see that more like a desing matter, with a design attached, I do not see how you may use your WAN router to the access layer, in regards to the ASAs, I see them better at the distribution (you may have a great desgin in mind)

-Kenny

[Asim Pandey]

I feel the question remains unanswered.

Sean's question is based on Alex's answer that "Do NOT extend the downstream device topology, because downstream devices will suffer from FEX buffer limitation"

I have the same question?

question is pretty straightforward.

Can i connect a WAN router like an MPLS-CE router to a FEX port?

This FEX (2248 or 2232) can be part of access layer connected to a NX-5548UP.

Is this not a recommended design, and if not, why?

I know that FEX ports are best suited for servers/hosts.

Are the FEX ports not designed to be connected to a WAN router or a Firewall as compared to the native NX-5548UP port?

[Tim Heckmann]

Hi Asim,

Technically nothing stops you from connecting a WAN router to a FEX port. However - as kenperez already mentioned - having the WAN router in the access layer is not a design you would normally choose. In most cases there is a lot of traffic coming from and going to a WAN router. All this traffic then needs to go to and come from the parent switch. So you might have a bottleneck on the FEX port buffer. Also, (depending on your design) this could potentially lead to a high utilization of the FEX uplink.

I hope this answers your question.

-Tim