Connecting a Switch to a 2232 FEX

[visitor68]

It is my understanding that the host ports on the FEXs can only have servers connected to them and not switch uplinks - like, say, from a blade switch. The reason, as I understand it, is that the host ports are hard-coded for PortFast and cannot be changed. So, of course you would never connect a dot1q inter-switch link to a port configured for PortFast. You can, but its certainly not recommended for obvious reasons.

But is that the ONLY reason?

[Amit Singh]

You cannot connect a full blown switch with STP running on a FEX-Port.

Please could you provide us with the TAC case number where TAC engineer has suggested that you can connect a switch running BPDU to a FEX port. I would like to talk to the TAC engineer and get his views on this.

Flex link is a L2 technology where you can use a L2 port as a back up of another one and you do not run STP on the ports configured as Flex-Links on the switch.

http://www.cisco.com/en/US/docs/switches/lan/catalyst3750x_3560x/software/release/12.2_53_se/configuration/guide/swflink.html

Hope this helps.

Cheers,

-amit singh

[visitor68]

Yes, I remember now what Flex Links are. I cant use them for  2 reasons:

1. The downstream switch that I want to connect to the FEX is a non-Cisco switch.

2. The links will be connecting to a vPC domain, and I dont wan to lose the active/active capability.

As far as the account team for this client and the TAC person we dealt with, let me get back to you on that.

Thanks

[Aleksandar Aleksiev]

Hi,

Since you are going to use the vPC domain, your non-Cisco switch will use port aggregation (i.e. LACP) for his uplinks to the FEX.

This is loop-free architecture and you don't need STP at all. It can be completely disabled of BPDU filtered (depending from the switch features).

From this perspective the non-Cisco switch will never send BPDU to the FEX and the err-disable protection will never be trigered.

Probably that's the Cisco TAC eng. viewpoint...

Greets,

Alex

[thomp]

Hi Amit,  Old thread but should there be any issue if you want to connect a switch to the FEX using a L3 point to point VPC  

[ekhoo]

Hi Amit and Jerry,

Need your input on Router connected to N2k. I understand the N2K is design for end host connection rather then connect to other downstream switch which may cause some issue as Jerry and you mention on above post.

Do you see any issue connecting a router such as Cisco 3900 to N2K? I am getting two conflicting information from below two post.

https://supportforums.cisco.com/thread/2165943

https://supportforums.cisco.com/thread/2133188

[Leo Laohoo]

BPDU Guard is PERMANENTLY enabled by default on a FEX port.

The only way you can connect a switch to a FEX port is to DISABLE STP on the port of switch (used as the uplink to the FEX).