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Beginner

Nexus FEX dualhome VPC

Hi I have 2 2248 FEXs dual-homed to 2 5548 parents which are VPC peers.

I understand that 1 port on a FEX must be configured on both parent switches in order to take affect.

What I want to know is that if a port channel is configured between ports on different FEXs which are dual-homed does it need to have the vPC command on the port channel as well? For example:

int eth101/1/1  (FEX 1)

channel-group 5 mode active

int eth102/1/1 (FEX 2)

channel-group 5 mode active

int port-channel 5

vpc 5?

If so, would the same apply if the port channel was configured on the same FEX? For example:

int eth101/1/1 (FEX 1)

channel-group 10 mode active

int eth101/1/2 (FEX 1)

channel-group 10 mode active

int port-channel 10

vpc 10?

Thanks,

Waqas

9 REPLIES 9
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Enthusiast

Hi Waqas;

With the help of vPC we can create a multi-chassis etherchannel.

If you have same device (ports on same FEX/Nexus switches) we don't required vPC, port will configured as simple port-channel.

int eth101/1/1
channel-group 10 mode active

int eth101/1/2
channel-group 10 mode active

int port-channel 10
no shut
switchport mode access/trunk

If your Server/Network devices connected to 2 FEX/Nexus switches and want to configure multi-chassis etherchannel then you need to configure port-channel with vPC.

int eth101/1/1
channel-group 5 mode active

int eth102/1/1
channel-group 5 mode active

int port-channel 5
no shut
switchport mode access/trunk
vpc 5

Thanks & Best regards;

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Thanks Ahmed,

What if I have the 2 FEXs dual homed? Would I still need the vpc command?

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Waqas,

Yes you still need the vpc command.

REgards

Inayath

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Hi there

in my opinion dual home is a lot more trouble that it give you in benefits, I have designed and installed Nexus at several companies and they have all decided to go single home in the end. Cisco support dual home, but if you press them they prefer single home as it's easier to deploy and support long term.

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Hi,

Would you mind sharing the details about what troubles you had with the dual home FEX?

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I have mixed feelings about dual-homing the FEXes.

The big disadvantage of single-homing is that if you lose a control plane, then you lose half of your server ports - so you better make sure that all your servers are port-channeled across FEXes.

The big disadvantage of dual-homing is that when you upgrade the firmware, all your FEXes get upgraded at the same time, so you lose the lot.  With single-homing you only lose half your server port (see above).

With dual-homing you better make sure your control planes have the same idea of the world.  That means carefully using WinMerge (or similar) from time to time to detect the differences.  Or use conf sync, but conf sync is so full of bugs that I have just given up on it after several years of use, and returned to conf t plus "stare and compare".

It's comes down to personal preference and design.

Kevin Dorrell

Luxembourg

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Thanks Kevin,

Would you be able to give me the steps required to change from a dual home to a single home topology?

I'm thinking I first disconnect the redundant connections and configure the ports on the parents to be as they should for a single home. Then re-connect the FEX to it's one parent.

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Sorry, could you check that please?  I have a lot of server port-channels between different FEXes that are themselves dual-homed, and I did not need to declare the vPCs.  The server vPCs get created by implication.  For example, vpc 10 in the original posting.

I only had to declare the vPC between the FEX uplinks for the dual-homed FEXes - vpc 5 in the original posting.

Kevn Dorrell

Luxembourg

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Thanks for mentioning this Kevin, I was thinking this was the case because it seems too redundant to configure VPC on a fex when they are already dual-homed using VPC.

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