confusing about command "pinning max-links 1"

[a7_seven7]

Dear friends

i want to know the exact meaning of this command "pinning max-links 1" in a scenario. consider we want to configure port-channel and there is 4 link between nexus 5000 and nexus 2000. what is the diffrentce of configure "pinning max-links 4" compare to configure "pinning max-links 1". i want to know the diffrence action on connectivity if you set maximum 1 or set maximum 4?

[micturne]

Hello Seven,

Thanks for posting and welcome to the community.  One of our subject matter experts should be able to come up with an answer for you on this relatively quickly. 

-Mike

[franjime · Accepted solution]

Seven,

If you are connecting the Nexus 2000s to the Nexus 5000s using port-channels, you will want to set 'pinning max-links 1'.  If you have it set to another value, I believe the NX-OS will throw an error when configuring the port-channel.

This is a good document describing the connectivity options between Nexus 2000 and 5000:

http://www.cisco.com/en/US/prod/collateral/switches/ps9441/ps9670/C07-572829-01_Design_N5K_N2K_vPC_DG.pdf

Let us know if you need further clarification!

[a7_seven7]

tnx frank for your reply

[jj27]

If you are using a portchannel with 4 uplinks, you cannot control which link traffic will take.  The load-balancing algorithm configured on the portchannel will handle that for you.  In your case, pinning max-links 1 is acceptable. 

[a7_seven7]

tnx for your reply

[Devavrat Oka]

Too old to chime in... but it might help.

Pinning max-links <2-4> comes into play when you do static pinning. i.e. the FETs (fabric extender transceivers or links between 2K and parent switch) are not in a port-channel.

For a 48 port FEX:

pinning max-links 1 : 1 group of 48 hosts to 1 FET links

pinning max-links 2 : 2 groups of 24 hosts to 2 FET links

pinning max-links 3 : 3 groups of 18 hosts to 3 FET links

pinning max-links 4 : 4 groups of 12 hosts to 4 FET links

So, all 48 ports will be associated with 1 FET if 1 uplink is used and max-links is 1. So subscription ratio will be 48 * 1 gbps per 10 gbps uplink : 48:10 = 4.8:1

For max-links 2, subscription: 24:20 = 1.2:1

So, to sum it up, a good practice is to use a port-channel for a FEX uplink. A better option depending on whether you have a 5K or a 7K is to use a vPC as an uplink.

HTH,
Dev

[senatoredu]

pinning max-links 3 : 3 groups of 16 hosts to 3 FET link  (16 not 18)

nice explanation, this helped