Table of Contents

The FEX associate command is what designates this FEX as FEX 100 within the switch.
When a FEX is first recognized, it will likely need to download the
proper microcode from the 5000 or 7000 to which it is connected. This
process can take 10–15 minutes and will involve the FEX restarting.
There may be no indication of this happening, so either go get some
lunch or obsessively reenter the show fex command to see what’s going
on. You could do both, but make sure you don’t leave any crumbs in
the data center.
Pinning
Normally, with a 48-port 1 Gbps switch, assuming a 4×10 Gbps uplink EtherChannel
totaling 40 Gbps, the uplink will have a possible oversubscription ratio of 4.8:1. Pinning
allows us to assign banks of ports to individual uplinks instead of having all the ports
share a single EtherChannel. Why would we do this Read on.
Why is the ratio 4.8:1 and not 1.2:1 After all, there is a 40 Gbps uplink
and forty-eight 1 Gbps ports. The discrepancy is due to the nature of
EtherChannel load balancing. Remember, an EtherChannel is not really
a faster link, but rather multiple same-speed links balanced according
to a predefined algorithm. See Chapter 7 for more information on how
EtherChannel hashing works.
With four 10 Gbps uplinks, we can assign 12 ports to each 10 Gbps link, giving us an
oversubscription ratio of 1.2:1. That’s a potential four-to-one improvement in uplink
speed. Sounds like a great idea. The downside of this increase in usable uplink is that
should one of the uplinks fail, all 12 of the pinned ports will also be down. There is no
dynamic healing like there is with an EtherChannel when pinning fabric ports.
Pinning can be done with one, two, or four links. On a 48-port FEX, the breakdown is
as follows:
Pinning one
All host ports use one uplink. This is the method used with an EtherChannel
uplink.
Pinning two
The first 24 ports use the first link and the second 24 ports use the second uplink.
Pinning four
Each 12-port group uses its own uplink.
When using a FEX with all four uplinks bonded together, we must use a pinning of
one, configured within the FEX configuration block:
fex 101
pinning max-links 1
Nexus Design Features | 293