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Category: Cisco UCS

The Cisco Unified Computing System (UCS) is a stateless computing environment which is gaining significant popularity in datacenters. UCS uses technology to abstract server specific settings from hardware into service profiles that comprise the identity of the server.

UCS Reserved VLANs

Anyone that has spent any time with Cisco equipment should just come to expect that there’s a number of VLANs that Cisco reserves for internal use. Cisco UCS is no exception. However, in UCS land, there’s a few curve balls you need to be aware of from version numbers and hardware types.

As I just completed an internal documentation of these VLAN IDs for our department, and since there’s a few places these are documented on Cisco’s web site, I felt it may make sense to just put them here for easy consumption later. In addition to the Cisco official documentation I’ve included my recommendations for reserving additional VLANs to make your life easier.

So, without further blabbering, here’s my current list of reserved VLANs on Cisco UCS, what they’re used for, and whether they can be changed or not..

Official Cisco UCS Port Reservations

VLAN IDDescriptionModifiable
3915-4042Only on Cisco UCS 6454 Fabric Interconnects
Used for internal system communication
See Cisco UCS Configuration Limits
Yes
4030-4047Used for internal system communication
See Cisco UCS Manager Network Management Guide
No
4048Cisco UCS 2.0 and later
Default VSAN’s FCoE VLAN ID
See Cisco UCS Manager Network Management Guide
Yes
4049Cisco UCS 2.0 and later
Default FCoE Storage Port Native VLAN ID
See Cisco UCS Manager Network Management Guide
Yes
4093Cisco UCS 4.0.1(c) and earlier
Used for internal system communication
See Cisco UCS Manager Network Management Guide
No
4094-4095Used for internal system communication
See Cisco UCS Manager Network Management Guide
No

My Bonus Recommended Reservations

Cisco UCS domains that are using Fibre Channel, whether by attaching to an existing Fibre Channel SAN fabric or by having an array directly connected to the Fabric Interconnect, will also require VLAN IDs for the VSANs within UCS. As I always design my storage fabrics as an A and B fabric I also create a separate VSAN ID for them (typically 11 and 12, respectively). Therefore, in my UCS domains I also create two VSANs and assign them unique VLAN IDs for the FCoE to run in.

VLAN IDVSAN IDDescription
321111Fibre Channel Fabric A
321212Fibre Channel Fabric B
321313Direct-Attached Array FI-A
321414Direct-Attached Array FI-B
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Booting ESXi in UEFI mode on Cisco UCS

Note: This process should work for Windows and Linux as well.  Verify the EFI boot path for the OS.

Through ESXi 6.0 I have run my hosts in Legacy BIOS mode on UCS.  There just was nothing significant enough worth the hassle of switching to UEFI on UCS (rather: I had more important fires to put out…).  The one feature I did want, Secure Boot, wasn’t supported by ESXi 6.0 and earlier.

vSphere 6.5 introduced support for Secure Boot.   Mike Foley has a great blog post about Secure Boot in ESXi 6.5.  If you are starting your 6.5 upgrade and are using Legacy mode, consider switching to UEFI.  It’s minimal effort and increases the security of your hypervisor.

Since I was working on rolling out a new UCS environment with ESXi 6.5 in a remote office environment, this felt like a great time to switch to UEFI and get the benefits of Secure Boot.  This is not complicated on UCS, but there is a new Boot Policy that must be created.  This policy can be reused for Windows (and other OS).

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