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Citrix XenServer 7.1 LTSR CU2 Patch15 - Creating VMs with 16 Cores and more than 3 NICs

Tobias Hüpgen


Hello community,


we've got kinda nice problem with our Citrix XenServer 7.1 LTSR pool. We installed CU2 and patched it with the latest available patches. The pool is running on 3 Dell PowerEdge R740 Servers with supported hardware (2x Intel Gold 6144 CPUs - 2 Intel X710 NICs) - we checked the configuration in the Citrix HCL.


So. Let me tell you what's the problem:


If we create new VMs with 16 cores (Layout: 2 sockets - 8 CPUs / socket) with more than 3 NICs, the NICs 1-3 are working properly. All NICs more than 3 cannot startup in the Windows Guest OS - not important if we use Windows Server 2008R2, 2012R2, 2016 or 2019.


When we decrease the amount of cores to 14 or less - same layout - the NICs are working properly. After increasing to 16 cores again - the problem shows up again directly.


Do you guys have any idea what's the problem?


Find some screenshots of the device manager of one of the Windows Server 2016 VMs attached to this post.



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You are using Microsoft licensing (like Datacenter) that allows that many cores to be configured, right? If you try to add a VIF with the CLI vs. XenCEnter, does that make any difference? Are you sure the VIFs are just not showing up on XenCenter or how are you checking if they were correctly created or not? That all said, I think you should be able to create up to seven VIFs per VM. That is a strange result.

If you can't make headway, I'd suggest posting this as a possible bug on https://bugs.xenserver.org/



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Hello Tobias,


thank you for your advices. Fortunately the Citrix support sent me a Citrix article, which solved my problem (https://support.citrix.com/article/CTX255198)


After pasting " /opt/xensource/libexec/xen-cmdline --set-xen gnttab_max_frames=128 "  into the XenServer CLIs and rebooting the hosts, the problem doesn't arrive any longer.


I can now create VMs with more then 16 cores and up to 7 VIFs per VM.


Best regards,






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