mak14
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MTU 9000

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Dear Community,

i set vmkernel 9000 and vDS standard switch 1500 and Physical switch set to 9000 is this configuration supported or it will create network issues

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a_p_
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The MTU needs to be configured from end to end, i.e. also in the vSwitch.
You can test whether MTU 9000 works using the vmkping command from one of the ESXi hosts.

vmkping -I vmk# -d -s 8972 <target-ip>

André

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IRIX201110141
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YES... it will cause problem because the VMK try to use a packet size up to 9k but it will blocked or need to defragmented.

If you have CEIP enabled the VMware Advisor within vCenter will raise an alarm also about mismatched MTU settings.

Regards,
Joerg

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a_p_
Leadership
Leadership

The MTU needs to be configured from end to end, i.e. also in the vSwitch.
You can test whether MTU 9000 works using the vmkping command from one of the ESXi hosts.

vmkping -I vmk# -d -s 8972 <target-ip>

André

mak14
Enthusiast
Enthusiast

Yes, i agree

but if I configure vmkernel and physical adapter as MTU 9000 and vSwitch as MTU 1500. will it cause communication problems?

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IRIX201110141
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YES... it will cause problem because the VMK try to use a packet size up to 9k but it will blocked or need to defragmented.

If you have CEIP enabled the VMware Advisor within vCenter will raise an alarm also about mismatched MTU settings.

Regards,
Joerg

mak14
Enthusiast
Enthusiast

But for below configuration
configure vmkernel and physical adapter as MTU 9000 and vSwitch as MTU 1500.

Does vSwitch does de-fragmentation or simply it will fail to send frames. 

When i was migrating standard switch to Distributed switch. Accidently DS switch MTU was set to 1500 and When i migrated vSAN VM kernel i lost connection and VMs were shut down. i was trying to figure out is it because of MTU 1500? 

logs
2022-09-12T12:05:12.655Z cpu2:3987430)Uplink: 5942: vmnic4: TSO packet has large MSS (8948) plus L7 offset (66), which can't be fit into MTU (1500)
2022-09-12T12:05:12.655Z cpu0:3987430)Uplink: 5942: vmnic4: TSO packet has large MSS (8948) plus L7 offset (66), which can't be fit into MTU (1500)
2022-09-12T12:05:12.655Z cpu0:3987430)Uplink: 5976: vmnic4: Non TSO L2 payload size exceeds uplink MTU. FrameLen: 3134, L3 header offset: 14

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