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MTU considerations for iSCSI in VXLAN deployments


Userlevel 1
with the requirement of setting the mtu of VXLAN VNI's to 50 bytes smaller than the physical interface mtu. Should the mtu on the iSCSI initiator and targets be set to 8950 instead of 9000 ?

Are there any links to best practices or validated design guides for iSCSI in VXLAN deployments ?
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Best answer by Mark Horsfield 31 July 2018, 14:25

@Vikram A
I am cross-posting the same information (for others' benefit too) we provided you in the support case,

iSCSI is based on TCP, and you should configure the interface to 8950 (to accommodate the VXLAN header on an Ethernet segment).

You can use ping command to verify the max allowed MTU. the following command will set do-not-frag bit and specify payload to be 2000 bytes (so add packet headers to this number during your calculations)

code:
ping -M do 8.8.8.8 -s 2000
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Userlevel 4
Good question @Vikram A. We don't have best practices or design guides on iSCSI unfortunately. I'll ask about MTU setting and see what I hear back.
Userlevel 1
@Vikram A
I am cross-posting the same information (for others' benefit too) we provided you in the support case,

iSCSI is based on TCP, and you should configure the interface to 8950 (to accommodate the VXLAN header on an Ethernet segment).

You can use ping command to verify the max allowed MTU. the following command will set do-not-frag bit and specify payload to be 2000 bytes (so add packet headers to this number during your calculations)

code:
ping -M do 8.8.8.8 -s 2000
Userlevel 1
Thanks @Mark Horsfield . I am going to test this in my environment soon and post the findings here.

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