Bug 1753470

Summary:	MTU too small for Geneve on vsphere
Product:	OpenShift Container Platform	Reporter:	zhaozhanqi <zzhao>
Component:	Networking	Assignee:	Abhinav Dahiya <adahiya>
Networking sub component:	ovn-kubernetes	QA Contact:	Johnny Liu <jialiu>
Status:	CLOSED NOTABUG	Docs Contact:
Severity:	urgent
Priority:	urgent	CC:	bbreard, cdc, dustymabe, imcleod, jcallen, jligon, nstielau
Version:	4.2.0	Keywords:	TestBlocker
Target Milestone:	---
Target Release:	4.2.0
Hardware:	All
OS:	All
Whiteboard:
Fixed In Version:		Doc Type:	If docs needed, set a value
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2019-09-19 16:30:12 UTC	Type:	Bug
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description zhaozhanqi 2019-09-19 03:07:49 UTC

Description of problem:
hi, from bug https://bugzilla.redhat.com/show_bug.cgi?id=1750606#c19 

for now the default nic MTU is 1500 in vsphere coreos image. Can we update the default MTU to 1600 or more.  since the Geneve Requires configuring transport networks with an MTU size of at least 1600 bytes 


Version-Release number of selected component (if applicable):
Red Hat Enterprise Linux CoreOS 42.80.20190916.0
4.18.0-80.11.1.el8_0.x86_64

How reproducible:
always

Steps to Reproduce:
1. setup cluster with OVN network type on vsphere
2.
3.

Actual results:
The cluster cannot be setup 


Expected results:


Additional info:

Comment 1 zhaozhanqi 2019-09-19 03:11:44 UTC

hi, can we build a new coreos image for vsphere with default MTU is 1600 to have a try. 

since this block our OVN installation. thanks

Comment 2 Casey Callendrello 2019-09-19 13:05:31 UTC

I'm not sure this is the issue. 1500 should be the correct MTU.

Comment 3 Micah Abbott 2019-09-19 14:37:13 UTC

Based on the linked comment from BZ#1750606, Geneve requires an MTU of 1600 or greater.  See the docs:

https://docs.vmware.com/en/VMware-Validated-Design/4.3/com.vmware.vvd.sddc-nsxt-design.doc/GUID-3FF2471C-665B-4E84-8DE4-ED3F35A58DE8.html

If we were to change this from the default of 1500, there is likely larger implications for installing OCP/RHCOS when *not* using OVN/Geneve.


I spoke with Joe Callen about this and he recommended that we use Terraform via the Installer to configure the MTU when using OVN on vSphere.

Re-assigning to Installer.

Comment 4 Abhinav Dahiya 2019-09-19 14:58:06 UTC

Networking is the responsibility of network operator. It's the one that setups and enabled ovn for cluster, it should be the one making those modifications.

Comment 5 Casey Callendrello 2019-09-19 16:30:12 UTC

We don't need 1600 MTU. Sorry for the noise.