Note: This bug is displayed in read-only format because the product is no longer active in Red Hat Bugzilla.
The FDP team is no longer accepting new bugs in Bugzilla. Please report your issues under FDP project in Jira. Thanks.

Bug 2223046

Summary: Multichassis ports on localnet-attached logical switches should receive ICMP Path Discovery hints if their effective MTU is lower than localnet MTU
Product: Red Hat Enterprise Linux Fast Datapath Reporter: Mark Michelson <mmichels>
Component: ovn22.12Assignee: OVN Team <ovnteam>
Status: CLOSED ERRATA QA Contact: Ehsan Elahi <eelahi>
Severity: unspecified Docs Contact:
Priority: unspecified    
Version: FDP 23.BCC: ctrautma, jiji, jishi
Target Milestone: ---   
Target Release: ---   
Hardware: Unspecified   
OS: Unspecified   
Whiteboard:
Fixed In Version: ovn22.12-22.12.0-91.el9fdp Doc Type: If docs needed, set a value
Doc Text:
Story Points: ---
Clone Of: Environment:
Last Closed: 2023-08-21 02:08:18 UTC Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:

Description Mark Michelson 2023-07-15 00:44:23 UTC 
This bug was initially created as a copy of Bug #2180955

I am copying this bug because: 

The original issue is cited in an errata for fast datapath RHEL 8. This issue will be cited in an errata for fast datapath RHEL 9.

Description of problem:

When a port is multichassis (requested-chassis is a comma separated list), if the LS that the port belongs to has a localnet port, traffic to and from the multichassis port is tunneled anyway. (This is done to guarantee delivery of packets destined to the port MAC address to all its locations.)

This enforced tunneling may be a problem if the effective MTU for the ports becomes different from the theoretical MTU of the physical network that underlies the LS (defined by MTU of localnet port in the same switch). In this case, the port should not communicate with the outside world using the max MTU.

The proposal here is for OVN controller to set up ICMP Path Discovery replies to oversized packets received from a multichassis port, so that the port owner is aware of the change in circumstances and can adequately adjust their effective MTU.

The problem was originally discussed in ovs-dev ML: https://www.mail-archive.com/ovs-dev@openvswitch.org/msg68204.html

Implementation was proposed at: https://mail.openvswitch.org/pipermail/ovs-dev/2022-November/398981.html

This bug is to take the patch over and get it tested / merged in OVN.

The bug affects OSP live migration scenario for VMs attached to physical networks (=switches with localnet port).

I expect this bug to become a blocker for OSP 17.1 because of its effect on live migration scenario.
Comment 3 Ehsan Elahi 2023-08-01 08:38:21 UTC 
As per the reproducer mentioned in https://bugzilla.redhat.com/show_bug.cgi?id=2180955#c4

########## Verified on: ########

openvswitch-selinux-extra-policy-1.0-34.el9fdp.noarch
openvswitch2.17-2.17.0-95.el9fdp.x86_64
ovn22.12-22.12.0-91.el9fdp.x86_64
ovn22.12-central-22.12.0-91.el9fdp.x86_64
ovn22.12-host-22.12.0-91.el9fdp.x86_64
Comment 5 errata-xmlrpc 2023-08-21 02:08:18 UTC 
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory (ovn22.12 bug fix and enhancement update), and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2023:4677