Bug 1908775 - MTU is not set correctly for IPsec case
Summary: MTU is not set correctly for IPsec case
Alias: None
Product: OpenShift Container Platform
Classification: Red Hat
Component: Networking
Version: 4.7
Hardware: Unspecified
OS: Unspecified
Target Milestone: ---
: 4.7.0
Assignee: Mark Gray
QA Contact: Anurag saxena
Depends On:
TreeView+ depends on / blocked
Reported: 2020-12-17 15:15 UTC by Mark Gray
Modified: 2021-02-08 17:18 UTC (History)
4 users (show)

Fixed In Version:
Doc Type: No Doc Update
Doc Text:
Clone Of:
Last Closed: 2021-02-08 17:18:09 UTC
Target Upstream Version:

Attachments (Terms of Use)

System ID Private Priority Status Summary Last Updated
Github openshift cluster-network-operator pull 928 0 None closed Bug 1908775: ovn-ipsec: Adjust MTU to account for additional ESP overhead 2021-02-08 16:05:06 UTC

Description Mark Gray 2020-12-17 15:15:40 UTC
Description of problem:

MTU should be adjusted when IPsec is enabled to account for packet overhead of adding IPsec headers.

Version-Release number of selected component (if applicable): OCP 4.7

How reproducible:

Steps to Reproduce:
1. Start cluster with IPsec disabled
2. Create Pod
3. Run `ip l | grep mtu` in pod to view MTU
4. Start cluster with IPsec enabled
5. Create Pod
6. Run `ip l | grep mtu` in pod to view MTU

Actual results:
* MTUs are the same value

Expected results:
* MTU with IPsec enabled should be adjusted to account for IPsec header

Additional info:

Comment 1 Anurag saxena 2020-12-17 15:31:38 UTC
@mark.d.gray Whats the ipsec mtu overhead supposed to be?

Comment 3 Mark Gray 2020-12-18 15:58:06 UTC
@anusaxen: The overhead is 46B at a maximum.

Comment 8 Mark Gray 2021-01-04 18:00:14 UTC
(In reply to Ke Wang from comment #6)
> Per doc
> https://access.redhat.com/documentation/en-us/openshift_container_platform/3.
> 11/html/cluster_administration/admin-guide-ipsec, the ipsec overhead is 62B.

The overhead of IPsec depends on the IPsec mode (transport or tunnel) and the encryption algorithm used. I am unsure how it was configured in 3.11 but it may have been using different parameters. For 4.7, it should have a maximum overhead of 46B. The motivation for this is described in the commit message of the PR.

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