Missing PMTUD for ingress traffic
| Affects | Status | Importance | Assigned to | Milestone | |
|---|---|---|---|---|---|
| ovn (Ubuntu) |
Fix Released
|
High
|
Unassigned | ||
| Focal |
Triaged
|
High
|
Unassigned | ||
| Hirsute |
Won't Fix
|
High
|
Unassigned | ||
| Impish |
Fix Released
|
High
|
Unassigned | ||
| Jammy |
Fix Released
|
High
|
Unassigned | ||
Bug Description
According to this bug[0] and these patches[1][2][3] the support to emit a ICMP "need to fragment" packet was added in ovn-21.09, Wallaby UCA carries ovn-20.12
This limitation becomes a problem when the overlay network is configured to use jumbo frames and the external network uses a MTU of 1500 .
[Environment]
Focal Wallaby with a dedicated ovn-chassis application to act as gateway
ovn-chassis-gw:
bindings:
? ''
: oam-space
data: overlay-space
charm: cs:ovn-
options:
source: cloud:focal-
bridge-
ovn-
prefer-
num_units: 2
to:
- 1001
- 1002
[0] https:/
[1] https:/
[2] https:/
[3] https:/
| Frode Nordahl (fnordahl) wrote | #1 |
| summary: |
- Missing PPMTUD for ICMP and UDP when there are dedicated gateways + Missing PMTUD for ingress traffic |
| Changed in ovn (Ubuntu): | |
| status: | New → Triaged |
| importance: | Undecided → High |
| Changed in ovn (Ubuntu Hirsute): | |
| status: | New → Triaged |
| importance: | Undecided → High |
| Changed in ovn (Ubuntu Focal): | |
| status: | New → Triaged |
| importance: | Undecided → High |
| Changed in ovn (Ubuntu Jammy): | |
| status: | Triaged → Fix Released |
| Changed in ovn (Ubuntu Impish): | |
| status: | New → Fix Released |
| importance: | Undecided → High |
| Brian Murray (brian-murray) wrote | #2 |
| Changed in ovn (Ubuntu Hirsute): | |
| status: | Triaged → Won't Fix |
Thank you for raising this issue, so just to confirm, OVN 20.03 already does send ICMP type 3 (Destination Unreachable) code 4 (Fragmentation needed and DF was set) [4] to instances in the cloud, informing the client of the gateway MTU when the `gateway_mtu` flag is set on the LRP.
So the issue you are describing would only come into play if there are machines connected directly to the provider network using a MTU > the OVN LR MTU and/or a external to openstack router has MTU > the OVN LR MTU on its L3 interface facing the provider network?
4: https:/