rfp and fpr interfaces not updated after changing network MTU

Bug #1823798 reported by Arjun Baindur on 2019-04-08
18
This bug affects 3 people
Affects Status Importance Assigned to Milestone
neutron
Medium
Brian Haley

Bug Description

I have a tenant network attached to a router and external network, and some VMs with Floating IPs deployed. I updated the network MTU from 1500 to 1300 (just as a test, but try any other MTU), and restarted nova compute, ovs agent, l3-agent.

All interfaces (qvo/qvb/qbr, qr, dhcp taps, sg, fg, qg) got updated except for the rfp-fpr peer link between qrouter and fip namespace:

[root@dvr-tn-vl-c7-10-4-211-218platform9 ~]# ifconfig | grep mtu
br-ex: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ens32: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ens34: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ens35: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ens34.1801: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
qbr05d85481-ca: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1300
qbr147c3499-25: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1300
qbrbf9399bf-17: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1300
qbrf1ba8ee0-e1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1300
qvb05d85481-ca: flags=4419<UP,BROADCAST,RUNNING,PROMISC,MULTICAST> mtu 1300
qvb147c3499-25: flags=4419<UP,BROADCAST,RUNNING,PROMISC,MULTICAST> mtu 1300
qvbbf9399bf-17: flags=4419<UP,BROADCAST,RUNNING,PROMISC,MULTICAST> mtu 1300
qvbf1ba8ee0-e1: flags=4419<UP,BROADCAST,RUNNING,PROMISC,MULTICAST> mtu 1300
qvo05d85481-ca: flags=4419<UP,BROADCAST,RUNNING,PROMISC,MULTICAST> mtu 1300
qvo147c3499-25: flags=4419<UP,BROADCAST,RUNNING,PROMISC,MULTICAST> mtu 1300
qvobf9399bf-17: flags=4419<UP,BROADCAST,RUNNING,PROMISC,MULTICAST> mtu 1300
qvof1ba8ee0-e1: flags=4419<UP,BROADCAST,RUNNING,PROMISC,MULTICAST> mtu 1300
tap05d85481-ca: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
tap147c3499-25: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
tapbf9399bf-17: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
tapf1ba8ee0-e1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
virbr0: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500
[root@dvr-tn-vl-c7-10-4-211-218platform9 ~]# ip netns exec qrouter-b57abb6d-92ff-4ebd-a71f-6b26646eddfa ifconfig | grep mtu
lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
qr-9f725d28-82: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1300
qr-a9852f10-d1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1300
rfp-b57abb6d-9: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
[root@dvr-tn-vl-c7-10-4-211-218platform9 ~]# ip netns exec qdhcp-ada1b967-9604-42ea-88bc-d887ce3e877e ifconfig | grep mtu
lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
tap8ecd0a51-63: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1300
[root@dvr-tn-vl-c7-10-4-211-218platform9 ~]# ip netns exec fip-4ff6386b-c547-465e-a734-49eed1ae6832 ifconfig | grep mtu
fg-a7668bc9-97: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1300
fpr-b57abb6d-9: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
[root@dvr-tn-vl-c7-10-4-211-218platform9 ~]# ip netns exec snat-b57abb6d-92ff-4ebd-a71f-6b26646eddfa ifconfig | grep mtu
lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
qg-d69632ce-e4: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1300
sg-83643ed0-34: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1300
sg-9eac9eee-69: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1300

VM taps are still at 1500, but will change if I powercycle VMs or migrate. rfp/fprs remain at 1500 and unsure of how to get their MTUs to update

Slawek Kaplonski (slaweq) wrote :

I tested this on devstack and indeed when I was changing MTU for private network, values on qr- ports in router's namespace were updated.
When I was changing MTU on public network, qg- port in snat- namespace was also updated properly.

But in both cases MTU on rfp- and fpr- ports were not changed.
IMO it should be changed accordingly to MTU change for public network but I would like confirmation for that from some L3 experts like Brian or LIU Yulong :)

Changed in neutron:
importance: Undecided → Medium
status: New → Confirmed

Fix proposed to branch: master
Review: https://review.openstack.org/651357

Changed in neutron:
assignee: nobody → Brian Haley (brian-haley)
status: Confirmed → In Progress

Reviewed: https://review.openstack.org/651357
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=6ded6d217adf61216fb10383d0150c966b92f11c
Submitter: Zuul
Branch: master

commit 6ded6d217adf61216fb10383d0150c966b92f11c
Author: Brian Haley <email address hidden>
Date: Tue Apr 9 15:08:32 2019 -0400

    DVR: Correctly change MTU in fip namespace

    The code that ensures the fpr/rfp veth pair exists
    between the qrouter and fip namespace was only setting
    the mtu of the devices if it had to create them. Set
    it all the time to support the mtu being changed.

    Change-Id: I176b5f4d4f12cf09f930e2c1944e98082a09bcc6
    Closes-bug: #1823798

Changed in neutron:
status: In Progress → Fix Released

Reviewed: https://review.openstack.org/652130
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=ee682138b908b82d5eeda3812a5cd47240312015
Submitter: Zuul
Branch: stable/stein

commit ee682138b908b82d5eeda3812a5cd47240312015
Author: Brian Haley <email address hidden>
Date: Tue Apr 9 15:08:32 2019 -0400

    DVR: Correctly change MTU in fip namespace

    The code that ensures the fpr/rfp veth pair exists
    between the qrouter and fip namespace was only setting
    the mtu of the devices if it had to create them. Set
    it all the time to support the mtu being changed.

    Change-Id: I176b5f4d4f12cf09f930e2c1944e98082a09bcc6
    Closes-bug: #1823798
    (cherry picked from commit 6ded6d217adf61216fb10383d0150c966b92f11c)

tags: added: in-stable-stein
tags: added: in-stable-pike

Reviewed: https://review.openstack.org/651979
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=3921ee7395aae5b9c13e03fe05d4177bb01665ee
Submitter: Zuul
Branch: stable/pike

commit 3921ee7395aae5b9c13e03fe05d4177bb01665ee
Author: Brian Haley <email address hidden>
Date: Tue Apr 9 15:08:32 2019 -0400

    DVR: Correctly change MTU in fip namespace

    The code that ensures the fpr/rfp veth pair exists
    between the qrouter and fip namespace was only setting
    the mtu of the devices if it had to create them. Set
    it all the time to support the mtu being changed.

    Change-Id: I176b5f4d4f12cf09f930e2c1944e98082a09bcc6
    Closes-bug: #1823798
    (cherry picked from commit 6ded6d217adf61216fb10383d0150c966b92f11c)

tags: added: in-stable-queens

Reviewed: https://review.openstack.org/651978
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=42a5a48c37400b0241f7792cf2ecb3cf630a1910
Submitter: Zuul
Branch: stable/queens

commit 42a5a48c37400b0241f7792cf2ecb3cf630a1910
Author: Brian Haley <email address hidden>
Date: Tue Apr 9 15:08:32 2019 -0400

    DVR: Correctly change MTU in fip namespace

    The code that ensures the fpr/rfp veth pair exists
    between the qrouter and fip namespace was only setting
    the mtu of the devices if it had to create them. Set
    it all the time to support the mtu being changed.

    Change-Id: I176b5f4d4f12cf09f930e2c1944e98082a09bcc6
    Closes-bug: #1823798
    (cherry picked from commit 6ded6d217adf61216fb10383d0150c966b92f11c)

tags: added: in-stable-rocky

Reviewed: https://review.openstack.org/651977
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=f71767bd02de048ac48e2aa59dc0fbf88bf2c1a1
Submitter: Zuul
Branch: stable/rocky

commit f71767bd02de048ac48e2aa59dc0fbf88bf2c1a1
Author: Brian Haley <email address hidden>
Date: Tue Apr 9 15:08:32 2019 -0400

    DVR: Correctly change MTU in fip namespace

    The code that ensures the fpr/rfp veth pair exists
    between the qrouter and fip namespace was only setting
    the mtu of the devices if it had to create them. Set
    it all the time to support the mtu being changed.

    Change-Id: I176b5f4d4f12cf09f930e2c1944e98082a09bcc6
    Closes-bug: #1823798
    (cherry picked from commit 6ded6d217adf61216fb10383d0150c966b92f11c)

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