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Fixed upstream by:
commit 3bb87556b8ab010e5b808ac6775af7c10ea3d05d
Author: Laine Stump <laine>
Date: Tue Jan 12 14:10:05 2021 -0500
qemu: don't set interface MTU when managed='no'
v7.0.0-10-g3bb87556b8
Verified on:
ibvirt-daemon-7.3.0-1.el9.x86_64
qemu-kvm-6.0.0-4.el9.x86_64
Steps:
1.set the mtu of the interface to be smaller than the the pre-created tap device
mtu of the precreated device: 2000
mtu set in the interface: 1400
# ip tuntap add mode tap name mytap0
# ip l set dev mytap0 mtu 2000
# ip l show mytap0
53: mytap0: <BROADCAST,MULTICAST> mtu 2000 qdisc noop state DOWN mode DEFAULT group default qlen 1000
link/ether 46:fa:12:4f:33:be brd ff:ff:ff:ff:ff:ff
# virsh start avocado-vt-vm1
Domain 'avocado-vt-vm1' started
# virsh dumpxml avocado-vt-vm1 |grep /inter -B8
</controller>
<interface type='ethernet'>
<mac address='52:54:00:93:0f:bc'/>
<target dev='mytap0' managed='no'/>
<model type='virtio'/>
<mtu size='1400'/>
<alias name='net0'/>
<address type='pci' domain='0x0000' bus='0x01' slot='0x00' function='0x0'/>
</interface>
# ip l show mytap0
53: mytap0: <BROADCAST,MULTICAST> mtu 2000 qdisc noqueue state DOWN mode DEFAULT group default qlen 1000
link/ether 46:fa:12:4f:33:be brd ff:ff:ff:ff:ff:ff
# virsh console avocado-vt-vm1
Connected to domain 'avocado-vt-vm1'
Escape character is ^] (Ctrl + ])
nsstest login: root
Password:
Last login: Mon May 10 18:43:55 from 192.168.122.1
# ip l show enp1s0
2: enp1s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1400 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
link/ether 52:54:00:93:0f:bc brd ff:ff:ff:ff:ff:ff
2.set the mtu of the interface to be larger than the the pre-created tap device
mtu of the precreated device: 2000
mtu set in the interface: 3000
# virsh edit avocado-vt-vm1
<interface type='ethernet'>
<mac address='52:54:00:93:0f:bc'/>
<target dev='mytap0' managed='no'/>
<model type='virtio'/>
<mtu size='3000'/>
<alias name='net0'/>
<address type='pci' domain='0x0000' bus='0x01' slot='0x00' function='0x0'/>
</interface>
# virsh start avocado-vt-vm1
Domain 'avocado-vt-vm1' started
# ip l show mytap0
53: mytap0: <BROADCAST,MULTICAST> mtu 2000 qdisc noqueue state DOWN mode DEFAULT group default qlen 1000
link/ether 46:fa:12:4f:33:be brd ff:ff:ff:ff:ff:ff
# virsh console avocado-vt-vm1
Connected to domain 'avocado-vt-vm1'
Escape character is ^] (Ctrl + ])
nsstest login: root
Password:
Last login: Mon Jun 7 18:01:28 on ttyS0
[root@nsstest ~]# ip l show enp1s0
2: enp1s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 3000 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
link/ether 52:54:00:93:0f:bc brd ff:ff:ff:ff:ff:ff
Fixed upstream by: commit 3bb87556b8ab010e5b808ac6775af7c10ea3d05d Author: Laine Stump <laine> Date: Tue Jan 12 14:10:05 2021 -0500 qemu: don't set interface MTU when managed='no' v7.0.0-10-g3bb87556b8