I have a host setup for libvirt kvm/qemu vms. And I wonder a bit about
the overhead of the macvtap and how to configure the mtu's properly. To
be able to communicate with the host, I have moved the ip address of the
host from the adapter to a macvtap to allow host communication.
I have the below setup on hosts.
+---------+
| macvtap0|
+--| ip |
| | mtu1500 |
| +---------+
+---------+ | +---------+
|eth0.v100| | | macvtap1|
+--| no ip +-+--| ip |
+---------+ | | mtu1500 | | mtu1500 |
| eth0 | | +---------+ +---------+
| +--+
| mtu9000 | | +---------+
+---------+ | |eth0.v101|
+--| ip |
| mtu9000 |
+---------+
https://pastebin.com/9jJrMCTD
I can do a ping -M do -s 9000 between hosts via the vlan interface
eth0.v101. That is as expected.
The ping -M do -s 1500 macvtap0 and another host or macvtap1 fails. The
maximum size that does not fragment is 1472.
That is 28 bytes??? Where have they gone? I am only using macvtap, can
this be the combination of the parent interface being a vlan and that
macvtap is not properly handling this? Anyone experienced something
similar? Or can explain where these 28 bytes go?
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