In the past, the MTU of libvirt virtual network bridge devices was implicitly set by setting the MTU of the "dummy tap device" (which was being added in order to force a particular MAC address from the bridge). But the dummy tap device was removed in commit ee6c936fbb (libvirt-6.8.0), and so the mtu setting in the network is ignored. The solution is, of course, to explicitly set the bridge device MTU when it is created. Note that any guest interface with a larger MTU that is attached will cause the bridge to (temporarily) assume the larger MTU, but it will revert to the bridge's own MTU when that device is deleted (this is not due to anything libvirt does; it's just how Linux host bridges work). Resolves: https://bugzilla.redhat.com/1913561 Signed-off-by: Laine Stump <laine@xxxxxxxxxx> ee6c936fbbo-set-mtu Signed-off-by: Laine Stump <laine@xxxxxxxxxx> --- src/network/bridge_driver.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/src/network/bridge_driver.c b/src/network/bridge_driver.c index b7c604eaea..519a473995 100644 --- a/src/network/bridge_driver.c +++ b/src/network/bridge_driver.c @@ -2336,6 +2336,9 @@ networkStartNetworkVirtual(virNetworkDriverStatePtr driver, /* Set bridge options */ + if (def->mtu && virNetDevSetMTU(def->bridge, def->mtu) < 0) + goto error; + /* delay is configured in seconds, but virNetDevBridgeSetSTPDelay * expects milliseconds */ -- 2.29.2
