Data Domain: Invalid MTU Causes VLAN Interface Failure After Reboot

Data Domain becomes inaccessible following a reboot or interface down/up operation.
VLAN interface status shows as down or disabled.
Attempting to configure an MTU larger than the parent interface MTU returns a validation error.
The interface may continue running with the previously configured MTU until a reboot or interface restart occurs.
After reboot, the affected VLAN interface fails to come up.

# net config veth1.100 mtu 9000

Configuring interface... **** vlan mtu, 9000, is bigger than the base, veth1, mtu, 1500 

!!!! juno-193 YOUR DATA IS IN DANGER !!!! # reg_cmd show config_master.net | grep veth1

config_master.net.veth1.100.bonding.mode = dontcare

config_master.net.veth1.100.enabled = true

config_master.net.veth1.100.mtu_state = 1

config_master.net.veth1.100.mtusize = 9000

veth1.100   yes       running   no     7.7.7.7                                     255.255.255.0     n/a                                   connected
                                       xxxx::xxxx:xxxx:fe8e:e47c**                  /64

!!!! juno-193 YOUR DATA IS IN DANGER !!!! # reboot 

Broadcast message from root (pts/0) : The system is going down for reboot NOW!

!!!! juno-193 YOUR DATA IS IN DANGER !!!! # 
veth1       yes       running   no     9.9.9.9                                     255.255.255.0     n/a    roundrobin: eth3a,eth3b        connected
                                       xxxx:xxxx:xxxx:xxxx:ac0:ebff:fe8e:e47c**    /64
                                       xxxx::xxxx:xxxx:fe8e:e47c**                  /64
                                       xxxx:xxxx:xxxx:bea5:ac0:ebff:fe8e:e47c**    /64
veth1.100   yes       down      no     7.7.7.7                                     255.255.255.0     n/a                                   disabled

When an invalid MTU value is configured on a VLAN interface associated with a bonded interface, the system correctly rejects the configuration and continues operating with the previously configured MTU. 
However, the invalid MTU value is still written to the registry and is not reverted.
During a reboot, or when the interface is brought down and back up, the system reads the persisted configuration from the registry and attempts to apply the invalid MTU. 
Since the MTU validation fails during interface initialization, the VLAN interface is unable to come online.
Even though the MTU configuration failed, the invalid value remains stored and is reapplied on subsequent interface initialization events.

If the issue has already occurred:
Access the system through iDRAC, serial console, or another out-of-band management method.
Configure a valid MTU value that does not exceed the MTU of the parent interface.
Bring the interface back online if required.

Example:

net config veth1.100 mtu 1500

Preventative Action
Until a permanent fix is available, whenever an MTU configuration attempt fails validation, immediately rerun the command using a valid MTU value.

Engineering is planning a fix for DDOS 8.8 

Example:

net config veth1.100 mtu 9000

Configuring interface...**** vlan mtu, 9000, is bigger than the base, veth1, mtu, 1500

Correct it immediately:

net config veth1.100 mtu 1500

This ensures the registry is updated with a valid value and prevents the interface from failing after a reboot or interface restart.
Important Notes

Systems without iDRAC or other remote management access may require a Customer Engineer (CE) onsite visit to access the serial console and correct the MTU configuration.
On newer systems, if network connectivity is lost and no alternative management path exists, onsite intervention may also be required to restore access.