Configuring an Interface to Insert the Actual MTU into DD Packets
Context
The default maximum transmission unit (MTU) is 0.
To improve compatibility with a non-Huawei device, an OSPF-enabled Huawei device adds the MTU 0 in DD packets to be sent and does not check the MTUs in received DD packets, allowing an OSPF neighbor relationship to be set up even if the two ends have different MTU settings.
However, under the default configuration, the non-Huawei device may discard an OSPF packet received from the Huawei device if the packet's actual MTU is greater than the MTU of the non-Huawei device. If the discarded packet is an LSU, an OSPF neighbor relationship can still be set up, but the route carried in the LSU fails to be learned, causing service interruptions.
To resolve this issue, run the ospf mtu-enable command to configure an interface to add the actual MTU in DD packets to be sent and check whether the MTU in a received DD packet is greater than the local MTU. If the interface MTU settings of the local and remote ends are different, an OSPF neighbor relationship cannot enter the Full state. In this manner, MTU inconsistency can then be identified in time.
Procedure
- Run system-view
The system view is displayed.
- Run interface interface-type interface-number
The OSPF interface view is displayed.
- (Optional) On an Ethernet interface, run undo portswitch
The interface is switched to Layer 3 mode.
By default, an Ethernet interface works in Layer 2 mode.
Only the S5720-EI, S5720-HI, S5730-HI, S5731-H, S5731-S, S5731S-H, S5731S-S, S5732-H, S6720-EI, S6720-HI, S6720S-EI, S6730-H, S6730S-H, S6730-S, and S6730S-S support switching between Layer 2 and Layer 3 modes.
- Run ospf mtu-enable
The interface is configured to insert the actual MTU into DD packets and check whether the MTU in DD packets from the neighbor exceeds the MTU of the local end.
By default, the MTU in DD packets sent by an interface is 0.
Performing this procedure causes the re-establishment of neighbor relationships.