Configuring Inter-VLAN Communication
Context
VLANIF interfaces are simple to configure and are one of the most commonly used technologies for inter-VLAN communication.
If a VLAN goes Down because all interfaces in the VLAN went Down, the system immediately reports the VLAN Down event to the corresponding VLANIF interface, instructing the VLANIF interface to go Down. To avoid network flapping from the VLANIF interface status change, enable VLAN damping on the VLANIF interface. With VLAN damping, after the last interface in Up state in a VLAN goes Down, the device starts a delay timer. It will only inform the corresponding VLANIF interface of the VLAN Down event after the timer expires. In this way, if an interface in the VLAN goes Up during the delay, the VLANIF interface remains Up.
The Maximum Transmission Unit (MTU) determines the maximum number of bytes that can be sent at a time. If the size of the packets exceeds the MTU supported by a receiver or a transit node, the packet will be fragmented or discarded, increasing the network transmission load. To avoid this problem, set the MTU of the VLANIF interface appropriately.
After configuring bandwidth for a VLANIF interface, you can use the NMS to query the bandwidth to facilitate traffic monitoring.
Pre-configuration Tasks
Before configuring inter-VLAN communication, complete the following tasks:
Assign VLANs.
- Configure the default gateway address of hosts as the IP address of the VLANIF interface.
Procedure
- Run system-view
The system view is displayed.
- Run interface vlanif vlan-id
The VLANIF interface view is displayed.
A VLANIF interface goes Up only when at least one physical interface in the corresponding VLAN is in Up state.
- (Optional) Run description description
The description of the VLANIF interface is configured.
- Run ip address ip-address { mask | mask-length } [ sub ]
An IP address is configured for the VLANIF interface to implement Layer 3 connectivity.
If IP addresses assigned to VLANIF interfaces belong to different network segments, you need to configure a routing protocol on the device to provide reachable routes.
Each VLANIF interface can be configured with one primary IP address and a maximum of 31 secondary IP addresses.
An IP address of a VLANIF interface can be statically configured or dynamically obtained using DHCP. For details about DHCP, see DHCP Configuration in the S2720, S5700, and S6700 V200R019C10 Configuration Guide - IP Services.
- (Optional) Run damping time delay-time
The delay of VLAN damping is set.
The value is in the range from 0 to 20, in seconds. By default, the delay is set to 0, which indicates that VLAN damping is disabled. - (Optional) Run mtu mtu
The MTU of the VLANIF interface is set.
By default, the value is 1500 bytes.
After using the mtu command to change the MTU of an interface, restart the interface to make the new MTU take effect. To restart the interface, run the shutdown command and then the undo shutdown command, or run the restart command in the interface view.
The MTU plus the Layer 2 frame header of a VLANIF interface must be smaller than the maximum frame length of the remote interface set by the jumboframe command; otherwise, some frames may be discarded.
Verifying the Configuration
Run the display interface vlanif [ vlan-id | main ] command to check the status, configuration, and traffic statistics of the VLANIF interface.
Only the VLANIF interface in Up state can forward packets at Layer 3. If the VLANIF interface goes Down, rectify the fault according to A VLANIF Interface Goes Down.