Assigning VLANs and/or subnets to each area

After you define an OSPF area (page A-25), you can assign one or more VLANs and/or subnets to it. When a VLAN is assigned to an area, all currently configured IP addresses in that VLAN are automatically included in the assignment unless you enter a specific IP address.

NOTE:

All static VLANs configured on a routing switch configured for OSPF must be assigned to one of the defined areas in the AS.

Syntax: 


vlan vid # ip ospf [ip-addr | all] area ospf-area-id

Executed in a specific VLAN context to assign the VLAN or individual subnets in the VLAN to the specified area. Requires that the area is already configured on the routing switch (page A-25.)

When executed without specifying an IP address or using the all keyword, this command assigns all configured networks in the VLAN to the specified OSPF area.

vlan vid

Defines the VLAN context for executing the area assignment.

ip-addr

Defines a specific subnet on the VLAN to assign to a configured OSPF area.

all

Assigns all subnets configured on the VLAN to a configured OSPF area.

area ospf-area-id

Identifies the OSPF area to which the VLAN or selected subnet should be assigned.

NOTE:
If you add a new subnet IP address to a VLAN after assigning the VLAN to an OSPF area, you must also assign the new subnet to an area:

  • If all subnets in the VLAN should be assigned to the same area, just execute

    ip ospf area ospf-area-id

    .

  • But if different subnets belong in different areas, you must explicitly assign the new subnet to the desired area.

Also, to assign a VLAN to an OSPF area, the VLAN must be configured with at least one IP address. Otherwise, executing this command results in the following CLI message:

OSPF can not be configured on this VLAN.

Example

To assign VLAN 8 on a routing switch to area 3 and include all IP addresses configured in the VLAN, enter the following commands:

switch(ospf)# vlan 8
switch(vlan-8)# ip ospf area 3
Suppose that a system operator wants to assign the three subnets configured in VLAN 10 as shown below:

  • 10.10.10.1 to OSPF area 5

  • 10.10.11.1 to OSPF area 5

  • 10.10.12.1 to OSPF area 6

The operator could use the following commands to configure the above assignments:

switch(ospf)# vlan 10
switch(vlan-10)# ip ospf 10.10.10.1 area 5
switch(vlan-10)# ip ospf 10.10.11.1 area 5
switch(vlan-10)# ip ospf 10.10.12.1 area 6