Previous software versions allowed configuration of VLAN IP addresses in overlapping subnets which can cause incorrect routing of packets and result in IP communication failure. As of software version WB.15.09, overlapping subnet configurations are no longer allowed. An overlapping subnet is determined by the configuration order. The subnet that is configured first is valid, but any subsequent IP addresses that overlap are not allowed.
When the switch is booted into software version WB.15.09 or later, and the configuration file includes overlapping subnets, the following occurs:
The event log provides an error message in the format:
ip: VLANx : IP initialization failed for vlan x.
For a multinetted VLAN (multiple IP addresses assigned to the VLAN), only the IP addresses that are overlapping subnets are removed. The other IP addresses on the VLAN are retained and function correctly. The error message can be somewhat misleading; the IP addresses on the VLAN that are not overlapping are initialized correctly.
The output of the
show ip command correctly indicates that the overlapping IP address does not exist on the VLANs that have error messages in the event log.
The output of the
show running-config command incorrectly indicates that the overlapping IP address is configured. In
Figure 48: An IP address that is not actually configured on the VLAN, the IP address shown in VLAN6 is not actually configured on the VLAN; it has been removed.
Figure 48: An IP address that is not actually configured on the VLAN
switch(config)# show running-config
.
.
.
vlan 5
name “VLAN5”
ip address 11.22.33.1 255.0.0.0
exit
vlan 6
name “VLAN6”
ip address 11.23.34.1 255.255.255.0
exit
The information is retained in the config file to allow you to boot up the switch and have it function as it did when it was configured with earlier software that allows overlapping subnets.If you attempt to remove the overlapping subnet from the VLAN, the switch displays an error message similar to:
The IP address <ip-address> is not configured on this VLAN
This occurs because the overlapping IP address has been removed and is not visible to the switch. To resolve this:
Enter the
show ip command to determine which addresses are visible to the switch.
Remove the erroneous IP addresses from the config file by entering the
no ip address command to remove all the IP addresses from the specific VLAN. Be sure to document the other valid IP addresses on that VLAN so they can be restored after removing the erroneous IP addresses from the config file.
If you go back to a software version prior to WB.15.09 before removing the overlapping IP address, the prior software version enables the overlapping IP subnet.