KB.15.15

Example 39 Tagged and untagged VLAN technology in the same network

VLAN Operating Rules

Disabled overlapping subnet

configuration

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 K.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 K.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. For example, in the following output, the

IP address shown in VLAN6 is not actually configured

on the VLAN; it has been removed.

Introducing tagged VLAN technology into networks running untagged VLANs 47