I have created 3 VLANS which should not overlap but somehow are giving me overlapping problems. Any reasons why? Is the switch buggy?

VLAN 10 Usable: to

VLAN 20 Usable: to

VLAN 30 Usable: to

Switch(config-if)#int vlan10
Switch(config-if)#ip address
Switch(config-if)#int vlan 20
Switch(config-if)#ip address
Switch(config-if)#int vlan 30
Switch(config-if)#ip address
% overlaps with Vlan20
  • See the excellent answers to this question for how to calculate subnets and prefixes. Also, "VLSM" is an obsolete term from the classful networking era more than thirty years ago - it's called CIDR since.
    – Zac67
    Mar 5 at 18:03

1 Answer 1


The subnet that belongs to is, which overlaps with VLAN 20. It doesn't magically start at .24 just because you want it to.

  • I will need to use VLSM subnetting chart for this, correct?
    – Xavier Lim
    Mar 5 at 20:12
  • See the comment above to your question and follow that link. You can use a chart or calculator -- up to you.
    – Ron Trunk
    Mar 5 at 20:34

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