A customer is running out of IP addresses in a network segment. What will happen if they add an additional IP subnet to the same VLAN?

Question

Options

• AThis would result in a single SVI using two subinterfaces
• BUsers can reach each other and establish PTP traffic without passing an L3 point in the same
• CBroadcasts for the two subnets will arrive on all ports in the same VLAN
• DIGMP will not work in both of the subnets in the same VLAN

• A
  2% (1)
• B
  4% (2)
• C
  85% (41)
• D
  8% (4)

Explanation

Adding a second IP subnet to the same VLAN extends the IP address space, but both subnets still share the same Layer 2 broadcast domain. Because a VLAN is the broadcast domain, any broadcast packet - ARP requests, DHCP discoveries, etc. - generated by either subnet floods every port in that VLAN. This is the defining behavior of L2 broadcast domains and is exactly what C describes.

Why the distractors are wrong:

• A is wrong because SVIs are single L3 interfaces per VLAN on a switch; subinterfaces apply to physical router ports (router-on-a-stick), not SVIs. A second subnet doesn't split an SVI into subinterfaces.
• B is wrong because hosts in different subnets must always pass through an L3 device (router or L3 switch) to reach each other - even if they're on the same VLAN. Same VLAN ≠ same subnet.
• D is wrong because IGMP functionality is not inherently broken by having two subnets in a VLAN. IGMP snooping operates at L2 and continues to work normally regardless of subnet count.

Memory tip: A VLAN is a single room - everyone in the room hears every announcement. Subnets are seating sections within that room; they limit who talks to whom at L3, but the loudspeaker (broadcast) still reaches every seat.

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