350-401 Hot Standby Router Protocol (HSRP) Practice Question
A company has a requirement to provide redundancy for the default gateway on a subnet. Two switches are configured with HSRP. Which requirement must be met for the interfaces on the switches to form the HSRP group?
⚠ Common exam trap
A common misconception is that HSRP interfaces must be Layer 2 switchports. In reality, HSRP requires Layer 3 interfaces (SVIs or routed ports) that are in the same VLAN to exchange multicast hellos and maintain the virtual IP and MAC address.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The interfaces must be in the same VLAN.
HSRP is a First Hop Redundancy Protocol that provides a virtual gateway for hosts. To form an HSRP group, the participating interfaces must be Layer 3 interfaces (either SVIs on switches or routed ports on multilayer switches) that are configured with IP addresses and belong to the same VLAN. Option B is incorrect because HSRP does not run on Layer 2 switchports; those ports do not have IP addresses and cannot send HSRP messages. Option D is correct because being in the same VLAN ensures the switches share the same broadcast domain, allowing HSRP multicast hello messages to reach each other.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The interfaces must be on the same physical switch.
Why it's wrong here
HSRP is intentionally designed for two separate physical switches to provide gateway redundancy, such as in an access-distribution or distribution-core topology. The protocol relies on Layer 2 multicast, which only requires a trunk or VLAN that spans both devices; the physical chassis is irrelevant. As long as the VLAN is allowed on the inter-switch link, the two interfaces can be on different switches and form an HSRP group. Requiring the same physical switch is therefore incorrect and would undermine the device-level redundancy HSRP is meant to provide.
- ✗
The interfaces must be Layer 2 switchports.
Why it's wrong here
HSRP operates at Layer 3 because it requires an interface with an IP address and the capability to route frames; a Layer 2 switchport is purely a frame-forwarding port with no IP configuration. On a multilayer switch, HSRP is enabled on an SVI (VLAN interface) or a routed port, both of which are Layer 3 constructs. A Layer 2 switchport simply forwards Ethernet frames to the local VLAN and cannot run the HSRP election or own a virtual IP. Therefore, this option is incorrect.
- ✗
The interfaces must have the same IP address.
Why it's wrong here
Each HSRP participant must have its own unique real IP address in the same subnet to source hello packets and identify itself during the election process. The shared virtual IP is a service address configured with the standby command, and it is not used as the source IP in hello messages—each router uses its real IP instead. If both interfaces were assigned the same IP, an address conflict would occur, breaking routing and ARP. Thus, the interfaces need different real IPs plus one common virtual IP.
- ✓
The interfaces must be in the same VLAN.
Why this is correct
HSRP requires all participants to be in the same Layer 2 broadcast domain because hello messages are multicast onto the local VLAN. The multicast destination is 224.0.0.2 (HSRPv1) or 224.0.0.102 (HSRPv2) with a TTL of 1; if the interfaces reside in different VLANs, the broadcast domains are isolated, so the hellos never reach the peer and no HSRP adjacency forms. The virtual IP must also belong to the same IP subnet as the real interface IPs, and that subnet maps to exactly one VLAN; different VLANs imply different subnets and break the redundant gateway function.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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