200-150 · Question #151
In HSRP, how do interfaces determine failure and assign standby and active routers?
The correct answer is A. by using multicast UDP hello messages. HSRP routers detect active/standby roles and interface failures by exchanging multicast UDP hello messages on a well-known group address.
Question
In HSRP, how do interfaces determine failure and assign standby and active routers?
Options
- Aby using multicast UDP hello messages
- Bby using Cisco Discovery Protocol
- Cby exchanging BPDUs
- Dby using Spanning Tree Protocol
How the community answered
(50 responses)- A90% (45)
- B2% (1)
- C6% (3)
- D2% (1)
Why each option
HSRP routers detect active/standby roles and interface failures by exchanging multicast UDP hello messages on a well-known group address.
HSRP routers send hello messages every 3 seconds by default to the multicast address 224.0.0.2 (HSRPv1) or 224.0.0.102 (HSRPv2) using UDP port 1985.
Cisco Discovery Protocol is a Layer 2 neighbor discovery protocol and plays no role in HSRP failure detection or role election.
BPDUs are Bridge Protocol Data Units used exclusively by Spanning Tree Protocol to prevent Layer 2 loops, not by HSRP.
Spanning Tree Protocol operates at Layer 2 to prevent switching loops and has no mechanism for gateway redundancy or HSRP role assignment.
Concept tested: HSRP hello mechanism and failure detection
Source: https://www.cisco.com/c/en/us/support/docs/ip/hot-standby-router-protocol-hsrp/9234-hsrpguidetoc.html
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