Cisco CCNA Preparation · lesson 22 of 36 · 25 min
The Problem FHRP Solves
End devices are configured with a single default gateway IP. If that gateway router fails, all hosts on the subnet lose connectivity — even if a backup router exists. First Hop Redundancy Protocols (FHRPs) solve this by presenting a virtual IP address as the default gateway. Multiple physical routers share this virtual IP; if the active router fails, another takes over transparently.
HSRP — Hot Standby Router Protocol
HSRP is a Cisco proprietary FHRP. One router is elected Active (forwards traffic for the virtual IP), another is Standby (monitors the Active and takes over if it fails). All other HSRP routers are in the Listen state.
Hosts configure the virtual IP as their default gateway. The Active router also uses a virtual MAC address (0000.0C07.ACxx where xx = group number in hex).
HSRP failover sequence
VRRP — Virtual Router Redundancy Protocol
VRRP (RFC 5798) is the open-standard equivalent of HSRP. Key differences: the Master router (not Active) forwards traffic; the virtual MAC is 0000.5E00.01xx; the Master can also be the IP address owner (the router whose real IP equals the virtual IP).
GLBP — Gateway Load Balancing Protocol
GLBP is Cisco proprietary and goes beyond HSRP/VRRP by providing load balancing across multiple gateways simultaneously. All routers in the GLBP group can forward traffic — each is assigned a different virtual MAC address. The AVG (Active Virtual Gateway) assigns virtual MACs to hosts via ARP replies.
HSRP and VRRP waste the standby router’s bandwidth — it sits idle. GLBP uses all routers actively.
Knowledge Check — 10 Questions
First Hop Redundancy
What problem do FHRPs solve?
- Routing loops
- Single point of failure at the default gateway
- Slow convergence in OSPF
- IP address exhaustion
Answer: Single point of failure at the default gateway
If a host’s single default gateway fails, it loses connectivity. FHRPs present a virtual IP shared by multiple routers — if one fails, another takes over transparently.
In HSRP, which router responds to ARP requests for the virtual IP?
- All routers in the group
- The Standby router
- The Active router
- The router with the highest IP
Answer: The Active router
The HSRP Active router owns the virtual IP and virtual MAC. It responds to ARP requests and forwards all traffic for the virtual IP.
What is the default HSRP priority?
- 50
- 100
- 110
- 255
Answer: 100
Default HSRP priority is 100. The router with the highest priority becomes Active. Tie is broken by highest interface IP address.
What does HSRP preemption do?
- Increases the Hello timer
- Allows a higher-priority router to reclaim the Active role after recovering from a failure
- Enables load balancing
- Disables the Standby router
Answer: Allows a higher-priority router to reclaim the Active role after recovering from a failure
Without preemption, a recovered higher-priority router stays in Standby. With standby [group] preempt, it reclaims the Active role automatically.
What is the virtual MAC address format for HSRP group 1?
- 0000.5E00.0101
- 0000.0C07.AC01
- 0000.0C07.AC00
- 0000.5E00.0001
Answer: 0000.0C07.AC01
HSRP virtual MAC = 0000.0C07.ACxx where xx is the group number in hex. Group 1 = 0000.0C07.AC01. Group 10 = 0000.0C07.AC0A.
Which FHRP is an open standard (not Cisco proprietary)?
- HSRP
- GLBP
- VRRP
- IRDP
Answer: VRRP
VRRP (RFC 5798) is the open standard FHRP. HSRP and GLBP are Cisco proprietary. VRRP calls the forwarding router the Master (not Active).
What is the key advantage of GLBP over HSRP and VRRP?
- Faster failover
- Load balancing — all routers actively forward traffic simultaneously
- Open standard
- Simpler configuration
Answer: Load balancing — all routers actively forward traffic simultaneously
GLBP assigns different virtual MACs to different hosts, distributing traffic across all routers. HSRP and VRRP only use one active router at a time.
What command verifies HSRP state, virtual IP, and which router is Active?
- show ip route
- show standby
- show vrrp
- show ip hsrp
Answer: show standby
show standby displays HSRP group information including state (Active/Standby/Listen), virtual IP, virtual MAC, priority, and preemption status.
In HSRP, the router that is monitoring the Active router and ready to take over is called the _____ router.
Answer: Standby
The Standby router monitors the Active router via Hello messages. If the Active router fails (misses 3 Hellos), the Standby transitions to Active.
By default, is VRRP preemption enabled or disabled?
- Disabled — must be manually enabled like HSRP
- Enabled — a higher-priority router automatically becomes Master
- Depends on the IOS version
- Not supported in VRRP
Answer: Enabled — a higher-priority router automatically becomes Master
Unlike HSRP (preemption disabled by default), VRRP enables preemption by default. A recovered higher-priority router automatically reclaims the Master role.
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