Configure first hop redundancy protocols (HSRP, VRRP)

3.4 IP Services

📘CCNP Encore (350-401-ENCORE-v1.1)

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1. What are First Hop Redundancy Protocols (FHRPs)?

FHRPs are protocols that provide backup routers for hosts in a network. They ensure that if the primary router fails, another router can take over immediately, so devices can still reach the network without disruption.

Key concept:

• Devices (like servers or computers) usually have a default gateway.
• If that gateway fails, they cannot communicate outside their local network.
• FHRPs allow multiple routers to share a virtual IP. The network devices always use this virtual IP as their default gateway.
• If one router fails, another router takes over the virtual IP automatically.

Think of it as high availability for gateways.

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2. Common FHRPs

The main FHRPs you need to know for the exam are:

Protocol	Cisco Proprietary?	Default Protocol Type	Key Points
HSRP (Hot Standby Router Protocol)	Yes	Active/Standby	Only one router is active; others are standby.
VRRP (Virtual Router Redundancy Protocol)	No (standards-based)	Master/Backup	One master router handles traffic; others are backups.
GLBP (Gateway Load Balancing Protocol)	Yes	Load-sharing	Allows load balancing among multiple routers. (Less emphasized for basic FHRP exams)

For CCNP 350-401, HSRP and VRRP are primary.

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3. How HSRP Works

1. Virtual IP & MAC:
   • HSRP creates a virtual IP that hosts use as their gateway.
   • It also creates a virtual MAC address for the gateway.
2. Roles of Routers:
   • Active Router: Handles all traffic sent to the virtual IP.
   • Standby Router: Monitors the active router. If it fails, the standby becomes active.
   • Other Routers: Can be in listening state.
3. Election & Priority:
   • Routers have a priority value (0–255). Higher priority → more likely to be active.
   • Default priority is 100.
   • The active router is elected based on highest priority.
   • If priorities are equal, the router with the highest IP address becomes active.
4. Timers:
   • Hello timer: How often routers send HSRP hello messages (default: 3 seconds).
   • Hold timer: How long standby waits before declaring active router dead (default: 10 seconds).

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HSRP States

State	Description
Initial	Starting up. Not participating yet.
Learn	Knows the virtual IP but doesn’t know active router yet.
Listen	Knows virtual IP & active router. Waiting to become active/standby.
Speak	Sending hello messages; election occurs here.
Standby	Waiting to take over if active fails.
Active	Forwarding traffic to hosts.

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4. How VRRP Works

VRRP is similar to HSRP but has some differences:

1. Roles:
   • Master Router: Forwards packets sent to the virtual IP.
   • Backup Routers: Take over if master fails.
2. Election & Priority:
   • Uses a priority value (1–255). Higher priority → master.
   • Default priority: 100.
   • Ties are broken by highest IP address.
3. Timers:
   • Advertisement interval: How often master sends VRRP messages (default: 1 second).
4. Key Difference from HSRP:
   • HSRP is Cisco proprietary; VRRP is open standard.
   • VRRP defines the router forwarding traffic as Master instead of Active.

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5. Exam-Focused Commands

HSRP Example:

interface GigabitEthernet0/1
 ip address 192.168.1.2 255.255.255.0
 standby 1 ip 192.168.1.1       # Virtual IP
 standby 1 priority 110          # Optional: set priority
 standby 1 preempt               # Allow router to take over if it has higher priority

Explanation:

• standby 1 ip 192.168.1.1 → sets the virtual IP.
• priority 110 → sets this router to be more likely active.
• preempt → allows router to take over if it becomes higher priority after a reboot.

VRRP Example:

interface GigabitEthernet0/1
 ip address 192.168.1.3 255.255.255.0
 vrrp 1 ip 192.168.1.1
 vrrp 1 priority 120
 vrrp 1 preempt

Explanation:

• Similar to HSRP but uses vrrp instead of standby.

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6. Key Exam Tips

1. Roles and terminology matter:
   • HSRP → Active/Standby.
   • VRRP → Master/Backup.
2. Default priorities and timers:
   • Know that HSRP default priority is 100, hello 3s, hold 10s.
   • VRRP default priority 100, advertisement 1s.
3. Preemption:
   • Without preempt, a router with higher priority cannot take over until active fails.
4. Virtual IP is always the gateway for hosts:
   • Physical router IPs are secondary; hosts only use virtual IP.
5. Multiple routers can share one virtual IP:
   • Ensures high availability in IT networks (for example, web servers or DNS servers).

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7. Summary Table – HSRP vs VRRP

Feature	HSRP	VRRP
Proprietary	Cisco	Standard (RFC 5798)
Roles	Active / Standby	Master / Backup
Default Priority	100	100
Virtual MAC	Yes	Yes
Preemption	Optional	Optional
Use	Gateway redundancy for Cisco networks	Gateway redundancy for mixed vendors

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✅ Key Takeaways for the Exam:

• Understand what HSRP and VRRP do – provide redundancy for default gateways.
• Know roles, states, and election process.
• Know basic commands and configuration options (IP, priority, preempt).
• Recognize differences between HSRP (Cisco only) and VRRP (standard).
• Focus on virtual IP and MAC addresses, as these are what hosts rely on.

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