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FHRP stands for First Hop Redundancy Protocol, a group of protocols designed to ensure high availability of the default gateway in a network. In a typical setup, hosts on a LAN are configured with a single default gateway. If that gateway fails, all traffic leaving the subnet fails too. FHRPs solve this by providing automatic failover between multiple routers.
Common FHRP Protocols:
- HSRP (Hot Standby Router Protocol): Cisco proprietary; allows one active router and one or more standby routers.
- VRRP (Virtual Router Redundancy Protocol): Open standard; similar to HSRP but allows the master router to be any router.
- GLBP (Gateway Load Balancing Protocol): Cisco proprietary; provides redundancy and load balancing across multiple gateways.
How FHRP Works:
- Virtual IP Address is shared among multiple routers.
- One router is elected as active (or master).
- Other routers are in standby or backup state.
- If the active router fails, another router automatically takes over the virtual IP and continues forwarding traffic.
Why Use FHRP?
- Minimizes downtime
- Ensures uninterrupted network access
- Provides seamless failover
- Supports load balancing (GLBP only)
You Should Know:
1. Configuring HSRP on Cisco Routers
To set up HSRP on a Cisco router, use the following commands:
interface GigabitEthernet0/0 ip address 192.168.1.1 255.255.255.0 standby version 2 standby 1 ip 192.168.1.254 standby 1 priority 110 standby 1 preempt standby 1 track GigabitEthernet0/1 20
– `standby 1 ip 192.168.1.254` sets the virtual IP.
– `standby 1 priority 110` assigns a priority (higher = preferred active).
– `standby 1 preempt` allows the router to reclaim active status if it comes back online.
– `standby 1 track` monitors another interface and adjusts priority if it fails.
2. VRRP Configuration on Linux (Keepalived)
For Linux-based redundancy, use `keepalived` for VRRP:
sudo apt install keepalived -y
Edit `/etc/keepalived/keepalived.conf`:
vrrp_instance VI_1 {
state MASTER
interface eth0
virtual_router_id 51
priority 100
advert_int 1
authentication {
auth_type PASS
auth_pass secret
}
virtual_ipaddress {
192.168.1.254/24
}
}
Restart the service:
sudo systemctl restart keepalived
3. Verifying FHRP Status
- Cisco HSRP Verification:
show standby brief
- VRRP Verification (Linux):
ip addr show eth0 journalctl -u keepalived -f
4. Simulating Failover for Testing
- Shut down the active router’s interface:
interface GigabitEthernet0/0 shutdown
- Check standby takeover:
show standby
5. GLBP Load Balancing
Configure GLBP for redundancy + load balancing:
interface GigabitEthernet0/0 glbp 1 ip 192.168.1.254 glbp 1 priority 150 glbp 1 preempt glbp 1 load-balancing round-robin
What Undercode Say
FHRP is essential for maintaining network resilience. Whether using HSRP, VRRP, or GLBP, these protocols ensure minimal downtime. For Linux admins, Keepalived offers a robust VRRP implementation, while Cisco environments rely on HSRP/GLBP. Always test failover scenarios and monitor logs (show standby, journalctl). Load balancing with GLBP optimizes traffic distribution, making it ideal for high-availability setups.
Expected Output:
- A functional FHRP setup with automatic failover.
- Verified logs confirming active/standby transitions.
- Successful load balancing (if using GLBP).
- Reduced downtime during gateway failures.
References:
Reported By: Ahmed Bawkar – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
