FHRP (First Hop Redundancy Protocol) is a group of protocols that provide high availability for the default gateway in a local network. The primary goal of FHRP is to automatically switch between multiple routers or Layer 3 switches in case the primary device fails.
Main FHRP protocols:
- HSRP (Hot Standby Router Protocol) — Cisco proprietary.
- VRRP (Virtual Router Redundancy Protocol) — open standard.
- GLBP (Gateway Load Balancing Protocol) — Cisco proprietary with load balancing.
Purpose: Ensure continuous network access and minimize downtime during device failures.
# FHRP - First Hop Redurancy Protocol
#FHRP | Terminology | Multicast IP | Virtual MAC | Cisco?
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# HSRP | Active/Standbay | v1:224.0.0.2 | 0000.0c07.acXX | Yes
# | | v2:224.0.0.102| 0000.0c9f.fXXX |
# VRRP | Master/Backup | 224.0.0.18 | 0000.5e00.01XX | No
# | | | |
# GLBP | AVG/AVF | 224.0.0.102 |0007.b400.XXYY | Yes
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# R1 (Active)<==Hello messages==>R2 (Standbay)
# .254 .253
# \ /
# \ /
# \ /
# \ /
# \ /
# VIP <-has own virtual MAC
# .252
#
# / \
# / \
# / \
# set as a default GW | set as a default GW
#
#Gratuitous ARP: ARP replies sent without being requested (no ARP request messages was recieved)
#Then the Active router failed, the Standbay router will not recieved Hello packet and send a Gratuitous ARP
#packet and it will update all FDB tables on all switches in their domain.
#
#By default, if router back online it doesn`t become an Active router.
#You have to configure "preemption", so the old Active router does not take back its old role.
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#HSRP (Cisco) Hot Standbay Router Protocol
#v1 -
#v2 - support IP v6 and increase the number of groups tha can be configured
#Active and Standbay routers are elected
#Multicats address for v1 = 224.0.0.2
#Multicats address for v2 = 224.0.0.102
#Virtual MAC for v1 = 0000.0c07.acXX, where XX is a group number
#Virtual MAC for v2 = 0000.0c9f.fXXX, where XXX is a group number
#
#In a situation with multiple subnets/VLANs, you can configure a different Active router in each
#subnets/VLANs to load balance.
#VRRP - Virtual Router Redurancy Protocol
#Open standart
#Master and Backup routers are elected
#Multicats address = 224.0.0.18
#Virtual MAC = 0000.5e00.01XX, where XX is VRRP group number
#Example: For the group with number 200=0xc8, MAC address will be 0000.5e00.01c8
#GLBP - Gateway Load Balancing Protocol (Cisco)
#Load balancing among multiple routers within a single subnet
#An AVG (Active Virtual Gateway) is elected
#Up to 4 AVFs (Active Virtual Forwarders) are assingned by the AVG (the AVG itself can be an AVF too)
#Each AVF acts as a default gateway for a portion ot the hosts in the subnet.
#Multicats address = 224.0.0.102
#Virtual MAC = 0007.b400.XXYY, where XX is a GLBP group number, YY - AVF number
#CONFIGURING HSRP
#R1,R2,SW1,SW2
#R1
#int g0/0 - connected to a SW1,IP addr = 172.16.0.253/24
#int g1/0 - connected to a cloud, IP addr = 203.0.113.1
#
#R2
#int g0/0 - connected to a SW2,IP addr = 172.16.0.252/24
#int g1/0 - connected to a cloud, IP addr = 203.0.113.5
#VIP = 172.16.0.254/24
#SW1 connected to SW2
#R1
int g0/0
standbay version 2
standbay 1 ip 172.16.0.254
standbay 1 priority <0-255>
#Active router is determinated in this order:
#Highest priority (by default 100)
#Highest IP address
standbay 1 priority 200
standbay 1 preempt #need to use if you want R1 always become Active, after back online
#R2
int g0/0
standbay version 2
standbay 1 ip 172.16.0.254
standbay 1 priority 50
standbay 1 preempt
#Version must be the same on the routers
show standbay