FHRP - jibingl/CCNA-CCNP GitHub Wiki

First Hop Redundancy Protocols

Enable two or more routers to protect/backup default-gateway for a subnetwork.

Abbreviation Full-name Property Router Mode MulticastIP vMAC Load Balancing
HSRP Hot Standby Reouter Protocol Cisco active/standby 224.0.0.2/102 0000.0c07.acXX 0000.0c9f.fXXX Among subnets
VRRP Virtual Router Redundancy protocol Open-standard master/backup 224.0.0.18 0000.5e00.01XX Among subnets
GLBP Gateway Load Balancing Protocol Cisco AVG/AVF 224.0.0.102 0007.b400.XXYY Within ONE subnet

Notes:
HSRP has two versions, so there are two values sometimes.
vMAC is used for updating switches' MAC address-table.
The 'X' of vMAC is the group number of associated protocol, and the 'Y' is the AVF number.

HSRP

Typicial Topology

           R2             SW2          SW4
ISP1------(+)-g0/0_.252--------[=]----------[=]-------.4--PC4
         standby               | \        /  `-------.3--PC3
                               |   \    /
               vIP_.254        |     \/     172.16.0.0/24    default-getaway_.254
                               |     /\
                               |   /    \
         active                | /        \  .--------.2--PC2
ISP2------(+)-g0/0_.253--------[=]----------[=]--------.1--PC1
           R1             SW1          SW3

After configuration, HSRP will generates a virtual MAC, and then broadcast this vMAC out to keep SWs' ARP table updated when failure occurred. The routers membered of HSRP use reserved multicast IP address to keep communicating by sending send Hello msg.

Configuration Example

R1(config)#interface g0/0
R1(config-if)#standby version 2                    //Optional
R1(config-if)#standby 1 ip 172.16.0.254            //'1' is HSRP group number. The range is 0-255 in HSRP version1 , v2 is 0-4095. 
R1(config-if)#standby 1 priority 200               //Default is 100 <0-255>. (Highest priority will be active router; if tied, highest IP)
R1(config-if)#standby 1 preempt                    //Take over back the active role anyway

R2(config-if)#standby version 2                    //Routers MUST match the same version
R2(config-if)#standby 1 ip 172.16.0.254

Configurations of VRRP and GLBP are the same as HSRP, replace standby with vrrp or glbp.

HSRP Load Balancing

Load balancing among different subnets/VLANs. Assign different router as the active router for each subnet/VLAN.

VRRP

Load balancing among different subnets/VLANs. Assign different router as the master router for each subnet/VLAN.

GLBP Load Balancing

Load balancing across multiple routers within ONE subnet/VLAN.

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