~/netref / First-Hop Redundancy
##

First-Hop Redundancy (FHRP)

Give hosts a single virtual default gateway backed by two or more routers, so a failure is invisible.

ProtocolVendorRolesMulticast
HSRPCiscoActive / Standbyv2 224.0.0.102
VRRPOpen (RFC 5798)Master / Backup224.0.0.18
GLBPCiscoAVG + load balance224.0.0.102

// how it works

  • Hosts use one virtual IP/MAC as their gateway
  • If the active router fails, standby takes over
  • GLBP also load-balances across routers
  • Tracking can lower priority when an uplink drops
hsrp / vrrp / glbp · cisco ios 
! HSRP (active/standby)
interface Gi0/0
 ip address 10.0.1.2 255.255.255.0
 standby version 2
 standby 1 ip 10.0.1.1
 standby 1 priority 110
 standby 1 preempt
 standby 1 track Gi0/1 20
!
! --- VRRP alternative ---
 vrrp 1 ip 10.0.1.1
 vrrp 1 priority 110
 vrrp 1 preempt
!
! --- GLBP alternative ---
 glbp 1 ip 10.0.1.1
 glbp 1 load-balancing round-robin
verify 
show standby brief
show vrrp brief
show glbp brief
show track brief