day 29 - First Hop Redundancy protocols

Describe the purpose of the first hop redundancy protocol

designed to protect the default gateway by allowing 2 or more routers to provide backup for that address

3 types of FHRP

• HSRP

• VRRP

• GLBP

VIP

virtual IP address

How do routers negotiate their roles?

They send multicast

• one will become active and one will become standby in FHRP

two roles in FHRP

Active and Standby

each FHRP uses a different

virtual Mac address for the default gateway

what needs to be updated in FHRP if the active router fails

• the switch needs to be updated, by the backup router sending gratuitous ARP replies

gratuitous arp

ARP replies sent without being requested

FHRPs are

‘non preemptive’

non preemptive means

it won’t give up its role as the active router

The active router replies to arp requests

using the virtual mac address (the backup will send out gratuitous ARPs if the active fails)

HSRP

hot standby router protocol

Hot Standby Router Protocol

• Active/Standby are elected

• version 2 is for IPv6

• you can configure a different active router in each subnet/VLAN to load-balance (like in STP with multiple roots)

VRRP

virtual router redundancy protocol

Virtual router redundancy protocol

• open standard

• A Master and Backup Router (not active/standby)

  • Can configure a different master router in each subnet/vlan to load-balance

GLBP

gateway load-balancing protocol

GLBP

• load balances among multiple routers WITHIN a single subnet (it’s the best one)

  • an AVG (active virtual gateway) is elected then up to 4 AVF’s (they act as default gateway)

AVF

Active virtual forwarders in GLBP that act as default gateway

why do we use GLBP and FHRP

to protect the default gateway and to have active/backup routers in case one goes down

configure HSRP

• int g0/0

• standby # ip 172.16.0.254(default gateway)

• standby # priority ? (to determine active router)

• standby # preempt (causes router to take active role even if another one is)

put HSRP in version 2

standby version 2

HSRP command to make the router the active router

Standby # preempt

HSRP command to make router higher priority to be active

Standby # priority #