Routing Protocols gives redundancy at layer 3
Redundancy between 2 switches, you connect 2 or more links between them.
Similarly to allow redundancy for your clients, you might want to connect 2 routers as the gateway to exit from the network.
FHRP First Hop Redundancy Protocol
Gives redundancy at First Hop level gives redundancy at the gateway level
On PC I can configure only one IP address as default gateway. If that device (router) goes down then I would need to configure manually on my PCs the new default gateway.
So from the perspective of PC needs --> First Hop Redundancy
FHRP technology allows the 2 routers to share a single IP address. Or we can say a shared ip address between the 2 routers which is called as the VIP – Virtual IP .where you have the rights to prefer a specific router as forwarding router and another routers as Backup router.
Along with VIP the routers will also share mac address.
Forwarding router is the router which will be answering for the VIP and will forward the traffic .
FHRP establish the relationship between the 2 routers, hellos are exchanges between those routers and incase the forwarding/active/master router goes down then the standby router will become active and will now be answering for the VIP and will forward traffic for the clients.
We have the rights which router to be preferred as forwarding/active/master and backup/standby by manipulating the priority values.
Remember FHRP is the technology it is not the actual implementation.
There are 3 main FHRP Implementations HSRP VRRP AND GLBP
Protocol Features |
HSRP - |
VRRP - |
GLBP - |
Scope |
Cisco Proprietary |
IEEE standard |
Cisco proprietary |
Standard |
RFC2281 |
RFC3768 |
none |
OSI Layer |
Layer-3 |
Layer-3 |
Layer-2 |
Load Balancing |
No |
No |
Yes |
Multicast Group IP address |
224.0.0.2 in version 1 |
224.0.0.18 |
224.0.0.102 |
Transport Port Number |
UDP 1985 |
UDP 112 |
UDP 3222 |
Timers |
Hello – 3 sec |
Advertisement – 1 sec |
Hello – 3sec |
Hold – 10 sec |
Master down time = 3*Advertisement Time |
Hold – 10sec |
|
Election |
Active Router:1.Highest Priority2. Highest IP address (Tiebreaker) |
Master Router: (*) |
Active Virtual Gateway: |
1-Highest Priority |
1-Highest Priority |
||
2-Highest IP (Tiebreaker) |
2-Highest IP (Tiebreaker) |
||
Router Role |
One Active Router, One Standby Router , One or more listening Router/s |
– One Active Router- One or |
One AVG (Active Virtual Gateway)- up to 4 AVF |
Preempt |
If Active Router(Highest Priority) is down and up again, Preempt should be configured to become a Active Router again |
By default Preempt is ON in VRRP, |
If Active Router(Highest Priority) is down |
Group Virtual Mac Address |
0000.0c07.acxx |
0000.5e00.01xx |
0007.b4xx.xxxx |
IPv6 support |
Yes |
No |
Yes |
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