HSRP IP Route Tracking
In this article we will discuss about HSRP and do a lab on it.
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Quick reminder about HSRP
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+ Hot Standby Router Protocol (HSRP) is a Cisco proprietary protocol.
+ With HSRP, two or more devices support a virtual router with a fictitious MAC address and unique IP address
+ Hosts use this IP address as their default gateway and the MAC address for the Layer 2 header
+ The virtual router’s MAC address is 0000.0c07.ACxx , in which xx is the HSRP group. Multiple groups (virtual routers) are allowed.
+ The Active router forwards traffic. The Standby router is backup and monitors periodic hellos (multicast to 224.0.0.2,
UDP port 1985) to detect a failure of the active router.
+ The active router is chosen because it has the highest HSRP priority (default priority is 100). In case of a tie, the router
with the highest configured IP address wins the election
+ A new router with a higher priority does not cause an election unless it is configured to preempt.
HSRP States
+ Initial: HSRP is not running.
+ Learn: The router does not know the virtual IP address and is waiting to hear from the active router.
+ Listen: The router knows the IP and MAC of the virtual router, but it is not the active or standby router.
+ Speak: Router sends periodic HSRP hellos and participates in the election of the active router.
+ Standby: Router monitors hellos from active router and assumes responsibility if active router fails.
+ Active:Router forwards packets on behalf of the virtual router.
Load balancing traffic across two uplinks to two HSRP routers with a single HSRP group is not possible. The trick is to use two
HSRP groups:
+ One group assigns an active router to one switch.
+ The other group assigns another active router to the other switch.
(Reference: SWITCH official Certification Guide)
That is all for the boring HSRP theory, let do a lab to understand more about HSRP! We will use the topology below for this lab:
Tasks in this lab:
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+ Configure IP addresses as shown and run EIGRP on R2, R3, R4
+ Configure HSRP: R2 is the Active HSRP while R3 is the Standby HSRP
+ Tracking route to 4.4.4.4, traffic should goes to R3 once the route to 4.4.4.4 is lost in R2 or the metric to R4’s loopback interface increases.
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IP Address and EIGRP Configuration
R1 (configured as a host)
no ip routing
ip default-gateway 123.123.123.254 //This is the virtual IP of HSRP group
interface FastEthernet0/0
ip address 123.123.123.1 255.255.255.0
no shutdownR2
interface FastEthernet0/0
ip address 123.123.123.2 255.255.255.0
no shutdown
!
interface FastEthernet1/0
ip address 24.24.24.2 255.255.255.0
no shutdown
!
router eigrp 1
network 24.0.0.0
network 123.0.0.0
R3
interface FastEthernet0/0
ip address 123.123.123.3 255.255.255.0
no shutdown
!
interface FastEthernet1/0
ip address 34.34.34.3 255.255.255.0
no shutdown
!
router eigrp 1
network 34.0.0.0
network 123.0.0.0R4
interface Loopback0
ip address 4.4.4.4 255.255.255.0
!
interface FastEthernet0/0
ip address 24.24.24.4 255.255.255.0
no shutdown
!
interface FastEthernet1/0
ip address 34.34.34.4 255.255.255.0
no shutdown
!
router eigrp 1
network 4.0.0.0
network 24.0.0.0
network 34.0.0.0
HSRP Configuration
R2
interface FastEthernet0/0
standby 10 ip 123.123.123.254
standby 10 priority 200
standby 10 preemptR3
interface FastEthernet0/0
standby 10 ip 123.123.123.254
standby 10 priority 150
standby 10 preempt
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Note: The virtual IP address of HSRP group must be in the same subnet of the IP address on this interface (Fa0/0)
After entering above commands we will see R2 takes Active state after going from Speak to Standby:
%HSRP-5-STATECHANGE: FastEthernet0/0 Grp 10 state Speak -> Standby
*Mar 1 00:10:22.487: %HSRP-5-STATECHANGE: FastEthernet0/0 Grp 10 state Standby -> Active
*Mar 1 00:10:22.871: %SYS-5-CONFIG_I: Configured from console by console
The “show standby” command on R2 confirms its state: