There are occasions when 2 Routers are linked to supply excessive availability to community and HSRP is configured on the LAN aspect of Routers with one performing as main and different its HSRP backup. Such a setup could be good in some circumstances like ptp hyperlinks on serial interfaces.
Nevertheless when we’ve got Ethernet medium and direct hyperlink failure occurs, HSRP cant reply to this state of affairs and nonetheless retains of forwarding site visitors unaware of the hyperlink failure.
Instance State of affairs: IP SLA with HSRP
Under is an instance state of affairs exhibiting how HSRP will be configured to fulfill the oblique hyperlink failures by use of IP SLA configuration with HSRP.
Routers R1 and R2 have HSRP configured on LAN aspect (HSRP IP = 192.168.12.3).
Each the routers have static routes pointing in direction of R3 on the distant aspect.
In between we will see Change SW2 which acts as layer 2 and connects segments of R1-R3 and R2-R3.
Configuration:
R1#
Interface FastEthernet0/0
ip tackle 192.168.12.1 255.255.255.0
standby 1 ip 192.168.12.3
standby 1 preempt
!
interface FastEthernet0/1
ip tackle 192.168.13.1 255.255.255.0
!
ip route 0.0.0.0 0.0.0.0 192.168.13.3R2#
interface FastEthernet0/0
ip tackle 192.168.12.2 255.255.255.0
standby preempt
standby 1 ip 192.168.12.3
standby 1 precedence 90
standby 1 preempt
!
interface FastEthernet0/1
ip tackle 192.168.23.2 255.255.255.0
!
ip route 0.0.0.0 0.0.0.0 192.168.23.3
Now that HSRP configuration is in place, community administrator realizes that any oblique failure on the hyperlink between R3 and R1 is not going to be seen by R1 and nonetheless R1 stays the HSRP grasp and carry on forwarding the site visitors.
The answer will be reached if R1 displays a distant IP – say Loopback 3.3.3.3 of R3 and decrements HSRP precedence to a worth decrease than that of R2.
Now lets see how we will configure R1 to fulfill this requirement –
R1#
ip sla monitor 1
sort echo protocol ipIcmpEcho 3.3.3.3
frequency 5
ip sla monitor schedule 1 life ceaselessly start-time now
!
observe 1 rtr 1 reachability
!
interface FastEthernet0/0
standby 1 observe 1 decrement 20
Now that we’ve got configured IP SLA on R1, lets see the traditional output of HSRP (standby 1) command
R1#present standby temporary
P signifies configured to preempt.
|
Interface Grp Prio P State Lively Standby Digital IP
Fa0/0 1 100 P Lively native unknown 192.168.12.3R2#sh standby temporary
P signifies configured to preempt.
|
Interface Grp Prio P State Lively Standby Digital IP
Fa0/0 1 90 P Standby 192.168.12.1 native 192.168.12.3
R1 is grasp whereas R2 is standby in regular state of affairs. Lets shut interface Fa0/0 of R3 which connects to R1 by way of Change.
Lets remember that R1 HSRP grasp has default precedence of 100 and can decrement by 20 = turns into 80 if reachability to R3 loopback (3.3.3.3) is misplaced.
R3(config-if)#int fa0/0
R3(config-if)#shut
R1#present standby brie
P signifies configured to preempt.
|
Interface Grp Prio P State Lively Standby Digital IP
Fa0/0 1 80 P Standby 192.168.12.2 native 192.168.12.3
R1#present standby brie
P signifies configured to preempt.
|
Interface Grp Prio P State Lively Standby Digital IP
Fa0/0 1 80 P Standby 192.168.12.2 native 192.168.12.3R2#present standby temporary
P signifies configured to preempt.
|
Interface Grp Prio P State Lively Standby Digital IP
Fa0/0 1 90 P Lively native 192.168.12.1 192.168.12.3
As seen above, mixture of HSRP and IP SLA will make resolution when we’ve got a number of Routers operating HSRP and the place we have to detect any oblique hyperlink failure or Layer 1 hyperlink failure to reroute the site visitors by way of backup HSRP Router.
