HSRP Active/Active Scenario

[KATTUBAVA E.S]

Hi Experts,

I am having a question reqarding HSRP functionality in the below scenario.,

                             R1---Fa0/0----------------------Fa0/1---R2

                               |                                               |

                               |                                               |

                               |__________Switch___________|

                                                     |

                                                     |                                    

                                                     |

                                                 Host A

Lets say R1 is configured with highest priority to become Active router and Host A is using HSRP ip address as deafult Gateway.So HOST A will forward the packets which are destined outside its network. Now if the L2 connectivity between the router got disturbed (ie Interface Fa0/0 of R1 is shutdown), then HSRP signalling will be down between thses routers and R1 still acts as ACTIVE router however R2 will also assume itself as ACTIVE router as HSRP signalling is broken. Now in this case of Active/Active Scenario, We do have a single MAC address for HSRP and which can't be assigned for multiple devices, how does the forwarding happens from the HOST A?

(Note: Assume Preemption is enabled on both routers)

Thanks

-Bava

[ajay chauhan]

once connectivity between R1 and Switch is down think like that part is isolated from network . While standby router will take over and act as primary one so forwarding will happen through R2. Same mac will be act for HSRP and get associated with standby router.

Thanks

Ajay

[KATTUBAVA E.S]

Hi Ajay,

Let me make it clear now, R1 and R2 are directly connected via FastEthernet connection and if pull the cable and makes no room for HSRP signalling, then what will happen??

R1,R2 and HostA are connected to the same switch..

-Bava

[JohnTylerPearce]

I believe that the HSRP signaling is done for that specific vlan. So if you were to pull the direct cable going from R1 to R2,

I wouldn't think that would have any affect as far as HSRP goes (unless you have HSRP tracking set up). The HSRP

signaling should be done via the LAN segment between R1 and R2 via the LAN segment. Please correct me if I'm wrong.

[Latchum Naidu]

Hi Bava,

What are you trying to achieve?
In real you dont need L2 connection between those two routers.
The hsrp hot beat happening from switch as they both routers connected to switch.
In the above scenario if the l2 connection between switch and R2 is gone then the packet will go through R2.

If the above not answered you, please tell us clearly what you are trying to achieve or understand.

Please rate the helpfull posts.
Regards,
Naidu.

[JohnTylerPearce · Accepted solution]

R1---------------------------------R2

|                                     |

|-------------[SwitchA]----------|

                     |

                     |

                  Host A

This is the scenario in this you have stated above.

Lets say we have a network of 192.168.1.0/24 in the LAN segemnt R1-SwitchA-R2 and the network of 10.0.0.1/30 between

R1 and R2. The configurations of HSRP will be done on the FastEthernet interfaces facing the LAN segment R1-SwitchA-R2.

Now in this example R1 will be the Active and R2 will be Standby. If R1 goes down so to speak or the interface facing the

LAN segment network R1-SwitchA-R2, then R2 will take over as the standby, using the same Virtual IP address. If the interface

facing R2 from R1 goes down, nothing will happen by default. You don't really need this connection unless you have a specific reason for it. Now with HSRP tracking, which people use to track connects to the ISP, because if R1 has a connectin to your ISP and it went down, that not going to cause a HSRP election. but at the same time if HSRP is still pointint to that router as the default gateway, internet connections will not work. This is why you would implement HSRP Tracking.

R1

----

int fa0/0

ip address 192.168.1.2 255.255.255.0

standby 1 ip 192.168.1.1 255.255.255.0

standby 1 priority 101

standby 1 preempt

R2

----

int fa0/0

ip address 192.168.1.3 255.255.255.0

standby 1 ip 192.168.1.1 255.255.255.0

standby 1 preempt

(The default priority will be 100)

In this simple configuration, when the fa0/0 interface goes down on R1, it will decrement the priority by 10 (which is the default setting, this can be adjusted). This will make R2 which has a priority of 100 (by default) the active router in the HSRP group 1. When the fa0/0 interface on R1 comes back up, R1 will become the Active router because it will have a higher priority of 101.

R1 - Priority = 101 | (If interface goes down) Priority = 101 - 10 = 91

R2 will then become the Active router because R2 Priority = 100 R1 Priority = 91

When the interface on R1 comes back up

R1 - Priority = 101 (This is higher than R2's priority of 100)

R2 will then become Standby because R2 Priority of 100 < 101.

This is just a simple configuration, you can also do authentication, change timers, etc etc.

[KATTUBAVA E.S]

Thanks all for the valuable response..