VRRP (Virtual Router Redundancy Protocol)

If I had access to a switch lab, I wouldn’t ask this question. Suppose you configure VRRP such that a backup VRRP client learns timers from the master (which has non-default timers set). A failure then occurs so that the backup becomes the new master. Would the new master continue to use the timers it learned from the prior master, or would it revert to use VRRP defaults?

Hi Andrew,

Just tested this, when the backup VRRP becomes the master, it uses its own timer values. Not the ones from the failed master.

Rene

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Hello NetworkLessons team,

Maybe there is a little typo in the text below:
“VRRP uses different terminology than HSRP. SW1 has the best priority and will become the master router. SW2 will become a backup router (instead standby).”

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Hello Boris

Yes, this is a typo thank you, I’ll let @ReneMolenaar know…

Thanks again!

Laz

Hi,

Ho can I prevent an effect like this picture?

Thanks

Hello Giovanni

The trombone effect is something that we see with first hop redundancy protocols such as HSRP and VRRP when you distribute layer 2 across multiple datacenters in remote locations. As in the example you shared, this effect results in suboptimal switching of traffic. The solution to this is the use of FHRP isolation which is applied in Cisco’s Overlay Transport Virtualisation (OTV) infrastructure.

FHRP isolation allows for the containment of the election process within each site so that a local device is always elected as the active device.

The following Cisco community post summarizes FHRP isolation and how it works to resolve this problem:


I hope this has been helpful!

Laz

Does the Preemption in VRRP enabled by default compare to HSRP? I saw the Preemption shows enabled once VRRP command is implemented.

Another question is that does the preemption in VRRP work the same way as in HSRP? The switch with the highest priority will become the master device immediately.

Hello Po

In HSRP, preemption is disabled by default. However, in VRRP, preemption is enabled by default. Preemption works the same way in VRRP as it does in HSRP. The device with the highest priority will immediately take the role of the Active or Master device.

I hope this has been helpful!

Laz

Thank you Laz. I got it now

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Hi Laz,

Could you explore here how is load-balancing being performed here mean how traffic will be passed through and when will be though SW1 and when through SW2?

Hello Pradyumna

VRRP does not automatically load balance traffic across all participating routers. Load balancing is achieved by configuring half of the hosts in a subnet to use one default gateway, and the other half to use the other default gateway.

VRRP allows you to create multiple virtual IP addresses. Within each participating router, you can assign different priorities to each virtual IP. So in a scenario where you have R1 and R2, and 192.168.1.3 and 192.168.1.4 as virtual IP addresses, you can configure the following:

  • R1 configured with 192.168.1.3 with a higher priority
  • R2 configured with 192.168.1.4 with a higher priority

Then, in your subnet, you can assign 192.168.1.3 as the default gateway of half of your hosts, and 192.168.1.4 for the other half. If one of the routers fails, it adopts both virtual IP addresses so all hosts can still function.

So to summarise, with VRRP you don’t load balance traffic, but you load balance hosts. In order to perform real automatic load balancing it is preferable to employ Gateway Load Balancing Protocol (GLBP). You can learn more about this at the following lesson:

I hope this has been helpful!

Laz

Thanks laz almost understand but still having doubt that suppose if one of virtual gateway fails then whole traffic will pass through active router then which host traffic will be prioritize if they are sending traffic simultaneously

FYI Suppose we have no of host.

Hello Pradyumna

Let’s say you have two gateways, R1 and R2, and let’s say their virtual IP addresses are 192.168.1.3 and 192.168.1.4. Let’s say you’ve configured them in the following way:

  • R1 configured with 192.168.1.3 with a higher priority and 192.168.1.4 with a lower priority
  • R2 configured with 192.168.1.4 with a higher priority and 192.168.1.3 with a lower priority

Let’s also say that you have 100 hosts in this subnet, and 50 of them use 192.168.1.3 as the default gateway and the other fifty use 192.168.1.4.

Under normal circumstances, half of the hosts send their default gateway traffic to R1, and the other half to R2.

Now let’s say R2 fails. What happens? R1 obtains both virtual addresses. This means that traffic from all 100 hosts will go to R1.

Note here that the priority set up in the routers does not have to do with the prioritization of traffic, but simply with which virtual IP address will be adopted by each device. If R2 fails, R1 obtains both virtual IP addresses, and simply functions as the single gateway for all hosts. Traffic is served on a first come first serve basis.

I hope this has been helpful!

Laz

I can you tell me how 2 switches can exchange information about priority to themselves ?
I saw that there is not any information about backup switches.

And also what happen if every switches set himself as master switch?

And also…what happen if the vrrd ID is the same on any vlan configuration even with different subnets ?

Thanks as always

Hello Giovanni

Take a look at the diagram from the lesson:


When configured correctly with VRRP, SW1 and SW2 will communicate with each other over the link with SW3. If you configure ports Fa0/17 and Fa0/19 of SW1 and SW2 respectively, you would have something like this:

SW1(config)#interface fa0/17
SW1(config-if)#vrrp 1 ip 192.168.1.3
SW1(config-if)#vrrp 1 priority 150

SW2(config-if)#interface fa0/19
SW2(config-if)#vrrp 1 ip 192.168.1.3

It is the vrrp 1 prioritycommand that specifies the priority of the particular virtual IP. The number 1 indicates the VRRP group. In this case, SW1 has priority for that virtual IP so it becomes the master gateway.

So it is the priority that makes a gateway become the master or the backup.

If the switches communicate correctly over VRRP, this will never happen. One of the two will become master, and the other will be backup. This is determined by the priority. If the priority is the same, then the router that owns the IP address (the address is configured on its physical interface) will become master.

Not sure what you mean by VRRP ID… can you clarify?

I hope this has been helpful!

Laz

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I mean the VRRP group, can I configure the same vrrp group with different vlans and different subnets?

Hello Giovanni

I see what you mean… The VRRP group number must be the same on the interfaces that you choose to participate in VRRP. By using the same ID number, you are pairing up those specific interfaces together.

Secondly, the IP addresses of the physical interfaces, as well as the virtual IP address must be in the same subnet. Even if you could configure an IP address in a different subnet, your hosts will be unable to reach that gateway (whether a physical or virtual IP address) in the event of a failure of one of the switches.

I hope this has been helpful!

Laz

I saw that the switch can only configure 255 VRRP groups.

What can I do to configure VRRP in each SVI interface, if I have more than 255 vlans?

INTEGER<1-255> Virtual router identifier

Thanks

Hello Giovanni

Note that the VRRP group number must be unique within the VLAN. So you can use the same VRRP group number in different VLANs so you have no limitation as to the number of VLANs for which you configure VRRP. The purpose of the group number is to be able to assign multiple virtual IP addresses with varying priorities for the purpose of load balancing, as specified in the lesson.

I hope this has been helpful!

Laz

Hello in the case in which you have more links under the routers in which VRRP is configured as would be the configuration