What is Uplinkfast in STP? | Definition and How It Works?

If you’re into networking, you’ve probably heard of the “Spanning Tree Protocol.” It helps make a loop-free setup in a switched Ethernet network.

To make it work even better, there are features like UplinkFast. In this article, we’ll see what UplinkFast is and how it works in the Spanning Tree Protocol. Let’s dive in!

The STP protocol was developed to prevent loops in the OSI model layer 2. In a cable failure that occurs in a redundant network, several features have been created due to the high STP Convergence time.

Spanning Tree Uplinkfast Definition

What Exactly is STP Uplinkfast in Networking, and What Does it Do?

In today’s networks, having backup routes is a must. The server part of a business network should always be running. This ensures that servers can serve customers without any breaks. Also, the UplinkFast thing is only for Cisco.

So, in these networks, having a backup is really important. Even though it creates a loop in the 2nd layer devices during the backup, the STP protocol was made to handle it. For instance, if there are multiple cables connected to a switch and one fails, the other needs to take over. That’s where STP comes in handy.

When one cable connected to the switch breaks, it might take a bit for the other one to start working. This inactive cable can take up to 50 seconds to get going. To speed things up, you can set up UplinkFast on the switch.

If you remember, we have stated that in order to increase STP performance. Thus, we need to configure the interfaces of devices such as PCs and servers connected to the Switch as PortFast.

How Does Uplinkfast Work, and How Does It Improve Spanning Tree Protocol Performance?

When a cable breaks, the STP protocol kicks in. It quickly updates the network map for a speedy recovery. This happens on a switch with Blocking Mode in a backup network.

Additionally, the Switch uses the Listening and Learning port states. That is, it will switch from processing to Forwarding mode.

Also, this Cisco feature only works in the access layer of the network. Using this guarantees that the network stays connected. So, if a switch goes down, the uplink fast steps in right away. It quickly turns on the other backup link to keep the communication going.

If you are going to use this, the Switch must have a Blocking port. This way, you can quickly activate the alternative path.

When you examine the image below, you can see that Switch1 has a backup path.

Reviewing Port Status of Cisco Switch

As a result, Switch1’s network cable failed. In this case, this feature will put the GigabitEthernet0/2 interface into Forwarding mode in 15 to 20 seconds.

What are the Possible Disadvantages of Using UplinkFast in a Network?

UplinkFast improves the Spanning Tree Protocol (STP) performance. It reduces downtime during network failures. However, be aware of its drawbacks. These limitations can impact your network.

Therefore, understanding both sides is crucial. Use UplinkFast wisely to maximize its benefits. Stay informed to maintain a stable network environment.

UplinkFast is for access layer switches only. It does not work for distribution or core layers. This limitation impacts your network’s redundancy.

If you use devices beyond the access layer, consider other methods. Also, complex network setups may not benefit from UplinkFast.

Consequently, you might face gaps in redundancy. Therefore, continually assess your network’s needs for better failover solutions.

UplinkFast is designed only for access layer switches. It does not work for distribution or core layers. This limitation affects your network’s redundancy.

If you use devices in other layers, explore different methods. Additionally, complex network setups might not benefit from UplinkFast. As a result, you could face gaps in redundancy.

Therefore, continually evaluate your network’s needs. This helps you find better failover solutions. Lastly, consider the risk of introducing issues with UplinkFast.

UplinkFast can increase the load on the switch. First, it rapidly changes ports from blocking to forwarding states. This action creates extra processing demands.

As a result, there is a greater risk of errors and glitches. This risk is especially true in busy environments. Furthermore, the added strain can lead to degraded network performance.

This issue is most noticeable during failover scenarios. Overall, users should be cautious about these impacts.

Lastly, relying on proprietary features like UplinkFast can be tricky. If your organization uses devices from different vendors, this may cause issues.

Cisco-specific features can complicate interoperability. Each vendor has a unique way to handle loop protection. As a result, performance may vary across different devices. Therefore, network planners should carefully consider these factors.

UplinkFast can improve STP efficiency in some cases. However, careful planning is essential. Awareness of its limitations will help maintain a robust network.

Additionally, understanding potential drawbacks is crucial. This knowledge aids informed decisions about implementing UplinkFast. Overall, use it effectively for better network performance.

How to Enable It?

To turn on the backup connection on the switch, use this command in the switch’s global config mode.

Switch# conf t
Switch(config)# spanning-tree uplinkfast

Watch our YouTube video to get a better grasp of having extra connections!

Watch on YouTube

FAQ About UplinkFast and Backup Links

Why does a backup link wait 50 seconds in standard STP?

STP makes sure the network is stable before opening a port. The blocked port goes through listening and learning stages in order. Each stage takes 15 seconds.

In addition, the max age counter waits 20 seconds. The total time reaches 50 seconds. During this time, end devices are fully cut off from the network.

UplinkFast comes into play exactly at this point. It skips the listening and learning stages. It moves the blocked port directly to forwarding mode.

How does a blocked port move directly to forwarding mode?

The switch notices right away that the main link to the root is broken. It immediately activates the backup path on the blocked port. It completely skips the listening and learning states.

Because these two stages exist to prevent loop formation. But since the backup path is already blocked, there is no loop risk. The switch speeds up with this logic.

As a result, the cut time drops from 50 seconds to 3-5 seconds. Users do not suffer a disconnection. Server sessions are protected.

Why does this backup path accelerator not work in the core layer?

Cisco designed this feature only for the access layer. The topology is much more complex in the core layer. There are multiple backup paths and equal-cost routes.

A faulty acceleration in the distribution layer can lead to temporary loops. That is why Cisco put this limit on purpose. The feature is risky on devices close to the root bridge.

I suggest Rapid Spanning Tree for the core layer. RSTP works safely on all layers. It converges much faster with alternate and backup port concepts.

Will I have problems with different brand switches in a mixed network?

You definitely will. The backup path accelerator is specific only to Cisco devices. HP or Juniper switches do not recognize this command.

In a mixed setup, an STP mismatch happens. While the Cisco side makes a fast switch, the other side stays at standard time. An unbalanced convergence occurs.

In this case, the cleanest solution is to switch to RSTP. All vendors support this standard. Port roles and fast switch mechanisms work together.

Why does the switch’s processor struggle when enabled from the command line?

During the fast switch, the switch updates the MAC address table right away. It changes the port mapping of thousands of addresses. This process creates a sudden spike on the CPU.

This load is felt especially on dense access layers. The switch slows down temporarily. It queues some control packets.

Still, this situation is not permanent. The processor returns to normal within a few seconds. The risk is at an acceptable level.

How do I verify that the backup path is active after turning on this feature?

First, I run the ‘show spanning-tree uplinkfast’ command. In the output, I see that the feature is enabled. Statistics are also listed.

Then I check the port states with ‘show spanning-tree vlan’. I examine the backup port’s role and the transition counter. I read from here how fast it switched from blocked state to forwarding state.

Finally, I do a physical test. I unplug the main link cable. I verify with ping that the backup path takes over right away. I do not see even a single packet loss.

Conclusion

Using UplinkFast can make the Spanning Tree protocol work a bit better in our network. It’s a great idea to turn it on in the regular STP setup. Also, we suggest having the STP BackboneFast feature turned on.

What is Uplinkfast in Spanning Tree Protocol? | How It Works?