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Cisco Viptela SDWAN: Packet Duplication

March 24, 2023 ,

Cisco Viptela SDWAN: Packet Duplication

Have you ever experienced choppy audio or video during a meeting or presentation? Or maybe your boss has complained about slow application performance? These issues can be frustrating and can severely impact your work productivity. That's where packet duplication comes in.

💻 Table Of Content

What is Packet duplication ?

Packet duplication is the process of replicating packets and transmitting them through several pathways in a network at the same time. The goal of packet duplication is to increase network application reliability and performance by guaranteeing that at least one duplicate of the packet reaches the destination, even if other packets are lost or delayed in route.

Packet duplication can be accomplished in a variety of ways, including using network devices that support it natively or by building specific software programs that duplicate packets. In some circumstances, such as WAN optimization, packet duplication may be done as part of a larger network traffic optimization plan.

Cisco Viptela SDWAN & Packet Duplication

Cisco Viptela SD-WAN offers a packet duplication feature that can improve the delivery of mission-critical applications. When enabled, this feature sends two identical copies of a packet across different paths, ensuring that at least one copy reaches the destination. This is especially important for applications such as voice and video, where even a small amount of packet loss or delay can cause major disruptions.

Cisco Viptela SDWAN: Packet Duplication
Fig 1.1-Cisco Viptela SDWAN: Packet Duplication

Packet duplication can be configured on a per-policy basis, allowing you to customize the feature based on your specific needs. You can define criteria such as source/destination IP addresses, protocols, port numbers, and more. 

The vEdge routers in the SD-WAN overlay network inspect the packets as they pass through and make a copy of the packet if it meets the criteria defined in the policy. The copy of the packet is then forwarded across a different path from the original packet to the destination.

However, it's important to use packet duplication judiciously. This feature can increase network traffic and utilization, leading to higher costs and potential congestion issues. It's recommended to use packet duplication only for mission-critical applications and to carefully tune the policies to avoid unnecessary duplication.

Let's say you're working remotely from home, and you need to attend an online meeting with your team. You join the meeting expecting a seamless experience, but you hear choppy audio and see blurry video. Frustrated, you try to reconnect but still experience the same issues. This is where packet duplication can save the day. 

By enabling this feature for your voice and video applications, you can ensure that your packets are delivered across different paths, reducing the risk of packet loss and ensuring a smooth experience.

Benefits of Packet Duplication

Improved reliability: By duplicating packets and delivering them through several pathways, packet duplication can help to ensure that at least one copy of the packet reaches the destination even when there is network congestion, packet loss, or other difficulties. This can increase the dependability of mission-critical applications that demand excellent network performance and uptime.

Improved performance: By reducing the likelihood of packet loss and retransmission, packet duplication can help to improve the performance of network applications, particularly those that are sensitive to network latency and delays, such as voice and video applications.

Enhanced network resiliency: Packet duplication can assist to improve network resilience by providing redundant channels for traffic, which can help to reduce network downtime and guarantee business continuity in the case of network failures or other interruptions.

Greater flexibility: Packet duplication can be implemented on a per-application or per-policy basis, which provides greater flexibility in network management and optimization. This allows network administrators to tailor packet duplication to the specific needs of different applications and workloads, and to optimize network performance accordingly.

Remember, packet duplication is just one of the many features offered by Cisco Viptela SD-WAN to optimize network performance. By utilizing this feature, you can ensure that your mission-critical applications are delivered seamlessly, providing a better user experience for you and your team.

Enabling packet duplication

Enabling packet duplication for a specific application is as simple as configuring one command, loss-protection packet-duplication under the data policy rule that matches the application traffic. However, before you start duplicating packets left and right, there are a few details to consider to make sure everything runs smoothly.

First, there must be at least two overlay tunnels between the sending and receiving WAN edge router. This ensures that your data can be sent across multiple paths, reducing the risk of data loss.

Second, it's important to enable the packet duplication capability only for well-defined critical traffic. Don't put it under any match-all rules, because it can quickly exhaust the CPU of a WAN edge router. We want to avoid bogging down the router with unnecessary packet duplication.

Finally, remember to enable packet duplication in both directions separately. This ensures that your data is being sent and received securely and without any hiccups.

With these details in mind, you can easily enable packet duplication for your critical traffic, ensuring that your data is delivered safely and securely. Here you can see the sample configuration under data policy.

policy
 data-policy DATA-POLICY-TO-CAMPUS
  vpn-list NDNA
   sequence 51
    match
     protocol 1
    !
    action accept
     loss-protection packet-duplication
       set
       local-tloc color mpls encapsulation ipsec
     !
     default-action accept
     !

Verify using below command
NDNA-vEdge# show tunnel statistics packet-duplication

Conclusion

To summarize, the Packet Duplication functionality prevents packet loss for key applications such as voice at the price of higher bandwidth use. The following traits are associated with the feature:

  • It works with any transport protocol, including TCP and UDP.
  • Works only over multiple tunnels.
  • On the receiver, duplicates are eliminated.