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Feature Friday: Inline Flow Performance Monitoring

  • 1.  Feature Friday: Inline Flow Performance Monitoring

    Posted 10-25-2022 10:08

    Hey everyone!

    Halloween is only a week away. Time to get in your last Halloween movies, figure out what costumes you are going to wear, and buy candy for the trick-or-treaters. For those that don't know what "trick-or-treaters" are, these are the kids (and adults in my case) who go door to door on Halloween asking for a treat (usually candy). By saying "trick-or-treat" they are actually threatening to do some mischief on you if you don't give them a treat. 

    It's kind of like they are threatening you if you don't give them a good quality service…reminds me of how the Session Smart Router can monitor and ensure SLAs for your traffic with Inline Flow Performance Monitoring ensuring great quality for you and your customers.

    That's right everyone, for today's Feature Friday we are going to look at Inline Flow Performance Monitoring!!!!

    Ok, so what is Inline Flow Performance Monitoring and how does it guarantee that my traffic will have great quality? Well, let's start with how the SSR measures path quality without Inline Flow Performance Monitoring.

    Out of Band Flow Performance Monitoring

    Prior to Inline Flow Performance Monitoring being added to the Session Smart Router (which happened in release 5.0), the SSR could still measure the quality of its Peer Paths. You may remember, Peer Paths are the connections from 1 SSR to another (aka a Peer). This measurement was done using BFD in Echo Mode. You ever notice when you look at the traffic on your Peer Paths that you see traffic going back and forth with source and destination port 1280? That's your BFD traffic. That is used for many reasons, including making sure the Peers are up and detecting if there are any TCP stateful firewalls that could cause you some trouble. It is also used in Echo Mode to detect the quality of the path.

    Echo mode messages are transmitted from one router to its Peer, which simply echoes them back to the originating router. The messages are then read by the originating router to determine Jitter, Loss, and Latency. Jitter is determined by how bunched up the packets are, Loss by how many packets made it back to the originating router, and Latency by how long it took for those packets to come back to the originating router. If both Peers use the default BFD settings, you should expect to see each router independently perform Echo Mode tests every 10 seconds, consisting of 10 Echo Mode packets sent to its Peer in rapid succession, for each Peer Path it has established with that Peer. Upon receipt, the Peer will echo them back to the originating router.

    You can learn more about BFD and how to tune your settings by checking out this document: 

    Inline Flow Performance Monitoring

    The Echo Mode version of performance monitoring works great for when you want to know how the paths are performing, even when there is no traffic going across them. HOWEVER, you have probably seen times when VoIP or video traffic is treated differently than BFD. This becomes a headache because you get complaints from your customers that the network sucks even though everything is telling you it looks fine.

    That is where Inline Flow Performance Monitoring comes in!

    Inline Flow Performance Monitoring complements BFD in measuring Peer Paths between two SSR devices. To provide this additional level of detail, the initiating router adds a small amount of metadata to a sample number of packets. This metadata indicates that metrics are collected per path, traffic class, and transport protocol (TCP or UDP). The receiving router reads the metadata and returns the data to the initiating router.

    The information gathered is organized by traffic class (high, medium, low, best-effort) and transport protocol (TCP, UDP). I'll go over more on traffic class and traffic engineering in a future Feature Friday. This gives you a better picture on the performance of the link by looking at the real traffic being sent, not just the BFD going back and forth.

    Now, you may ask: "…wait, Justin, in your FF on Secure Vector Routing (Part 1 and Part 2), you mentioned that you only add metadata during the session setup. Now you are saying metadata is added here for the Inline Flow Performance Monitoring???"

    You are correct, it is additional metadata being added. However, it is only a very small amount of metadata and you can configure how often you want to include it with the marking-count and interval-duration settings. This is all configured at the neighborhoods/adjacencies, so you can have different settings for different paths. Check out this document to learn more about the metadata:

    Here is where you can find the official documentation on configuring Inline Flow Performance Monitoring:

    Path Failover Due to SLA

    Ok, cool, you can see how your paths are doing with live traffic and without traffic. But what can you do with that information?

    You can now have path failover occur using this information! It's configured in the Service Policy. Just set a failover strategy (failover/revertible failover) and put in your Jitter, Loss, Latency, or MOS thresholds. If traffic is traversing a path that exceeds one of these thresholds, the traffic will failover to the other path. The SSR will use data from both the "Out of Band Flow Performance Monitoring" and the "Inline Flow Performance Monitoring" when checking these thresholds. Because this is set at the Service Policy, that means you can have different thresholds for different applications.

    With this feature, you no longer have to worry about the CEO calling you up to complain about the quality of their conference call. This also is just one of the powers that the SSR has that can make you an SD-WAN Hero! Oh! Maybe a Super Hero costume is what you should wear for Halloween!

    For more information, check out this blog on Inline Flow Performance Monitoring written by Patrick Melampy: 

    Alright, now I want to hear from you:

    • Are you using Inline Flow Performance Monitoring?
    • If so, how has your experience been with it?
    • Have you adjusted your BFD settings or are you using the default?
    • I am still trying to figure out my Halloween costume. Do you have any suggestions?

    I hope you all have a great and safe Halloween! Don't get haunted or tricked and I will see you in November.

    #FeatureFridays #MeetSD-WANHero #SSR #BFD #SLA #Failover #MOS #metadata #ServicePolicy


    Justin Melloni