"Packet Loss threshold" option in "Performance SLAs"

[damianhlozano]

Hello team!!!

When I configure a new "Performance SLA", in the "Packet Loss threshold" option I can set the maximum packet loss to consider a link as "Up" but I dont know how many time or cheks are used to get the value.

I mean, with a low value, it is more likely to fail if the amount of time or cheks is little, so I need to know this, but I did not find any relative document.

Could you help me?

Thanks in advance.

Regards,

Damián

[pjawalekar]

Hi damianhlozano,

The Link Status section of the performance SLA configuration consists of three settings that determine the frequency that the link is evaluated, and the requirements to be considered valid or invalid:

• Check interval: the interval in which the FortiGate checks the interface, in milliseconds (500 - 3600000, default = 500).
• Failures before inactive: the number of failed status checks before the interface shows as inactive (1 - 3600, default =5). This setting helps prevent flapping, where the system continuously transfers traffic back and forth between links.
• Restore link after: the number of successful status checks before the interface shows as active (1 - 3600, default = 5). This setting also helps prevent flapping.

You can refer to the below KB article which describes how  Performance SLA - SLA targets will work:

https://docs.fortinet.com/document/fortigate/7.4.0/administration-guide/867342/performance-sla-overv...).

Regard's,

Pratik

[damianhlozano]

Hello Pratik,

Thanks for your answer!!!

This KB article is very nice, but I get not answer to my question, not in your answer nor in this article.

My question is about "Packet Loss threshold", What period of time does this percentage use?

Thanks in advance.

Regards,

Damián

[kkhushdeep]

Hello Damian,

FortiGate calculates and reports packet loss as a percentage of packets lost relative to the total number of packets sent.
The absolute number of packets lost will depend on the total traffic volume during the monitoring period.
FortiGate doesn't typically specify this in terms of an absolute number of packets.

(Number of packets with loss) / (Total number of packets in the monitoring period) = Packet loss percentage

You can set Check interval: the interval in which the FortiGate checks the interface, in milliseconds (500 - 3600000, default = 500).
and Packet loss threshold: packet loss for SLA to make a decision, in percentage (0 - 100, default = 0).

FortiGate monitors the packet loss as a ratio, and when it exceeds 1%, it will trigger actions defined in your SD-WAN rule.

Thanks

Khushdeep

[damianhlozano]

Hello Khushdeep,

Thanks for your answer, however I still couldnt get it.

Which is this "monitoring period"?

• If this is the time since the first check, when I created the SLA, the amount of checks are a lot and I will need a lot of packets lost to reach 1%

• If this is the time since the last check, I think there are no checks between.

Is there something I am missunderstanding or there is lack of documentation?

Thanks in advance.

Regards,

Damián

[damianhlozano · Accepted solution]

Hello team,

In the case someone else want to know, I opened a ticket and finally they give me a link with this information.

• Latency threshold: Calculated based on last 30 probes (default = 5ms).

• Jitter threshold: Calculated based on last 30 probes (default = 5ms).

• Packet Loss threshold: Calculated based on last 100 probes (default = 0%).

https://docs.fortinet.com/document/fortigate/7.4.0/administration-guide/580649/link-health-monitor

Regards!

Damián