DNAC latency to Managed Devices ?

[trandinh]

Hi experts ,

I m planning for DNAC deployment and  I know that the  WAN latency between DNAC to  reach managed devices is 250ms.

Im not sure it is tolerable to proceed or it is impossible.

Thank you

[Damien Miller]

Imran's guide here covers latency best practices. The recommendation was 100ms RTT, where up to 200ms could be possible but not ideal.  
https://community.cisco.com/t5/networking-documents/cisco-sda-design-guidance-and-best-practices/ta-p/3865954

The same guidance is provided here
https://community.cisco.com/t5/networking-documents/cisco-sd-access-for-distributed-campus-with-ip-as-a-transit/ta-p/3837284

[jedolphi]

250ms is outside the limits of what we publicly endorse as of right now, May 2020, but it  might change later. Please see the PDF here for official limits -> https://community.cisco.com/t5/networking-documents/cisco-sda-design-guidance-and-best-practices/ta-p/3865954 . In some circumstances we allow to exceed the limits in that PDF but it requires a discussion with your technical presales team please. Best regards, Jerome

[jedolphi]

Ah, Damien beat me to it. Cheers :)

[Redman1804]

I have a query that coincides with this discussion.

Since 2020, I notice that the permitted latency between DNAC and FE has increased as indicated by Jerome i.e. it's gone up to 200ms from 100ms.

This has allowed me to go forward with proposing a multi-site SDA solution for a customer to replace their legacy traditional networking environment. However, whilst about 95% of the edge devices are within the 200ms limit, a handful of small sites are outside the limit. I intend to discuss with Cisco presales as advised but from the perspective of being aware and fully informed of potential technical risk and then accepting and signing off on those risks, what are the actual potential issues that affect FEs further away than 200ms.

I suspect SWIM updates might be an issue  but affected FEs could be treated as exceptions and updated manually as a workaround. Also, will the potential issues be restricted to only those devices outside the 200ms  limit or could they affect the entire fabric

Thanks

[tpoulose]

See the Latency Considerations section of the SDA Design Guide url provided below.

Latency considerations

Fabric access points operate in local mode. This requires a RTT (round-trip time) of 20ms or less between the AP and the Wireless LAN Controllers. This generally means that the WLC is deployed in the same physical site as the Access Points. If dedicated dark fiber exists between the physical sites and the WLCs in the data center and the latency requirement is meant, WLCs and APs may be in different physical locations. This is commonly seen in metro area networks and SD-Access for Distributed Campus. APs should not be deployed across the WAN from the WLCs. Cisco DNA Center 3-Node Clusters must have a RTT of 10ms or less between nodes in the cluster. For physical topology options and failover scenarios, please see Cisco DNA Center 3-Node Cluster High Availability scenarios and network connectivity detailstechnote. Latency in the network is an important consideration for performance and the RTT between Cisco DNACenter and any network device it manages should be taken into account. The optimal RTT should be less than 100 milliseconds to achieve optimal performance for Base Automation, Assurance, Software-Defined Access, and all other solutions provide by Cisco DNA Center. The maximum supported latency is 200ms. Latency between 100ms and 200ms is supported, although longer execution times could be experienced for certain events including Inventory Collection, Fabric Provisioning, SWIM, and other process

https://www.cisco.com/c/dam/en/us/td/docs/solutions/CVD/Campus/sda-sdg-2019oct.pdf