Meraki Mesh Netwoking

By | December 6, 2018

Meraki Mesh Networking

Meraki Mesh is easy but it can be tricky at a time in my recent deployment, which was a point to multipoint. Below are some tricks to make sure they come up fast.

  1. Have your AP’s (Gateway AP and Repeater AP’s) added to your network?

2. On Dashboard configure the Static channels (not DFS), Power (based on Site survey) or Auto, correct Antennas and most important add Tags. **if you don’t have tags repeater have a very tough time finding Gateway.

3. Make sure Mesh is enabled

4. Check the spectrum from the gateway to make sure the channel you are using is clean.

Now in this process getting our setup working below were some details that we collected from Meraki support and system engineers so would like to credit them for the information shared.

In a mesh network, access points can be in one of two states: Gateway, or Repeater.

Gateways

Gateway access points are connected directly to the wired network, granting it an uplink to the Internet. If a gateway loses its Internet connection, it will look for a nearby gateway and automatically fail over to acting as a repeater, allowing it to continue serving clients.

Meraki determines whether a device should be a repeater or a gateway on boot, when the unit sends out a DHCP request. If it receives a DHCP reply from a device on the wired network, it assumes that it has a valid LAN connection and will become a gateway AP. If a gateway AP is unable to reach the LAN gateway/upstream router, the AP will fail over to repeater mode.

Repeaters

Repeater access points are not directly connected to the wired network, instead relying on wireless mesh links to reach the Internet. As long as the repeater has power and a
strong (unobstructed, line-of-sight) wireless connection to another repeater or gateway, it will form a mesh link.

Please note, it is not possible to configure a static IP address for a repeater AP; doing so will automatically designate the device as a gateway instead of a repeater.
Both gateways and repeaters can serve wireless clients. It is possible to have multiple gateways in a mesh network, and repeaters will automatically choose the gateway to which it has the strongest connection.

Mesh Process Node Discovery

  • Discovery Probes are periodically sent out by the APs.
  • They are sent out in various sizes and bitrates.
  • The AP scans all channels to collect info from all neighbors.

Selecting a Gateway

A Repeater may have multiple Gateways as neighbors. The best Gateway link is computed to determine the best neighbor and that neighbor will be marked as the Gateway. These metrics include:

  • ETT Stat Measurement. (Expected Transmission Time)
  • Trip time for various frame sizes
  • Packet Loss
  • Prefer nodes in the same network
  • Signal strength
  • SNR
  • Hops
  • Network ID (will try to find the APs in the same Network) .

Gateway selection does not:

  • Prefer an AP with better capabilities
  • Have any tunable configurations

Mesh selections can be influenced using power control and antenna positions or static channel assignments.

Bitrate Selection

  • MRs exchange information about their capabilities:
    • Supported bitrates
    • Frame aggregation
  • Meraki Proprietary bitrate selection algorithms are used during Mesh Communication.
  • Meraki uses the lowest bit rate to ensure the APs have a valid neighbor to account for worse case. Mesh Communication
  • Once a Gateway is selected mesh communication starts.

All information in the mesh link is encrypted, and the keys are managed by the Meraki dashboard.

Mesh Timers

Time taken to determine gateway is down:
• If a gateway is not reachable for 3 minutes, the repeater will mark the gateway as down.

Timer for the repeater to start looking for new gateway:

  • The repeater will start looking for a new gateway immediately after gateway is marked as down.
  • The AP starts scanning for new gateways. Will scan the entire spectrum (including 2.4 GHz and 5 GHz) and then select the best one that is available based on metric.
  • Higher preference is given to the configured channel.

Timer to start evaluating for new gateway when already connected:

  • The repeater will only evaluate on channels currently being used.
  • Repeater AP will check constantly but each AP will send mesh info every 15 seconds onthe channel currently being used.

How often does the repeater AP look for better gateways?

  • Always (Every 15 seconds)

If a better gateway is found what is the threshold to move to the new gateway?

  • If a new gateway appears and has a better metric even by 1 than the existing gateway AP, the repeater will move to that gateway

If an existing data flow is being used would we change the gateway?

  • Yes. Once the link is established the new gateway is confirmed after 5 seconds.

If yes, what happens to the existing gateway?

  • The existing link will be used for the 5 seconds before moving to the new gateway.

How can the repeaters and gateways be influenced to mesh quicker?

  • The gateway and repeater can be manually assigned to operate on the same channel so priority is given to building a mesh link on that channel. Using the behavior described above the setup can be planned.

Mesh FAQ

  • What happens when a repeater gets rebooted?
    The AP scans all channels to collect info from all neighbors. If a valid neighbor (inNetwork Meraki AP) is found, it goes to that channel. The configured channel has a higher precedence if a valid neighbor is found on it. If no valid neighbor is found on all channels it stays on the configured channel.
  • What happens when a repeater gets rebooted and does not detect the desired gateway? The repeater will build a mesh relationship with a less ideal gateway and will only move to a better gateway if both of the following criteria are met:
    a) the new gateway is operating on the same channel as the repeater b) the new gateway has a better metric than the existing gateway.

 

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