Misconfiguration Of Dhcp; Identifying The Node Exclusion Algorithm - Cisco Mesh Access Points Deployment Manual

Troubleshooting
applies if you relocate equipment. For example, if you uninstall a mesh access point and redeploy it in another
physical location of the mesh network that has a different addressed subnet.
Another option is to take a controller in Layer 2 mode with a RAP to the location with the misconfigured
MAP. Set the bridge group name on the RAP to match the MAP that needs the configuration change. Add
the MAP's MAC address to the controller. When the misconfigured MAP comes up in the mesh access point
summary detail, configure it with an IP address.

Misconfiguration of DHCP

Despite the DHCP fallback mechanism, there is still a possibility that a mesh access point can become stranded,
if any of the following conditions exist:
• There is no DHCP server on the network.
• There is a DHCP server on the network, but it does not offer an IP address to the AP, or if it gives a
These conditions can strand a mesh access point that is configured with or without a wrong static IP address
or with DHCP. Therefore, you must ensure that when a mesh access point is unable to connect after exhausting
all DHCP discovery attempts or DHCP retry counts or IP gateway resolution retry counts, it attempts to find
a controller in Layer 2 mode. In other words, a mesh access point attempts to discover a controller in Layer
3 mode first and in this mode, attempts with both static IP (if configured) or DHCP (if possible). The AP then
attempts to discover a controller in Layer 2 mode. After finishing a number of Layer 3 and Layer 2 mode
attempts, the mesh access point changes its parent node and re-attempts DHCP discovery. Additionally, the
software exclusion-lists notes the parent node through which it was unable to obtain the correct IP address.

Identifying the Node Exclusion Algorithm

Depending on the mesh network design, a node might find another node "best" according to its routing metric
(even recursively true), yet it is unable to provide the node with a connection to the correct controller or correct
network. It is the typical honeypot access point scenario caused by either misplacement, provisioning, design
of the network, or by the dynamic nature of an RF environment exhibiting conditions that optimize the AWPP
routing metric for a particular link in a persistent or transient manner. Such conditions are generally difficult
to recover from in most networks and could blackhole or sinkhole a node completely, taking it out from the
network. Possible symptoms include, but are not limited to the following:
• A node connects to the honeypot but cannot resolve the IP gateway when configured with the static IP
• A node ping-pongs between a few honeypots or circles between many honeypots (in worst-case scenarios).
Cisco mesh software resolves this difficult scenario by using a sophisticated node exclusion-listing algorithm.
This node exclusion-listing algorithm uses an exponential backoff and advance technique much like the TCP
sliding window or 802.11 MAC.
The basic idea relies on the following five steps:
1 Honeypot detection—The honeypots are first detected via the following steps:
A parent node is set by the AWPP module by:
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wrong IP address to the AP (for example, on a wrong VLAN or subnet).
address, or cannot obtain the correct IP address from the DHCP server, or cannot connect to a WLAN
controller.
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