Cisco Cisco 5520 Wireless Controller Guide De Dépannage
This document provides information about the OTAP process.
The OTAP feature is enabled on the controller GUI from the controller General page or through the CLI with
the config network otap−mode {enable | disable} command.
the config network otap−mode {enable | disable} command.
Note: This feature is disabled by default and should remain disabled when all access points are installed.
The OTAP process begins when the LAP momentarily brings the radio interfaces up before the Discovery
phase and scans the different RF channels that listen for RRM neighbor packets. It is possible that the LAP
receives or does not receive an RRM neighbor packet on the first boot. This depends on:
phase and scans the different RF channels that listen for RRM neighbor packets. It is possible that the LAP
receives or does not receive an RRM neighbor packet on the first boot. This depends on:
How many LAPs are in the area (the greater the number of LAPs in the area, the greater the chance of
the LAP receiving an RRM neighbor packet)
the LAP receiving an RRM neighbor packet)
1.
How many channels are being used by Auto−RF (the more channels, the less likely the LAP is to
receive an RRM neighbor packet)
receive an RRM neighbor packet)
2.
How long the LAP scans the RF channels during the OTAP process (typical scan times before the AP
moves into the discovery phase are 18 to 35 seconds for all channels)
moves into the discovery phase are 18 to 35 seconds for all channels)
3.
When the LAP moves into the Discovery phase, it sends discovery requests through its primary interface to
each of the controllers in the lists based on how it learned about them. For the controllers that are learned
through OTAP, the LAP sends the controller a Discovery Request packet with the OTAP bit set. This
indicates to the controller that the AP learned its management IP address through OTAP. Other discovery
methods, such as DNS or DHCP option 43, are not differentiated in the Discovery Request packet because
they are learned through wired connections.
each of the controllers in the lists based on how it learned about them. For the controllers that are learned
through OTAP, the LAP sends the controller a Discovery Request packet with the OTAP bit set. This
indicates to the controller that the AP learned its management IP address through OTAP. Other discovery
methods, such as DNS or DHCP option 43, are not differentiated in the Discovery Request packet because
they are learned through wired connections.
This controller can reject discovery requests for these reasons:
The OTAP bit is set in the Discovery Request packet and OTAP is disabled on the controller.
1.
The Discovery Request packet is too large.
2.
The Discovery Request packet is not received on the management interface.
3.
LAPs support OTAP only when they have a full LWAPP Cisco IOS image. OTAP is not supported by the
LWAPP Recovery Cisco IOS image. The LWAPP Recovery Image is shipped from the factory and loaded by
the upgrade tool. The recovery images (cXXXX−rcvk9w8−mx), shipped with new outof−the−box LAPs, do
not contain any radio firmware and do not bring up any radio interfaces during the boot process. Hence OTAP
does not work with out−of−the−box LAPs. The exceptions are out−of−the−box 1510s and 1520 APs, which
have a full image installed in flash.
LWAPP Recovery Cisco IOS image. The LWAPP Recovery Image is shipped from the factory and loaded by
the upgrade tool. The recovery images (cXXXX−rcvk9w8−mx), shipped with new outof−the−box LAPs, do
not contain any radio firmware and do not bring up any radio interfaces during the boot process. Hence OTAP
does not work with out−of−the−box LAPs. The exceptions are out−of−the−box 1510s and 1520 APs, which
have a full image installed in flash.
Note: OTAP enabled on the controller indicates to the controller whether or not to respond to discovery
requests with the OTAP bit set. It does not prevent the LAPs already joined to the controller from the
transmission of the management IP address of the controller in the clear in RRM neighbor packets. Thus, if
you disable OTAP on the controller, this does not disable it on the access point. OTAP cannot be disabled on
the access point.
requests with the OTAP bit set. It does not prevent the LAPs already joined to the controller from the
transmission of the management IP address of the controller in the clear in RRM neighbor packets. Thus, if
you disable OTAP on the controller, this does not disable it on the access point. OTAP cannot be disabled on
the access point.
Radio Resource Management (RRM) Neighbor Packets
OTAP utilizes RRM neighbor packets. This section provides a brief background on RRM neighbor packets.
LAPs already joined to a controller transmit RRM neighbor packets to the RRM multicast address
01:0b:85:00:00:00. Each LAP must transmit a Neighbor Discovery packet once every 60 seconds on each of
the configured Auto−RF channels for 802.11b/g and 802.11a. The RRM neighbor packets are transmitted
without any encryption similar to other RF management packets, such as probe requests and probe responses.
The RRM neighbor packets contain neighbor control messages. See the RRM Neighbor Packet for 802.11a
section for more information. Each neighbor control message consists of:
LAPs already joined to a controller transmit RRM neighbor packets to the RRM multicast address
01:0b:85:00:00:00. Each LAP must transmit a Neighbor Discovery packet once every 60 seconds on each of
the configured Auto−RF channels for 802.11b/g and 802.11a. The RRM neighbor packets are transmitted
without any encryption similar to other RF management packets, such as probe requests and probe responses.
The RRM neighbor packets contain neighbor control messages. See the RRM Neighbor Packet for 802.11a
section for more information. Each neighbor control message consists of: