The radio frequency channels on non-root bridges changes while it roams and associates with a different root bridge

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Wed, 11/18/2009 - 18:20
Jun 22nd, 2009
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Core Issue


The BR 350 dynamically changes radio frequency (RF) channels when it pulls into a station and associates with a different root bridge when it roams only if it is set to the non-root mode.


Resolution

The root bridges stay on the frequency they are configured for and do not change frequency, though there is an exception. If the search for less congested channel option is enabled, each time the bridge or access point restarts, it quickly scans all available channels and picks the one that is the least congested at that time.

These are a few important items to know about the bridges:


  • When mobility applications use bridges, disable the spanning tree. This allows the negotiation to occur faster.

  • The non-root bridges allow the With/Clients option and a Bridge Only option. In the Bridge Only mode, the non-root bridges simply deny the wireless clients that attempt to register. The root bridges, the 350 series, do not have this Bridge Only mode. They automatically allow the clients to register.

  • The site survey (antenna alignment) utility on the 350 bridges lacks polish and has room for improvement. It works, but only the non-root units can align to a root unit. In other words, the alignment starts at the non-root device.

  • The 340 series bridges are not compatible with the 350 series bridges. They use different spanning trees and run different operating systems. The older 340 bridge uses Aironet proprietary code and the 350 series runs Wind River VxWorks. There are slight differences in the way they communicate over the Radio Frequency (RF) and the spanning tree. For example, the 340 uses the Aironet proprietary spanning tree while the 350 uses an implementation of the Cisco spanning tree over wireless. These differences make these two different series of bridges incompatible at this time. The preliminary tests show that a root 340 bridge allows a non-root 350 bridge to communicate and pass data, but it is not recommended. No regression tests exist, and it does not work in reverse order. Therefore, it is recommended to keep the bridges the same series if at all possible.

  • Sometimes a non-root 350 bridge cannot obtain an IP address. This is mostly resolved, but sometimes, during the spanning tree negotiation, the request from the non-root 350 bridge for an IP address gets lost. The fix forces the unit to ask again.

  • In site survey client mode bridge surveys Repeater AP. In this mode, the bridge can connect to another bridge or AP, but it does not accept client associations.

  • Hot standby mode is supported only when a bridge is configured as an AP. With hot standby, the AP becomes a client and attaches to another AP that it monitors to as a client. When the unit that it monitors fails, the AP pulls itself out of client mode and becomes the primary.

  • In order for any two bridges or access points to communicate with each other, one must be a root and the other bridges or APs must be set to non-root. The non-root radio devices actively seek out and connect to the root units, based upon the SSID.

  • The antenna alignment occurs from the non-root device to the root device.

  • The Ethernet port of an access point in non-root mode is disabled, so access points do not bridge wired segments. Only the bridge series products actually bridge wired LANs. The access points in non-root mode simply allow clients to jump through them and use them as a repeater.

Refer to these documents for more information:



Problem Type


Product information

Interference issues ( EMI / RF issues)


Products


Bridge

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