Home > Articles > Networking > Wireless/High Speed/Optical

  • Print
  • + Share This
This chapter is from the book

How Mesh Works

Mesh is a fairly complex feature that relies on a wireless routing protocol, Cisco Adaptive Wireless Path Protocol (AWPP), that allows the MAPs to determine the best parent to relay their traffic to the RAP.

AWPP is designed specifically for wireless mesh networking in that its path decisions are based on link quality and number of hops. AWPP is also designed to provide ease of deployment, fast convergence, and minimal resource consumption. AWPP takes advantage of the LWAPP/CAPWAP wireless LAN (WLAN), where client traffic is tunneled to the controller and hidden from the AWPP process. Also, the advanced radio management features in the LWAPP/CAPWAP WLAN solution are available to the wireless mesh network and do not have to be built into AWPP.

When a MAP comes up in a mesh network, the AP is authenticated (bridge authentication). Two possible security modes are available for the bridge authentication: Extensible Authentication Protocol (EAP) and Pre-Shared Key. There is a four-way handshake using this primary key to establish an Advanced Encryption Standard (AES) session. Next, the new AP establishes an LWAPP/CAPWAP tunnel to the controller and is authenticated against the MAC filter list of the controller.

The controller then pushes the bridge shared secret key to the AP via LWAPP/CAPWAP, after which it re-establishes the AES session with the parent AP.

As previously described, the wireless mesh bridges traffic between the MAPs and the RAPs. The traffic can be from wired devices being bridged by the wireless mesh or wireless client traffic that is encapsulated in LWAPP/CAPWAP-Data and LWAPP/CAPWAP-Control traffic from the MAPs.

The AES encryption is established as part of the MAP establishing neighbor relationships with other MAPs (bridge authentication). The bridge shared secret is used to establish unique encryption keys between mesh neighbors. All APs establish an LWAPP/CAPWAP connection to the controller through AES-encrypted backhaul tunnels between the APs.

Mesh Bootup and Join Process

When a mesh AP first boots up, it must determine whether it is a RAP. This decision-making process is as follows:

  • Step 1. Upon boot, an AP checks its state; if it is a RAP, it enters the Maintain state.
  • Step 2. If it is not a RAP, the AP scans all the channels for Bridge Group Names (BGN).
  • Step 3. The AP actively solicits neighboring APs (Seek state).
  • Step 4. The AP selects the best parent from the available list.
  • Step 5. The AP authenticates to the Mesh network.
  • Step 6. The AP then enters the Maintain state and is willing to respond to solicitations. Solicitation allows for faster convergence, leaving more time for data transfer.

Figure 15-4 illustrates the Mesh Machine state.

Figure 15-4

Figure 15-4 Mesh Machine State

A mesh AP become a RAP if it can communicate with an LWAPP/CAPWAP controller through its Ethernet interface. All 1500 and 1520 series mesh APs ship as MAPs. If the mesh AP is a RAP, it can go straight to the Maintain state. In the Maintain state, the mesh AP has established an LWAPP/CAPWAP connection to the controller, so it does not need to seek other APs; rather, it simply responds to solicitations. If the mesh AP is not a RAP, it starts a scan process where it scans all available channels and solicits information from other mesh APs.

This behavior has two main implications:

  • The RAP does not change channels; therefore, the channel used to build the mesh from a RAP is defined in the RAP configuration. By default, the RAP uses channel 161 if it is an outdoor AP.
  • The mesh is built from the RAP out, because initially only the RAP can respond to solicitations.

If the AP is not a RAP, it follows the state diagram in Figure 15-4 in the following modes:

  • Scan: The AP scans all the backhaul channels using mesh beaconing. This mechanism is similar to the 802.11 beaconing mechanisms used by wireless access networks, except the protocol frames conform to the AWPP frames on the backhaul. The frame used for beaconing is a broadcast NEIGHBOR_RESPONSE called NEIGHBOR_UPDATE and is sent unsolicited.

    Essentially, the network advertises NEIGHBOR_UPDATE frames so that new nodes can scan and quickly discover neighbors. The generation rule is that each RAP and MAP broadcast NEIGHBOR_UPDATE frames after being connected to the network (via a controller). Any neighbor updates with signal-to-noise ratios (SNR) lower than 10 dB are discarded. This process is called passive scanning.

    The AP looks for mesh beacons advertising the same BGN as what was configured on the AP when you primed it.

    If the AP hasn't been preconfigured or primed (joined to the controller on the wire, AP role, BGN set, and so on), or if the BGN it has been configured to is not seen in mesh beacons, the AP goes into default mode and proceeds with joining. This allows you to "catch" an AP in case of a config issue. Nevertheless, Cisco recommends that you always prime the APs with the BGN.

  • Seek: After the AP decides to join a mesh network it has located, bridge authentication takes place. This is done based on PSK or EAP. The AP solicits members of the mesh network. Successful responses to these solicitations become neighbors. These neighbors must have the same bridge group name and same shared secret.
  • Sync: The MAP learns the path information from each of its neighbors, and the neighbor with the greatest ease becomes the parent of the soliciting MAP. If the neighbors report multiple RAPs, the RAP with the greatest ease is chosen.
  • Authenticate: The MAP authenticates to the controller through a connection established through its parent AP. This AP authentication is standard LWAPP/CAPWAP AP authentication, and the MAP is already part of the mesh and using the mesh to communicate with its controller. Because MAPs are always in bridge mode, in addition to the standard LWAPP/CAPWAP authentication (bridge authentication during the Seek state), the controller requires mandatory MAC address authorization. Should you fail to add the AP's MAC address to the controller's MAC filter list (see Figure 15-6), the AP will not be able to proceed beyond the Authenticate state.
  • Maintain: The MAP responds to other MAP solicitations and regularly solicits to determine any changes in the mesh. It is only after entering the Maintain state that the MAP is visible to the controller and Wireless Control System (WCS). Note that in the Maintain state, the solicitations occur only on the channel defined by the RAP, whereas a MAP in seek mode solicits on all channels, only stopping when it has found a parent AP.

AWPP uses ease to determine the best path. Ease can be considered the opposite of cost, and the preferred path is the path with the higher ease.

Ease is calculated using the SNR and hop value of each neighbor and applying a multiplier based on various SNR thresholds. The purpose of this multiplier is to apply a spreading function to the SNRs that reflects various link qualities.

In Figure 15-5, MAP2 prefers the path through MAP1 because the adjusted ease (436906) though this path is greater than the ease value (262144) of the direct path from MAP2 to RAP.

Figure 15-5

Figure 15-5 Mesh Parent Selection

A parent AP is chosen by using the adjusted ease, which is the ease of each neighbor divided by the number of hops to the RAP:

480equ01.jpg

So in Figure 15-5, the adjusted case for MAP2 through MAP1 is 873812/2 = 436906.

Configuring Mesh

Configuring the controller to support mesh is quite simple. All you need to do is add the MAC address of the mesh AP to the MAC Filter list of the controller (see Figure 15-6). For 152x outdoor mesh APs, use the Bridge-Group Virtual Interface (BVI) MAC address of the mesh AP. For 1130 and 1240 series indoor mesh APs, you would use the Ethernet MAC address. If you do not know the MAC of the AP and it is not on the exterior of the unit, you can use the console to determine the BVI and Ethernet MAC addresses using the command sh int | i Hardware. You can also run debug pm pki enable from the controller command-line interface (CLI) to see the MAC address of the AP that is trying to join, as demonstrated in Example 15-1. The description for the AP in the MAC filter list is simply a text string you enter; it has nothing to do with actually configuring the AP.

Figure 15-6

Figure 15-6 MAC Filter List for MAPs

Example 15-1. debug pm pki enable Command Output

Fri Jul 10 17:55:37 2009: spamMeshRadiusProcessResponse: AP Authorization failure
for 00:0b:85:6f:9b:90

If the APs' MAC address is not listed, the AP fails authentication and cannot join the controller. This is true for both the indoor and outdoor mesh APs. When the AP rejoins the controller, set its role to be either a RAP or MAP (see Figure 15-7) using the Mesh tab. For the indoor APs, change the AP mode to Bridge and reboot it (see Figure 15-8) before you can configure the mesh-specific settings. When the AP reboots in bridge mode, you see the Mesh tab on the AP configuration page.

Figure 15-7

Figure 15-7 Mesh AP Role

Figure 15-8

Figure 15-8 Indoor Mesh Bridge Setting

The Mesh tab is where you will set the AP role as well as the BGN and backhaul data rates. This is true for both outdoor and indoor MAPs.

You can use the BGN to break large mesh deployments into sectors so that only certain APs will form parent-child relationships.

By default, the security mode for bridge authentication is EAP. This is done using manufacturer-installed certificates and therefore does not need configuring. Should you want to change the security mode to PSK or use a RADIUS server to authenticate the mesh APs, you can configure those settings from the controller GUI under Wireless > Mesh, as shown in Figure 15-9.

Figure 15-9

Figure 15-9 Mesh Bridge Security Configuration

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020