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Personal Cisco > Wireless Roaming & Location Services > Flashcards

Wireless Roaming & Location Services Flashcards

1
Q

Causes of Roaming

A

1) Maximum retries exceeded
2) Low RSSI
3) Low SNR
4) Proprietary roaming parameters

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2
Q

Active Scan

A
  • occurs when a client changes its 802.11 radio to the channel that is being scanned, broadcasts a probe request, and then waits (usually ~ 10ms) to hear any probe responses (or periodic beacons) from APs on that channel (with a matching SSID)
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3
Q

Directed Probe

A

the client sends a probe request with a specific destination SSID; only APs with a matching SSID reply with a probe response

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4
Q

Broadcast Probe

A
  • the client sends a broadcast SSID (actually a null SSID) in the probe request; all APs receiving the probe request respond with a probe response for each SSID they support
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5
Q

Passive Scan

A
  • performed by changing the 802.11 radio of the client to the channel that is being scanned and waiting for a periodic beacon from any APs on that channel.
  • by default, APs send beacons every ~100ms, so most client prefer an active scan
  • during a channel scan, the client is unable to transmit or receive client data traffic
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6
Q

Background Scanning

A
  • clients can scan available channels before they need to roam
  • this scan builds knowledge of the RF environment and available APs so clients can roam faster if it becomes necessary
  • minimize impact by only scanning when the client is not actively transmitting data, or by periodically scanning only a single alternate channel at a time (bc scanning a single channel incurs minimal data loss)
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7
Q

On-roam scanning

A
  • occurs when a roam is necessary
  • everyone has their own algorithms to minimize roam latency
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8
Q

Roam Algorithm Factors

A

1) Client data type (e.g. “voice call in progress”
2) Background scan information

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9
Q

Scan Algorithm Factors

A

1) Scan a subset of channels
2) Terminate the scan early
3) Change scan timers

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10
Q

Mobility Group

A
  • a collection of mobility controllers (MCs) across which roaming needs to be supported
  • can consist of up to 24 WLCs that share the context and state of client devices and WLC loading info
  • wireless client can roam btwn any AP in a mobility group without needing to authenticate
  • client info is transferred if it moves to another WLC
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11
Q

Mobility Domain

A
  • when a WLC can recognize WLCs that belong to another mobility group, the WLCs are said to be in the same domain
  • up to 3 separate mobility groups can be cross-populated into each other’s mobility lists to form a mobility domain and support up to 72 controllers
  • to be in the same domain, the built-in MAC and mgmt IP of each controller has to be entered in the other controller
  • to transmit mobility control msgs, Cisco WLCs use UDP 16666 for unencrypted traffic
  • user data is transmitting via EoIP (IP protocol 97) or CAPWAP (UDP 5246) tunnels
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12
Q

Mobility Group Required Commonalities

A

1) Mobility domain name
2) Version of controller code
3) CAPWAP mode
4) ACLs
5) WLANs (SSIDs)

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13
Q

WLC Client Database Information

A

1) MAC and IP of the client
2) Security context and associations
3) QoS contexts
4) WLAN
5) associated AP

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14
Q

Layer 2 Roaming

A
  • occurs when the client moves from one AP to another and is maintained in the same VLAN
  • Intracontroller Roaming - controller updates the client database with the newly associated AP
  • Intercontroller Roaming (L2) - the new controller exchanges mobility msgs with the original controller, and the client database entry is copied to the new controller
  • if necessary, new security context, and associations are established
  • remains transparent to user unless 1) client sends a DHCP discover request, or 2) the session timeout is exceeded
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15
Q

L2 Intercontroller Roaming Prerequisites

A
  • involved WLCs are L2 adjacent, share the VLAN info, and are in the same mobility group. they share SSIDs that are mapped to the same VLAN and subnet
  • compatible version of AireOS code in centralized deployments, and the controller is both the MC and MA
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16
Q

L2 Intercontroller Roaming Steps

A

1) Initially, the POP and PoA are colocated on teh same controller
2) The user roams to another AP and its associated WLC
3) The new controller exchanges mobility msgs with the original controller, and the client db entry is moved to the new controller (same mobility group)
4) New security context and associations are established if necessary, and the client database entry is updated for the new AP
5) The entire mobility context (POP and PoA) of the client is moved
6) The client traffic is also moved to the new path

17
Q

L3 Roaming

A
  • occurs when the client moves from an SSID on one AP (that is associated with one VLAN and respective IP subnet) to the same SSID on a different AP (that is associated with a different VLAN and IP subnet).
18
Q

L3 Intercontroller Roaming

A
  • share the same SSID, but are mapped to different VLANs
19
Q

L3 Intercontroller Roaming Steps

A

1) Initially, the POP and the PoA of the user are colocated on the same controller
2) The user roams from an AP and its associated controller (anchor) to another AP and its associated controller (foreign)
3) The new controller exchanges mobility msgs with the original controller, and the client database entry is copied to the new controller (same mobility group)
4) New security context and associations are established if necessary, and the client database entry is updated for the new AP
5) The client PoA is moved to the new controller (foreign)
6) The client POP stays fixed to the original controller (anchor). This is done to ensure that the user retains the same IP across an L3 boundary roam, and ensure continuity of policy application during roaming
7) The client traffic is tunneled back to the original controller (anchor). This is called symmetric mobility tunneling.

20
Q

Roaming with Auto-Anchor Mobility (Guest Access)

A
  • aka Guest tunneling
  • is a subset of a mobility group in which all of the client traffic that belongs to a WLAN (typically Guest WLAN) is tunneled to a predefined WLC or set of controllers that are configured as an anchor for that specific WLAN.
  • helps to restrict clients to a specific subnet and have more control over user traffic
21
Q

Auto-Anchor Mobility Uses

A

1) To limit guest access to the corporate network by first passing the traffic through the firewall
2) To implement a geographic access policy that can restrain client traffic to a specific subnet, no matter where the client is physically located
3) To change roaming characteristics if a firewall prevents L3 roaming from functioning properly

22
Q

Auto-Anchor Process

A

1) The wireless client associates to an AP on WLC1 on a guest SSID
2) The guest user PoA will be with WLC1 that is associated through
3) WLC1 will be pointed to the guest anchor for the guest SSID
4) The guest user traffic will be tunneled to the guest anchor WLC via either EoIP or CAPWAP
5) The guest user IP will come from the guest anchor.
6) The guest anchor becomes the POP for the guest, and will staty static
7) The guest, once authenticated (assume WebAuth on the guest anchor), will have its traffic de-encapsulated at the anchor WLC and moved out to the network
8) The wireless client roams to an AP on WLC2, which points to the same guest SSID on the guest anchor
9) The guest user PoA is now with WLC2
10) The guest user POP is still with the guest anchor
11) The guest user traffic will be tunneled from WLC2 to the guest anchor WLC

23
Q

Cisco Connected Mobile Experiences (CMX) Features

A

1) Detect - presence or location-based detection using the Wi-Fi signal. can provide location accuracy from 10m all the way down to 1m of accuracy (with Hyperlocation module and antenna array attached). Can also provide a location that is based on Bluetooth low energy (BLE), which requires BLE modules to be installed in the venue
2) Connect - provide a customized portal for guests to log into the network. Could have the user authenticate with a password, or their social media account to gather more data
3) Engage - provide content to the guests, such as coupons

24
Q

Dwell time

A
  • the time that the devices spend in a venue
25
Q

CMX Analytics Tools

A

1) Presence Analytics - counting devices; repeat vs new visitors, or passer-by vs visitor
2) Location Analytics - heatmaps provide a visual representation of total activity on a floor map

26
Q

Location Accuracy

A
  • 20m | In-zone detection | Venue-level visitors, dwell time | at least 1 AP
  • 7m | X,Y coordinates | Zone-level correlation | Minimum 3 APs, map integration
  • 5m | Optimized refresh | Subzone-level navigation | Increased AP density, FastLocate enabled
  • 1m | Highly accurate | Product placement, asset mgmt | Modular APs with Hyperlocation module

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