secure mobility in cisco unified wlan networks for mobile devices
DESCRIPTION
Best practices for implementing the latest WLAN security techniques from design to deployment. Includes recommendations for proper authentication and encryption and fast secure roaming. Learn More: http://www.cisco.com/go/wirelessTRANSCRIPT
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Secure Mobility in Cisco Unified WLAN Networks BRKEWN-2018
Senior Manager/Architect, Technical Marketing
July 2011
Jake Woodhams
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Abstract
• The proliferation of Wi-Fi enabled devices creates important challenges for IT, perhaps the chief challenge being security and scalable, efficient, secure roaming. This session will cover the state-of-the-art technologies for proper authentication and encryption and fast, secure roaming. Topics include 802.11i/WPA/WPAv2, TKIP/AES & Fast roaming with CCKM, PKC, and the emerging 802.11r standard. Different EAP types like PEAP, PEAP-GTC, EAP-TLS, EAP-TTLS, EAP-FAST will be covered in this session. The session will include best practices for implementing latest WLAN security techniques and design and deployment recommendations for device roaming. Pre-requisite: A minimum of CCNA level knowledge of campus routing and switching is highly recommended. Knowledge of 802.11 WLAN fundamentals and the basics of the Cisco Unified WLAN technology are also assumed.
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Session Agenda
• Anatomy of a Device Connection • Anatomy of a Device Roam
• Design and Deployment Considerations
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Anatomy of a Device Connection
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Section Agenda
• 802.11 Architecture and Services Basics • 802.11i Addendum
• EAP Types and Key Management • Device Mobility Problem Statement
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802.11 Architecture Basics
BSS BSS
BSS – Basic Service Set
SSID – Service Set Identifier
BSSID – Basic Service Set Identifier
STA – Station (AKA Client)
STA STA
SSID: ASCII String BSSID: MAC Address
SSID: ASCII String BSSID: MAC Address
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802.11 Architecture Basics
ESS – Extended Service Set
DS – Distribution System
BSS BSS
ESS
DS
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802.11 Services Service Description Implementation
Distribution Services
STA Services
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802.11 Services Service Description Implementation
Distribution Services Association
Reassociation
Disassociation
STA Services
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802.11 Services Service Description Implementation
Distribution Services Association Used to create a logical connection between a mobile STA
and an AP 802.11
Reassociation
Disassociation
STA Services
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802.11 Services Service Description Implementation
Distribution Services Association Used to create a logical connection between a mobile STA
and an AP 802.11
Reassociation Similar to association service, except information about a mobile STA’s previous AP may be included; used as a STA moves across an ESS
802.11
Disassociation
STA Services
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802.11 Services Service Description Implementation
Distribution Services Association Used to create a logical connection between a mobile STA
and an AP 802.11
Reassociation Similar to association service, except information about a mobile STA’s previous AP may be included; used as a STA moves across an ESS
802.11
Disassociation Used by AP to force mobile STA off the BSS or by mobile STA to inform AP it doesn’t need service anymore 802.11
STA Services
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802.11 Distribution Services Association Service
802.11 Association Request: “Can I Associate to This BSSID?”
802.11 Association Response: “Yes, You Can Associate
to This BSSID”
802.11 Association Response: “No, You Cannot Associate
to This BSSID”
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802.11 Distribution Services Disassociation Service
802.11 Disassociation Request: “You Cannot Be Associated to This
BSSID Anymore”
802.11 Disassociation Request: “I Do Not Want to Be Associated to
This BSSID Anymore”
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802.11 Distribution Services Reassociation Service (Roaming Context)
802.11 Reassociation Request: “Can I Reassociate to This BSSID?”
802.11 Disassociation Request: “I Do Not Want to Be Associated to
This BSSID Anymore”
802.11 Association Response: “Yes, You Can Associate
to This BSSID”
802.11 Association Response: “No, You Cannot Associate
to This BSSID”
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802.11 Services Service Description Implementation
Distribution Services Association Used to create a logical connection between a mobile STA
and an AP 802.11
Reassociation Similar to association service, except information about a mobile STA’s previous AP may be included; used as a STA moves across an ESS
802.11
Disassociation Used by AP to force mobile STA off the BSS or by mobile STA to inform AP it doesn’t need service anymore 802.11
STA Services
So, What Do These Three Services Accomplish? What’s Missing?
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802.11 Services Service Description Implementation
Distribution Services Association Used to create a logical connection between a mobile STA
and an AP 802.11
Reassociation Similar to association service, except information about a mobile STA’s previous AP may be included; used as a STA moves across an ESS
802.11
Disassociation Used by AP to force mobile STA off the BSS or by mobile STA to inform AP it doesn’t need service anymore 802.11
STA Services Authentication Used to prove the identity of the STA and AP
WPA/WPAv2 (802.11I), CAPWAP
Deauthentication Used to eliminate a previously authenticated user from further use of the network
Privacy Used to protect frames in transit over wireless medium
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How STAs Connect to a WLAN Securely
• 802.11 spec defines authentication, deauthentication, and privacy services, but…
• 802.11 spec provides extremely weak (useless for 2010 requirements) mechanisms for these services:
- Authentication/Deauthentication: Shared-Key Auth
- Privacy: Wired Equivalent Privacy (WEP)
• 802.11I addendum adds strong(er) mechanisms for implementing STA security-related services:
- Authentication/Deauthentication: PSK, 802.1X/EAP
- Privacy: TKIP & CCMP
STA Services
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WPA/WPA2
• A snapshot of the 802.11I Standard • Commonly used with TKIP encryption WPA
• Final version of 802.11I • Commonly used with AES encryption WPA2
• Personal (PSK) – Home Use • Enterprise (802.1X/EAP) – Office Use
Authentication Mechanisms
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Authentication Best Practices: WPA2-Enterprise
• Extensible Authentication Protocol (EAP) • Outside Methods (Protective Tunnel):
• PEAP • EAP-FAST • TLS
• Inside Methods (Authentication Credentials): • EAP-MSCHAPv2 • EAP-GTC
Strong Authentication
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802.1X/EAP Choreography 802.1X/EAP Three Party Model
802.1X Port Blocking Instantiated: Only Authentication Transaction Related Traffic Allowed Through the AP
Keys Plumbed, 802.1X Port Blocking Removed… Data Allowed Through AP
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802.1X/EAP Choreography
Distribution Services: Association/Reassociation/Disassociation
STA Services: Authentication/Deauthentication
STA Services: Privacy
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EAP Types: EAP-FAST
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EAP Types: PEAP
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EAP Types: EAP-TLS
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802.1X/EAP Choreography
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Key Management – Four-Way Handshake
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Key Management – Pairwise Transient Key (PTK)
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Key Management – Group Transient Key (GTK)
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Key Management – GTK Distribution
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802.1X/EAP Choreography
Distribution Services: Association/Reassociation/Disassociation
STA Services: Authentication/Deauthentication
STA Services: Privacy
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802.11 Services Service Description Implementation
Distribution Services Association Used to create a logical connection between a mobile STA
and an AP 802.11
Reassociation Similar to association service, except information about a mobile STA’s previous AP may be included; used as a STA moves across an ESS
802.11
Disassociation Used by AP to force mobile STA off the BSS or by mobile STA to inform AP it doesn’t need service anymore 802.11
Distribution Service to determine how to deliver frames 802.11, CAPWAP
Integration Service to determine how WLAN connects to other LANs
STA Services Authentication Used to prove the identity of the STA & AP
WPA/WPAv2 (802.11I), CAPWAP
Deauthentication Used to eliminate a previously authenticated user from further use of the network
Privacy Used to protect frames in transit over wireless medium
Data Delivery Used to provide reliable delivery of frames 802.11, CAPWAP
So, What Do These Nine Services Accomplish? What’s Missing?
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802.11 Architecture Basics
ESS – Extended Service Set
DS – Distribution System
BSS BSS
ESS
DS ????
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802.1X/EAP Choreography
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Device Mobility Problem Statement: • Specification for how STAs association, authenticate, and protect data privacy defined in context of a single AP (mostly…) • Specifications for how STAs transition securely in an ESS – hazy • Specifics of DS/Integration services not well defined for Enterprise
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Device Mobility Problem Statement: • Wireless devices move by definition
• Applications require session persistence, while maintaining security and other services
Requirement: Facilitate Fast Secure Roaming for Enterprise Class Devices in an Efficient and Scalable Way…
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Anatomy of a Device Roam
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Section Agenda
• CUWN Architecture Review • Basic Roaming Walkthrough
• Fast Secure Roaming Technologies
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CUWN Architecture Review
Real-Time 802.11/MAC Functionality:
• Beacon Generation • Probe Response • Power management/Packet buffering • 802.11e/WMM scheduling, queueing • MAC layer data encryption/decryption • 802.11 control messages
Data Encapsulation/De-Encapsulation Translational Bridging (H-REAP Local Switching) Fragmentation/De-Fragmentation
Non Real-Time 802.11/MAC Functionality: • Assoc/Disassoc/Reassoc • 802.11e/WMM resource reservation • 802.1X/EAP • Key management
802.11 Distribution Services 802.11 STA Services (Auth/Deauth/Privacy*) Wired/Wireless Integration Services
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802.1X/EAP Choreography Revisited
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Anatomy of a STA Roam Initial Device Connection to Network
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Anatomy of a STA Roam Client Roam
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Anatomy of a STA Roam
• The STA chooses when to roam • Each time the STA connects to a new BSSID, it must fully
reauthenticate and rekey • IP Addresses get refreshed on roams (usually)
• How long does a roam take?
Summary of Important Points
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How Long Does an STA Roam Take?
• Time it takes for: Client to disassociate +
Probe for and select a new AP +
802.11 Association +
802.1X/EAP Authentication +
Rekeying +
IP address (re) acquisition
• All this can be on the order of seconds… Can we make this faster?
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How Are We Going to Make Roaming Faster? Focus on Where We Can Have the Biggest Impact…
Eliminating the (re)IP address acquisition challenge
Eliminating full 802.1X/EAP reauthentication
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Roaming: Intra-Controller
• Intra-controller roam happens when a STA moves association between APs joined to the same controller
• Client must be re-authenticated and new security session established
• Controller updates client database entry with new AP and appropriate security context
• No IP address refresh needed
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Roaming: Inter-Controller Layer 2
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Roaming: Inter-Controller
• L2 inter-controller roam: STA moves association between APs joined to the different controllers but client traffic bridged onto the same subnet
• Client must be re-authenticated and new security session established
• Client database entry moved to new controller
• WLCs must be in same mobility group or domain • No IP address refresh needed
• Account for mobility message exchange in network design
Layer 2
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Roaming: Inter-Controller Layer 3
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Roaming: Inter-Controller
• L3 inter-controller roam: STA moves association between APs joined to the different controllers but client traffic bridged onto different subnets
Client must be re-authenticated and new security session established
Client database entry copied to new controller – entry exists in both WLC client DBs
Original controller tagged as the “anchor”, new controller tagged as the “foreign”
WLCs must be in same mobility group or domain
No IP address refresh needed
Symmetric traffic path established -- asymmetric option has been eliminated as of 6.0 release
Account for mobility message exchange in network design
Account for asymmetric traffic path (EtherIP)
Layer 3
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How Are We Going to Make Roaming Faster? Focus on Where We Can Have the Biggest Impact…
Eliminating the (re)IP address acquisition challenge
Eliminating full 802.1X/EAP reauthentication
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Cisco Centralized Key Management (CCKM)
• Cisco introduced CCKM in CCXv2 (pre-802.11I), so widely available, especially with application specific devices (ASDs)
• CCKM originally a core feature of the “Structured Wireless Aware Network” (SWAN) architecture
• CCKM ported to CUWN architecture in 3.2 release
• In highly controlled test environments, CCKM roam times consistently measure in the 5-8 msec range!
• CCKM is most widely implemented in ASDs, especially VoWLAN devices
• To work across WLCs, WLCs must be in the same mobility group
• CCX-based laptops may not fully support CCKM – depends on supplicant capabilities
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PMKID Caching
• Optional component of 802.11I specification • Defines a “PMK Security Association” (PMKSA) that gets stored by
authenticator • PMKSA includes:
PMKID Lifetime PMK (32 bytes) BSSID (6 bytes) Client's MAC (6 bytes) AKM (Authentication and Key Management)
• PMKID =
HMAC-SHA1-128 (PMK, “PMK Name” || BSSID || STA Mac)
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Opportunistic/Proactive Key Caching
CAPWAP
802.11 Disassociation Request:
“I Do Not Want to Be Associated to
This BSSID Anymore”
1. WLC extracts PMKID from 802.11 (Re)association request
2. WLC computes the new PMKID based on the PMKSA and other information it knows (BSSID, Client Mac)
3. WLC compares the values – if they match, full 802.1X/EAP authentication is skipped and the WLC & client go directly to the four-way handshake, then updates the PMKSA in the client DB
4. If they don’t match, the WLC sends the STA an EAP-Identity Request to initiate the full 802.1X/EAP Authentication
Basic Mechanics
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Proactive Key Caching Basic Mechanics
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OKC/PKC
• Requires client/supplicant support • Supported in Windows since XP SP2
• Many ASDs support OKC and/or PKC • Check on client support for TKIP vs. CCMP – mostly CCMP
only
• Enabled by default on WLCs with WPAv2 • Requires WLCs to be in the same mobility group
• Important design note: pre-positioning of roaming clients consumes spots in client DB
• In highly controlled test environments, OKC/PKC roam times consistently measure in the 10-20 msec range!
Key Data Points
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Standardization! 802.11R
• 802.11R is a ratified IEEE standard, based in large part on CCKM
• 802.11R: “Fast (Basic Service Set) BSS Transition” • Also includes dynamic QoS capabilities
• No commercially available clients at this point
• WiFi Alliance is planning/implementing 802.11R plugfests • Cisco WLCs have implemented 802.11R (unsupported) since
5.2 • In highly controlled OTA test environments, 802.11R roam
times are comparable to CCKM OTA times
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How Are We Going to Make Roaming Faster? Focus on Where We Can Have the Biggest Impact…
Eliminating the (re)IP address acquisition challenge
Eliminating full 802.1X/EAP reauthentication
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Design and Deployment Considerations
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Section Agenda
• Roaming Domains • Design Considerations for Roaming
• Client Roaming Behavior • Special Case: H-REAP Groups
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Roaming Domains
• Mobility Group – cluster of up to 24 controllers (regardless of type) that create a seamless roaming domain
• Fast secure roaming technologies work across controllers within a roaming domain
• Mobility messages exchanged either unicast or multicast depending on configuration
Mobility Group
http://www.cisco.com/en/US/docs/wireless/controller/7.0/configuration/guide/c70mobil.html#wpmkr1100509
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Roaming Domains
• Mobility Domain is a seamless roaming domain of up to 3 Mobility Groups
• Max of 72 WLCs
• Seamless roaming == IP addressing is maintained
• Fast secure roaming does work not across Mobility Group – clients crossing these boundaries will have to go through a full reauth, but will retain their IP address
Mobility Domain
http://www.cisco.com/en/US/docs/wireless/controller/7.0/configuration/guide/c70mobil.html#wpmkr1100509
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How Long Does a Client Really Take to Roam?
• Time to roam = Client to disassociate +
Probe for and select a new AP +
802.11 Association +
Mobility message exchange between WLCs +
Reauthentication +
Rekeying +
IP address (re) acquisition
• Network latency will have an impact on these times – consideration for controller placement
• With a fast secure roaming technology, roam times under 150 msecs are consistently achievable, though mileage may vary
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How Often Do Clients Roam?
• It depends… types of clients and applications • Most client devices are designed to be “nomadic” rather than
“mobile”, though proliferation of small form factor, “smart” devices will probably change this…
• Nomadic clients usually are programmed to try to avoid roaming… so set your expectations accordingly
• “SWAG” design rule of thumb: 10-20 roams per second for every 5000 clients
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Designing a Mobility Group/Domain
• Less roaming is better – clients and apps are happier • While clients are authenticating/roaming, WLC CPU is doing
the processing – not as much of a big deal for 5508 which has dedicated management/control processor
• L3 roaming & fast roaming clients consume client DB slots on multiple controllers – consider “worst case” scenarios in designing roaming domain size
• Leverage natural roaming domain boundaries • Mobility Message transport selection: multicast vs. unicast
• Make sure the right ports and protocols are allowed
Design Considerations
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Special Case: FlexConnect Groups • Support for up to 20 FlexConnect Groups of up to 25
FlexConnect APs each
• APs in an FlexConnect share common configuration parameters like RADIUS servers
• Fast Secure Roaming via CCKM for locally switched clients is supported for all clients in an FlexConnect Group (L2 roaming only)
• CCKM keying material is provisioned locally – allows CCKM to work in standalone mode (existing clients when AP transitioned from connected mode)
* Note: FlexConnect is new branding for Hybrid REAP (H-REAP)
http://www.cisco.com/en/US/docs/wireless/controller/7.0/configuration/guide/c70hreap.html#wp1133688
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Questions?
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