APAR Discovery

1
AP/AR Discovery

• CAPWAP BOF
• IETF-57, Vienna
• Inderpreet Singh
• isingh_at_chantrynetworks.com

2
Discovery Requirements

• Scalability
• 100s of APs per AR
• Multiple ARs
• Minimal administration
• Speed
• msecs per discovery?
• Minimize code size of protocol/mechanism
• Work in general topologies
• on-subnet (switches)
• off-subnet (multiple router hops)
• Service Availability (robustness)

3
Discovery Steps

• Discovery
• AR IP address
• Capabilities (protocols supported, link speed,
  etc)
• Bootup discovery
• Dynamic discovery
• Service Availability
• Fault tolerance

4
Potential Solutions

• SLP based discovery
• Service Location Protocol
• RFC 2608
• RFC 2609
• RFC 2610
• DHCP based discovery
• New vendor specific option
• Static Config
• No brainer
• Scalability issues

5
SLP Based discovery (Unicast)
DHCP server
DA
network
AP
AR

• AR/SA registers service with DA
• Looks up location of DA with DHCP Option 78/79
• Statically configured DA location
• AP/UA looks up location of service with DHCP
  Option 78/79
• Needs to get IP address anyway from DHCP
• AP/UA contacts DA with service-type WLAN
• AP attempts to connect to AR for WLAN services
  (continues with discovery/join process)

6
SLP Based Discovery (Multicast/Bcast w/ no DA)
AP
multicast
multicast
unicast
AP
AR
L2 switch
multicast
unicast

• AP (or UA) issues multicast svr. request
• AR (or SA) issues unicast svr. response
• AP continues with discovery/join process

7
SLP based discovery

• Advantages
• Works with on or off subnet topologies
• AR addition to network is also automatic
  (registers with DA)
• Disadvantages
• SLP deployment in existing networks
• AP assignment to ARs is not automatic may
  require admin intervention

8
DHCP options for AP/AR Discovery
DHCP server
network
AP
AR

• AP sends DHCP-inform for WLAN AR option
• DHCP server responds with IP address of AR
• AP proceeds with discovery/join process

9
DHCP based discovery

• Advantages
• AP already has DHCP code (maybe?), needs to just
  be changed with DHCP options
• Works in L2 and L3 (need DHCP relay)
• Disadvantage
• Admin overhead for adding ARs to system
• Admin overhead to assign specific APs to
  specific ARs

10
Next steps

• Other requirements
• I-D for Discovery
• If SLP based then best practices draft?
• If DHCP based then option draft
• If other then other draft