Transcript PPT Version

AP/AR Discovery
CAPWAP BOF
IETF-57, Vienna
Inderpreet Singh
[email protected]
Discovery Requirements
• Scalability
– 100’s of AP’s per AR
– Multiple AR’s
– 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)
Discovery Steps
• Discovery
– AR IP address
– Capabilities (protocols supported, link speed,
etc)
• Bootup discovery
• Dynamic discovery
– Service Availability
– Fault tolerance
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
SLP Based discovery (Unicast)
DHCP
server
AR
1.
AP
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
a.
3.
4.
network
AR/SA registers service with DA
a.
b.
2.
DA
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)
SLP Based Discovery
(Multicast/B’cast w/ no DA)
AP
multicast
multicast
AR
unicast
L2 switch
unicast
AP
multicast
1. AP (or UA) issues multicast svr. request
2. AR (or SA) issues unicast svr. response
3. AP continues with discovery/join process
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 AR’s is not automatic – may
require admin intervention
DHCP options for AP/AR Discovery
DHCP
server
AR
network
AP
1. AP sends DHCP-inform for WLAN AR option
2. DHCP server responds with IP address of AR
3. AP proceeds with discovery/join process
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 AR’s to system
– Admin overhead to assign specific AP’s to
specific AR’s
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