1. CAPWAP BOF IETF-57, Vienna Inderpreet Singh isingh@chantrynetworks.com
AP/AR Discovery
CAPWAP BOF
IETF-57, Vienna
Inderpreet Singh

2. 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)

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

4. Potential Solutions SLP based discovery DHCP 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 AR
network AP
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)
Advantage:Note that the AR automatically gets added to the DA. As new AR’s come on line, the service is automatically available to the existing AP’s.
Disadvantage: most probably there is administrative overhead to allocate AP’s to “specific” AR or ARs. In L2 multicast/broadcast this is not an issue….one AR per group of APs.

6. SLP Based Discovery (Multicast/B’cast w/ no DA)AP
multicast
multicast
unicast AR
L2 switch AP
unicast
multicast
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 Disadvantages
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

8. DHCP options for AP/AR Discovery
DHCP server AR
network AP
AP sends DHCP-inform for WLAN AR option
DHCP server responds with IP address of AR
AP proceeds with discovery/join process
In this case every time a new AR comes online the administrator must add that to the list of AR’s available in the DHCP server.

9. DHCP based discovery Advantages Disadvantage
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

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