Configuring Access Guardian Bring Your Own Devices (BYOD) Overview
OmniSwitch AOS Release 8 Network Configuration Guide December 2017 page 28-128
Simple Service Discovery Protocol
The Digital Living Network Alliance (DLNA) is a standards organization that defines the guidelines for
multimedia devices. It also certifies communication between devices allowing them to discover and
recognize each other and share digital content. DLNA uses Universal Plug and Play (UPnP) for media
management, discovery, and control. DLNA/UPNP uses the Simple Service Discovery Protocol (SSDP) to
discover services, similar to Bonjour using mDNS for the same purpose. In the AirGroup solution, the
WLAN controller acts as Bonjour and DLNA gateways allowing Layer 2 discovery protocols, such as
mDNS and SSDP, to extend across Layer 3 boundaries through the gateway.
Along the lines of zero network configuration already supported by the OmniSwitch with mDNS, support
of SSDP Relay for DLNA/UPnP enables the OmniSwitch to allow non-Apple devices to also discover
services with minimal configuration by the administrator.
• DLNA/UPnP uses SSDP for dynamic discovery of services.
• The WLAN controller AirGroup feature has support for DLNA and acts as a DLNA controller, in
addition to the support for mDNS.
• Similar to the OmniSwitch implementation of mDNS, the OmniSwitch relays SSDP packets to the
WLAN controller through a Layer 2 GRE tunnel.
How SSDP Relay Works
All the SSDP packets coming in on an OmniSwitch are intercepted and tunneled through a GRE tunnel to
the WLAN controller (acting as a gateway). The GRE tunnel is setup between the switch and the WLAN
controller to tunnel both mDNS and SSDP frames. Similarly, traffic towards the SSDP clients/servers are
sent back from the WLAN controller to the switch through the GRE tunnel. The reverse traffic is also
intercepted and then sent unicast or multicast from the switch to the respective ports.
Messages Received by the OmniSwitch from Wired SSDP Devices
SSDP messages coming from wired SSDP service devices are relayed from the OmniSwitch to the WLAN
controller using the associated GRE tunnel interface. The WLAN controller only supports Layer 2 GRE
for SSDP, so frames sent from the OmniSwitch are encapsulated as follows:
Messages Received by the OmniSwitch from the WLAN Controller
SSDP messages coming from the WLAN controller through the Layer 2 GRE tunnel interface are relayed
towards the client device. When the OmniSwitch receives the encapsulated packets:
• The original SSDP frame is extracted from the GRE packet with the Layer 2 header.
• The switch obtains the VLAN ID from inside the 802.1Q header of the SSDP frame and floods the
frame on that VLAN (untagged or tagged based on the egress port frame) towards the client.
DA-MAC
Gateway MAC to reach
WLAN controller/
WLAN controller MAC
SA - MAC
OmniSwitch MAC
IP Header
Src IP: OmniSwitch IP
Dst IP: WLAN controller IP
IP protocol: GRE(47)
GRE VER 00 00
GRE TYPE 00 00 (indicating L2
frame in the payload)
Payload
SSDP frame from the
wired service/client
(appended with 802.1q
tag)
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