Alcatel-Lucent 7750 SR Manual page 480

Discovery Procedures
A PE router issues an access-request to the RADIUS server using the configured VPN as the user-
name and configured password. The service type of the access request is L2VPN.
The RADIUS server authenticates the PE router. If authentication is successful, it responds with
an access-accept which includes a list of IP addresses of the PE routers. Optional information such
as vc-type and SDP could be included. If authentication fails, an access-reject message is returned.
The access-accept response has a session-timeout attribute in which a PE router needs to issue a
new access-request before the access-accept times out.
Auto SDPs and SDP-Bindings Creation
After the discovery of all other PE routers, the PE router checks if it has valid auto SDP bindings
for remote PE routers. Manual SDPs always take precedence over auto SDPs. If there was a
manual SDP available, it is used to create the auto SDP binding; otherwise, the PE router creates
auto SDPs and auto SDP bindings. If there were multiple SDPs available for a PE router, the SDP
with the smallest SDP ID is used.
What auto-SDP to create, LDP or GRE, depends on the RADIUS configuration, default is GRE.
When an auto SDP is created for a remote PE router and there is no targeted LDP session to the PE
router, a targeted LDP session is automatically created.
Pseudo-Wire Setup
The PE routers use "AII" as the VC-ID (pseudowire ID) to signal pseudowires to each other by
targeted LDP.
RADIUS Server Polling
A PE router should periodically query the RADIUS server to make sure its L2VPN membership
information is up-to-date. The polling interval is configurable by CLI.
Any change to the VPN membership (such as adding or removing a PE) takes effect at the next
polling.
Page 480 7750 SR OS Services Guide