Forward Delay

RSTP, as defined in the IEEE 802.1D-2004 standards, normally transitions to the forwarding state by a handshaking mechanism (rapid transition), without any waiting times. If handshaking fails (for example, on shared links, as follows), the system falls back to the timer-based mechanism defined in the original STP (802.1D-1998) standard.

A shared link is a link with more than two Ethernet bridges (for example, a shared 10/100BaseT segment). The port-type command is used to configure a link as point-to-point or shared (see section SAP Link Type).

For timer-based transitions, the 802.1D-2004 standard defines an internal variable forward-delay, which is used in calculating the default number of seconds that a SAP or spoke-SDP spends in the discarding and learning states when transitioning to the forwarding state. The value of the forward-delay variable depends on the STP operating mode of the VPLS instance:

CLI syntax:

config>service>vpls service-id# stp 
forward-delay seconds
Range
4 to 30 seconds
Default
15 seconds
Restore Default
no forward-delay