Alcatel-Lucent 7750 SR - Page 521

Virtual Private LAN Services
7750 SR OS Services Guide Page 521
Max Age
The max-age command indicates how many hops a BPDU can traverse the network starting from
the root bridge. The message age field in a BPDU transmitted by the root bridge is initialized to 0.
Each other bridge will take the message_age value from BPDUs received on their root port and
increment this value by 1. The message_age thus reflects the distance from the root bridge.
BPDUs with a message age exceeding max-age are ignored.
STP uses the max-age value configured in the root bridge. This value is propagated to the other
bridges via the BPDUs.
The default value of max-age is 20. This parameter can be modified within a range of 6 to 40,
limited by the standard STP parameter interaction formulae.
CLI Syntax: config>service>vpls service-id# stp
max-age max-info-age
Range:
6 to 40 seconds
Default: 20 seconds
Restore Default: no max-age
Forward Delay
RSTP, as defined in the IEEE 802.1D-2004 standards, will normally transition to the forwarding
state via a handshaking mechanism (rapid transition), without any waiting times. If handshaking
fails (e.g. on shared links, see below), 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 on page 531).
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:
•in
rstp mode, but only when the SAP or spoke SDP has not fallen back to legacy STP
operation, the value configured by the hello-time command is used;
• in all other situations, the value configured by the forward-delay command is used.
CLI Syntax: config>service>vpls service-id# stp
forward-delay seconds
Range:
4 to 30 seconds
Default: 15 seconds
Restore Default: no forward-delay