Fast Port Span - Dell PowerConnect B-RX Configuration Manual

13
Configuring RSTP parameters
TABLE 79
Link speed
1 Gigabit per second
10 Gigabits per second
100 Gigabits per second
1 Terabits per second
10 Terabits per second
The priority <value> parameter specifies the preference that RSTP gives to this port relative to
other ports for forwarding traffic out of the topology. You can specify a value from 0 – 655352, in
increments of 4. If you enter a value that is not divisible by four the software rounds to the nearest
value that is. The default is 128 (the terminal shows this too). A higher numerical value means a
lower priority; thus, the highest priority is 8.
Set the admin-edge-port to enabled or disabled. If set to enabled, then the port becomes an edge
port in the domain.
Set the admin-pt2pt-mac to enabled or disabled. If set to enabled, then a port is connected to
another port through a point-to-point link. The point-to-point link increases the speed of
convergence. This parameter, however, does not auto-detect whether or not the link is a physical
point-to-point link.
The force-migration-check parameter forces the specified port to sent one RST BPDU. If only STP
BPDUs are received in response to the sent RST BPDU, then the port will go return to sending STP
BPDUs.
Suppose you want to enable RSTP on a system with no active port-based VLANs and change the
hello-time from the default value of 2 to 8 seconds. Additionally, suppose you want to change the
path and priority costs for port 5 only. To do so, enter the following commands.
BigIron RX(config)# spanning-tree 802-1w hello-time 8
BigIron RX(config)# spanning-tree 802-1w ethernet 5 path-cost 15 priority 64

Fast port span

When STP is running on a device, message forwarding is delayed during the spanning tree
recalculation period following a topology change. The STP forward delay parameter specifies the
period of time a bridge waits before forwarding data packets. The forward delay controls the
listening and learning periods of STP reconvergence. You can configure the forward delay to a
value from 4 – 30 seconds. The default is 15 seconds. Thus, using the standard forward delay,
convergence requires 30 seconds (15 seconds for listening and an additional 15 seconds for
learning) when the default value is used.
This slow convergence is undesirable and unnecessary in some circumstances. The Fast Port
Span feature allows certain ports to enter the forwarding state in four seconds. Specifically, Fast
Port Span allows faster convergence on ports that are attached to end stations and thus do not
present the potential to cause Layer 2 forwarding loops. Because the end stations cannot cause
forwarding loops, they can safely go through the STP state changes (blocking to listening to learning
to forwarding) more quickly than is allowed by the standard STP convergence time. Fast Port Span
performs the convergence on these ports in four seconds (two seconds for listening and two
seconds for learning).
388
Recommended path cost values of RSTP (Continued)
Recommended (default) RSTP path
cost values
20,000
2,000
200
20
2
Recommended RSTP path cost range
2,000 – 200,000,000
200 – 20,000
20 – 2,000
2 – 200
1 – 20
BigIron RX Series Configuration Guide
53-1002253-01