BigIron RX Series Configuration Guide
BigIron RX Series Configuration Guide
v02.9.00a
Part Number: 53-1002484-04
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Configuring Spanning Tree Protocol : SuperSpan™

SuperSpan™
SuperSpan is an Brocade STP enhancement that allows Service Providers (SPs) to use STP in both SP networks and customer networks. The SP devices are Brocade devices and are configured to tunnel each customers' STP BPDUs through the SP. From the customer's perspective, the SP network is a loop-free non-blocking device or network. The SP network behaves like a hub in the sense that the necessary blocking occurs in the customer network, not in the SP.
The Brocade interfaces that connect the SP to a customer's network are configured as SuperSpan boundary interfaces. Each SuperSpan boundary interface is configured with a customer ID, to uniquely identify the customer's network within SuperSpan.
Figure 34 shows an example SuperSpan implementation. In this example, an SP's network is connected to multiple customers. Each customer network is running its own instance of standard STP. The Brocade devices in the SP are running SuperSpan.
Figure 34 SuperSpan example
In this example, the SP network contains two devices that are running SuperSpan. The SP is connected to two customer networks. Each customer network is running its own instance of STP. SuperSpan prevents Layer 2 loops in the traffic flow with each customer while at the same time isolating each customer’s traffic and spanning tree from the traffic and spanning trees of other customers. For example, the SP devices provide loop prevention for Customer 1 while ensuring that Customer 1’s traffic is never forwarded to Customer 2. In this example, customer 1 has two interfaces to the SP network, ports 1/1 and 1/2 connected to SP 1. The SP network behaves like a non-blocking hub. BPDUs are tunneled through the network. To prevent a Layer 2 loop, customer 1’s port 1/2 enters the blocking state.
Customer ID
SuperSpan uses a SuperSpan customer ID to uniquely identify and forward traffic for each customer. You assign the customer ID as part of the SuperSpan configuration of the Brocade devices in the SP. In Table 34, the spanning trees of customer 1 and customer 2 do not interfere with one another because the SP network isolates each customer’s spanning tree based on the SuperSpan customer IDs in the traffic.
BPDU forwarding
When a Brocade device receives a customer's BPDU on a boundary interface, the device changes the destination MAC address of the BPDU from the bridge group address (01-80-c2-00-00-00) as follows.
The first byte (locally administered bit) is changed from 01 to 03, to indicate that the BPDU needs to be tunneled.
The fourth and fifth bytes are changed to the customer STP ID specified on the boundary interface.
For example, if the customer's STP ID is 1, the destination MAC address of the customer's BPDUs is changed to the following: 03-80-c2-00-01-00.
Each Brocade device that is configured for SuperSpan forwards the BPDU using the changed destination MAC address. At the other end of the tunnel, the Brocade device connected to the customer's network changes the destination MAC address back to the bridge group address (01-80-c2-00-00-00).
Preforwarding state
To ensure that the customer's network has time to converge at Layer 2 and prevent loops, the Brocade devices configured for SuperSpan use a special forwarding state, Preforwarding. The Preforwarding state occurs between the Learning and Forwarding states and by default lasts for five seconds. During the Preforwarding state, the Brocade device forwards tunneled BPDUs from customers only and does not forward data traffic. This ensures that the customer’s network will detect the Layer 2 loop and block a port. The SP network remains unblocked. After the Preforwarding state, the Brocade ports change to the Forwarding state and forward data traffic as well as BPDUs.
The default length of the Preforwarding state is five seconds. You can change the length of the Preforwarding state to a value from 3 – 30 seconds.
Figure 35 shows an example of how the Preforwarding state is used.
Figure 35 SuperSpan preforwarding state
In this example, a customer has two links to the SP. Since the SP is running SuperSpan, the SP ports enter the Preforwarding state briefly to allow the customer ports connected to the SP to detect the Layer 2 loop and block one of the ports.
NOTE: If you add a new device to a network that is already running SuperSpan, you must enable SuperSpan on the new device, at least on the VLANs that will be tunneling the customer traffic. Otherwise, the new device does not use the Preforwarding state. This can cause temporary loops in the network.
Mixing single STP and multiple spanning trees
You can use SuperSpan in any of the following combinations:
NOTE: All the combinations listed above are supported when the boundary ports joining the SP SuperSpan domain to the client spanning trees are untagged. For example, all these combinations are valid in super aggregated VLAN configurations. If the boundary ports are tagged, you cannot use Single STP in the client network in combination with multiple spanning trees in the SP SuperSpan domain.
The examples below are in super aggregated configuration scenarios.
Customer and SP use multiple spanning trees
Figure 36 shows an example of SuperSpan where both the customer network and the SP network use multiple spanning trees (a separate spanning tree in each port-based VLAN).
Figure 36 Customer and SP using Multiple Spanning Trees
Both the customer and SP regions are running multiple spanning trees (one per port-based VLAN) in the Layer 2 switched network. The customer network contains VLANs 10 and 20 while the SP network contains VLANs 100 and 200. Customer traffic from VLAN 10 and VLAN 20 is aggregated by VLAN 100 in the SP since the boundary ports, 2/1 on R100 and R200, are untagged members of VLAN 100. By adjusting the bridge priority on VLANs 10 and 20, the customer can select a different root bridge for each spanning tree running in the customer network.
In the above example, STP in VLAN 10 will select R10 as the root bridge and make 1/1 on R10 forwarding while blocking port 3/1 on R20. The opposite occurs for STP in VLAN 20. As a result, both links connecting the customer and SP regions are fully utilized and serve as backup links at the same time, providing loop-free, non-blocking connectivity. In the SP network, multiple STP instances are running (one for VLAN 100 and one for VLAN 200) to ensure loop-free, non-blocking connectivity in each VLAN.
SuperSPAN boundaries are configured at port 2/1 of R100 and R200. Since the customer’s traffic will be aggregated into VLAN 100 at the SP, the SP network appears to the customer to be a loop-free non-blocking hub to the customer network when port 2/2 on R200 is blocked by STP in VLAN 100.
Customer uses multiple spanning trees but SP uses single STP
Figure 37 shows an example of SuperSpan where the customer network uses multiple spanning trees while the SP network uses Single STP.
Figure 37 Customer using Multiple Spanning Trees and SP using single STP
Customer traffic from different VLANs is maintained by different spanning trees, while the SP network is maintained by a single spanning tree. The SP can still use multiple VLANs at the core to separate traffic from different customers. However, all VLANs will have the same network topology because they are all calculated by the single spanning tree. The loop-free, non-blocking network acts like a hub for the customer network, with boundary ports 2/1 on each device being untagged members of VLAN 100.
Traffic from all VLANs in the customer network will be aggregated through VLAN 100 at the SP. This setup leaves the customer network’s switching pattern virtually unchanged from the scenario in “Customer and SP use multiple spanning trees”, since the SP network still is perceived as a virtual hub, and maintenance of the hub's loop-free topology is transparent to the customer network.
Customer uses single STP but SP uses multiple spanning trees
Figure 38 shows an example of SuperSpan where the customer network uses Single STP while the SP uses multiple spanning trees.
Figure 38 Customer using single STP and SP using Multiple Spanning Trees
In this setup, the customer network is running a single spanning tree for VLANs 10 and 20. The traffic from VLAN 10 and 20 will be carried, or aggregated by VLAN 100 at the SP’s network. The main difference between this scenario and the previous two scenarios is that all traffic at the customer’s network now follows the same path, having the same STP root bridge in all VLANs. Therefore, the customer network will not have the ability to maximize network utilization on all its links. On the other hand, loop-free, non-blocking topology is still separately maintained by the customer network’s single spanning tree and the SP’s per-VLAN spanning tree on VLAN 100.
Customer and SP use single STP
Figure 39 shows an example of SuperSpan where the customer network and SP both use Single STP.
Figure 39 Customer and SP using single STP
In this setup, both the customer and SP networks are running a single spanning tree at Layer 2. The traffic from VLAN 10 and 20 will be carried, or aggregated by VLAN 100 at the SP network as in the previous scenario. Loop-free, non-blocking topology is still separately maintained by the customer's single spanning tree and the SP's single spanning tree.
Configuring SuperSpan
To configure a device for SuperSpan:
Configuring a boundary interface
To configure the boundary interfaces on SP 1 in , enter the following commands.
BigIron RX(config)# interface ethernet 1/1
BigIron RX(config-if-e1000-1/1)# stp-boundary 1
BigIron RX(config)# interface etehrnet 1/2
BigIron RX(config-if-e1000-1/2)# stp-boundary 2
 
These commands configure two interfaces on the Brocade device as SuperSpan boundary interfaces. Interface 1/1 is a boundary interface with customer 1. Interface 1/2 is a boundary interface with customer 2. Each boundary interface is associated with a number, which is the SuperSpan ID. The SuperSpan ID identifies the instance of SuperSpan you are associating with the interface. Use the same SuperSpan ID for each boundary interface with the same customer. Use a different SuperSpan ID for each customer. For example, use SuperSpan ID 1 for all the boundary interfaces with customer 1 and use SuperSpan ID 2 for all boundary interfaces with customer 2.
Syntax:
[no] stp-boundary <num>
The <num> parameter specifies the SuperSpan ID. You can specify a number from 1 – 65535.
To configure the boundary interfaces on SP 2 in Figure 34, enter the following commands.
BigIron RX(config)# interface ethernet 2/1
BigIron RX(config-if-e1000-2/1)# stp-boundary 1
BigIron RX(config)# interface ethernet 2/2
BigIron RX(config-if-e1000-2/2)# stp-boundary 2
Enabling SuperSpan
After you configure the SuperSpan boundary interfaces, enable SuperSpan. You can enable SuperSpan globally or on an individual VLAN level. If you enable the feature globally, the feature is enabled on all VLANs.
NOTE: If you enable the feature globally, then create a new VLAN, the new VLAN inherits the global SuperSpan state. For example, if SuperSpan is globally enabled when you create a VLAN, SuperSpan also is enabled in the new VLAN.
You also can change the length of the Preforwarding state to a value from 3 – 30 seconds. The default is 5 seconds.
To globally enable SuperSpan, enter the following command.
BigIron RX(config)# super-span
 
Syntax:
[no] super-span [preforward-delay <secs>]
The <secs> parameter specifies the length of the Preforwarding state. You can specify from 3 – 15 seconds. The default is 5 seconds.
SuperSpan is enabled in all VLANs on the device. To disable SuperSpan in an individual VLAN, enter commands such as the following.
BigIron RX(config)# vlan 10
BigIron RX(config-vlan-10)# no super-span
 
Syntax:
[no] super-span
Displaying SuperSpan information
To display the boundary interface configuration and BPDU statistics, enter the following command.
In this example, the device has two SuperSpan customer IDs.
Syntax:
show superspan [cid <num>]
The cid <num> parameter specifies a SuperSpan customer ID. If you do not specify a customer ID, information for all the customer IDs configured on the device is shown.
This command shows the following information.
 
To display general STP information, refer to “Displaying STP information”.

Configuring Spanning Tree Protocol : SuperSpan™