HP 9304m Installation And Getting Started Manual page 187

Installation and Getting Started Guide
Customer and SP Use Multiple Spanning Trees
Figure 6.3 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 6.3 Customer and SP using multiple spanning trees
tagged to multiple vlan
stp-boundary
untagged to vlan 100
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 6.4 shows an example of SuperSpan where the customer network uses multiple spanning trees while the
SP network uses Single STP.
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R
10
1/1
Customer
Region
3/1
R
20
R
xx
Root bridge for VLAN xx
2/2
R
100
2/1
Provider
Region
2/1
R
2/2
200