Extreme Networks ExtremeWare XOS Guide Manual page 147

Figure 13: VLANs traverse domains inside switches
• The VLAN partition feature is deployed under the premise that the overall inter-domain topology
for that VLAN is loop-free. Consider the case in Figure 14, VLAN red (the only VLAN in the figure)
spans domains 1, 2, and 3. Inside each domain, STP produces a loop-free topology. However, VLAN
red is still looped, because the three domains form a ring among themselves.
Figure 14: Looped VLAN topology
A necessary (but not sufficient) condition for a loop-free inter-domain topology is that every two
domains only meet at a single crossing point.
ExtremeWare XOS 10.1 Concepts Guide
S1
S2
Correct
Domain 1
S1
S2
Wrong
Domain 2
Domain 3
STP Configurations
EX_052
EX_053
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