Specifications

208 ExtremeWare XOS 11.0 Concepts Guide
Spanning Tree Protocol
Figure 21: VLANs traverse domains inside switches
• The VLAN partition feature is deployed under the premise that the overall interdomain topology for
that VLAN is loop-free. Consider the case in Figure 22, VLAN red (the only VLAN in the figure)
spans STPDs 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 22: 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.
EX_052
S1
WrongCorrect
S2
S2
S1
EX_053
Domain 3
Domain 2
Domain 1