Brocade Multi-Service IronWare Switching Configuration Guide (Supporting R05.6.00) - Manual (Page 520)

490 Multi-Service IronWare Switching Configuration Guide
53-1003036-02
MRP Phase 2
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FIGURE 115 Example 1 multiple rings sharing interfaces - phase 2
On each node that will participate in ring 1, you configure the ring ID and the ring interfaces that
will be used. You repeat the configuration steps for all nodes in ring 2. In a multiple ring
configuration, a ring’s ID determines its priority. The lower the ring ID, the higher the priority of a
ring with ring ID 1 being the highest possible priority.
A key concept with MRP phase 2 is the ability to extend a single vlan across the whole topology
even when multiple rings are required. Consider the example in
Figure 116 where we have 3 MRP
rings and a customer who needs to create neighbor relationships between all three routers
depicted. The routers all have interfaces configured in a single subnet and need IP connectivity
between each other.
If each ring had an independent vlan then we would have to have a mechanism to move IP packets
from a single IP subnet between different layer 2 topologies. By using MRP phase 2 we have
multiple rings all associated with a single layer 2 topology allowing a common subnet to be
distributed in the manner shown in the example. Whilst this looks nothing like a standard spanning
tree network it should be treated in the same way from the perspective of a layer 2 topology,
multiple paths where certain paths must be blocked to prevent loops at layer 2.
In addition it should be noted that the concept of multiple rings being associated with a single vlan
describes the extent to which broadcasts will be propagated at layer 2 for that vlan. In other words
a broadcast will be propagated to all ring interfaces in the layer 2 topology. The use of topology
groups allows multiple vlans to effectively reuse a single layer 2 topology while maintaining a level
of separation.
The obvious issue with this approach is that there must be a mechanism to prevent loops on the
rings and this is the job of MRP, layer 2 loop prevention.