Quick Reference Guide
PowerConnect B-Series TI24X Configuration Guide 207
53-1002269-02
Metro Ring Protocol (MRP)
8
When the broken link is repaired, the link interfaces come up in the Preforwarding state, which
allows RHPs to travel through the restored interfaces and reach the secondary interface on the
master node:
• If an RHP reaches the master node secondary interface, the ring is intact. The secondary
interface changes to Blocking. The master node sets the forwarding bit on in the next RHP.
When the restored interfaces receive this RHP, they immediately change state to Forwarding.
• If an RHP does not reach the master node secondary interface, the ring is still broken. The
master node does not send an RHP with the forwarding bit on. In this case, the restored
interfaces remain in the Preforwarding state until the preforwarding timer expires, then change
to the Forwarding state.
If the link between shared interfaces breaks (Figure 41), the secondary interface on Ring 1 master
node changes to a preforwarding state. The RHP packet sent by port 3 on Ring 2 is forwarded
through the interfaces on S4, then to S2. The packet is then forwarded through S2 to S3, but not
from S2 to S1 since the link between the two nodes is not available. When the packet reaches Ring
1 master node, the packet is forwarded through the secondary interface since it is currently in a
preforwarding state. A secondary interface in preforwarding mode ignores any RHP packet that is
not from its ring. The secondary interface changes to blocking mode only when the RHP packet
forwarded by its primary interface is returned.
The packet then continues around Ring 1, through the interfaces on S1 to Ring 2 until it reaches
Ring 2 master node. Port 4, the secondary interface on Ring 2 changes to blocking mode since it
received its own packet, then blocks the packet to prevent a loop.
FIGURE 41 Flow of RHP packets when a link for shared interfaces breaks
RHP packets follow this flow until the link is restored; then the RHP packet returns to it normal flow
as shown in Figure 39.
X
Ring 1
Ring 2
S3
S4
S1
S2
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
1,2
1,2
Master node
P
ort2 changes
to preforwarding
(primary interface)
P
ort1
Master node
Port4
P
ort3 (primary interface)
= Ring 2 RHP packet
T
T