Metro Ring Protocol Overview
Metro Ring Protocol (MRP) is a RUCKUS proprietary protocol that prevents Layer 2 loops and provides fast reconvergence in Layer 2 ring topologies. It is an alternative to the Spanning Tree Protocol (STP) and is especially useful in Metropolitan Area Networks (MAN) where using STP has the following drawbacks:
- STP allows a maximum of seven nodes. Metro rings can easily contain more nodes than this.
- STP has a slow reconvergence time, taking many seconds or even minutes. MRP can detect and heal a break in the ring in sub-second time.
The ring in Metro Ring - Normal Stateshows an example of the MRP metro ring, which consists of four MRP nodes (RUCKUS switches). Each node has two ring interfaces. Each node is also connected to a segment of the customer network. The nodes forward Layer 2 traffic between customer network segments through their ring interfaces, all configured in a port-based VLAN. Each customer interface can be in the same VLAN as the ring or in a separate VLAN through the use of topology groups.
One node is configured as the master node of the ring. One of the two interfaces on the master node is elected as the primary interface; the other is the secondary interface. The primary interface originates Ring Health Packets (RHPs), which are used to monitor the health of the ring. An RHP is forwarded on the ring to the next interface until it reaches the secondary interface of the master node. The secondary interface blocks the packet to prevent a Layer 2 loop.
MRP Master Switch Ring Interfaces and Configuration shows the master switch in an MRP topology, highlighting its primary (forwarding) and secondary (blocked) ring interfaces. The customer VLAN is VLAN 2 for which the ring is also configured in VLAN 2. The RHPs flow out the primary interfaces through the ring nodes arriving at the secondary interface to be discarded. The diagram also includes a configuration snippet that defines VLAN and ring configuration for the master role.