MC ring groups overview
Overview
MC ring groups are an extension of dual-homing support that provides aggregation redundancy in networks that have multiple access nodes, called ring nodes in the context of MC ring groups, that are connected in a single ring.
The 7210 SAS, 7450 ESS, 7750 SR, and 7950 XRS support the creation of MC ring groups using Ethernet ports in Access mode.
Support for MC ring groups on the 7210 SAS varies depending on the chassis type and release; see the NE documentation for support information.
The following figure shows a simple subscriber aggregation network in which a single ring of access nodes, such as DSLAMs, is connected to a BSA in a VPLS. Each BSA is connected to an IES or VPRN L3 interface on a BSR using a spoke SDP. Each BSR L3 interface aggregates the subscriber traffic in one subnet.
Figure 45-1: Simple subscriber aggregation network
Note: BTV distribution is typically implemented in a separate VPLS that uses one SAP per access node.
An MC ring group does not support a ring that has more than one break.
Steady-state condition
In an MC ring group, the operation of a typical dual-homed ring is as shown in Figure 45-2, Dual-homed ring, steady-state condition . A steady-state condition is defined by the following.
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The participating BSAs have matching MC ring configurations.
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The In-Band Ring Control Connection, or IB-RCC, is operationally up.
Figure 45-2: Dual-homed ring, steady-state condition
The IB-RCC is set up using a BFD session between IES or VPRN IP interfaces on BSA 1 and BSA 2. This connection requires a separate ring VLAN.
You can create an MC ring group only in an MC peer group. When only one peer in an MC peer group is managed by the NFM-P, you can configure node redundancy parameters only for the managed peer and only from the NE properties form. See Chapter 40, MC peer groups for information about MC peer groups.
In the steady state, the ring is fully closed and each ring node has two paths to the VPLS core; the paths are shown in as Path A and Path B in Figure 45-2, Dual-homed ring, steady-state condition . To prevent a communication loop, a ring node can use only one path for VLAN traffic. The VLAN range can be explicitly assigned to Path B on each BSA; by default, the SAP uses Path A. The VLAN range assignment for each path must be the same on each BSA. A SAP in the conflict range is assigned to Path A, regardless of the local configuration.
Each SAP in the path that ends on the master BSA is operationally up. Each subscriber-host forwarding database entry associated with the SAP points to the SAP. Each SAP in the path that ends on the standby BSA is operationally down. Each subscriber-host forwarding database entry associated with the SAP points to the mesh SDP that connects to the master BSA.
The master BSA periodically performs a Ring Node Connectivity Verification, or RNCV, check. The loss of connectivity to a ring node does not automatically trigger a switchover to the other path; if the IB-RCC BFD session is up, the ring is considered closed, and the master and standby BSA roles do not change.
Broken ring condition
A broken ring condition occurs when there is a link failure or ring node failure, as shown in the following figure. In this condition, the IB-RCC is operationally down. Each ring node has only one path to the VPLS core.
Figure 45-3: Dual-homed ring, broken-ring condition
Each BSA becomes the master for the ring nodes that it can reach, and performs as described in the steady-state condition. Each L2 SAP on each BSA is operationally up, except the SAPs that are explicitly excluded from the MC ring control.
In the broken-ring condition, each BSA performs an RNCV check because each is a master. The forwarding database entry for each subscriber host behind an unreachable ring node points to the mesh SDP.
When the MC ring connectivity is restored, one BSA is the master for Path A and the other BSA is the master for Path B.
Object relationships
The following figure shows the MC ring and ring node object relationships with equipment and service objects.
Figure 45-4: MC ring group object relationships
An MC ring has a one-to-one relationship with an MC synchronization tag. An MC ring uses one IES or VPRN service for IB-RCC. An MC ring can have multiple ring nodes, and each ring node can use only one SAP for RNCV.
When an MC ring group is correctly configured, each BSA L2 SAP is protected by the ring. The service that contains these protected SAPs is referred to as the user service. The service that is used for RNCV is an MVPLS that can also contain user SAPs and be a user service.
MC ring group and redundant VLL Epipe access
An MC ring group can connect to a VLL SAP to support redundant VLL Epipe access. The following figure shows a sample configuration using a VLL Epipe.
Figure 45-5: Dual-homed VLL Epipe configuration
CPE 1 connects to a ring node that has access to each BSA through a VLAN that is provisioned on each ring node. The SAP on each BSA uses the same VLAN tag.
In the closed ring on the left, BSA 1 is the master and sends an active status notification to BSA 3 on a VLL Epipe. BSA 2, the standby, sends a standby status notification. Based on this information, BSA 3 chooses a path to reach CPE 2.
In the broken ring on the right, the BSA that can use RNCV to reach CPE 1 becomes the master and sends an active status notification to BSA 3 on a VLL Epipe.
In each scenario, only one SAP is operationally up at a time, and each Epipe must be operationally up. If the ring node of CPE 1 is operationally down, neither BSA can reach the ring node, so each SAP and Epipe is operationally down.
MC ring groups and subscriber hosts
Each subscriber host on a SAP that is protected by an MC ring group must be associated with a ring node to determine whether the subscriber host is reachable by the BSA. Each VLL Epipe used for forwarding from an MC ring group must be explicitly configured with the name of a ring node in the MC ring. See To configure an MC ring group for redundant VLL Epipe access for information about configuring VLL Epipes for use with an MC ring group.
When subscriber management is enabled on a VPLS SAP, each dynamic subscriber host is automatically associated with a ring node. Static hosts on a VPLS SAP require explicit configuration. The following must be true before you can turn up an MC ring on a VPLS SAP that has one or more static hosts, or turn up a static host o. a VPLS SAP in an operational MC ring: