Nested Cluster Routing

When a node is switching traffic to remote (non-adjacent) nodes, it is possible that an STP is using at least one route that is different from the other members of a cluster. Typically, this occurs when the node is directly connected to the member of a cluster, such as when an STP has A-links or E-links that are connected to a member. The nested cluster routing feature provides a mechanism that allows both cluster and member routes to be provisioned in the same cluster.

Nested Clusters and Cluster Members

The cluster routing and management feature requires that routes to a cluster and members of that cluster be in the same routeset. With the nested cluster routing feature, however, users can have certain members of the provisioned cluster with different full point code routesets. This different routeset may be totally different, partially different, or exactly the same.

With the nested cluster routing feature, routes to these members can be changed, deleted, or added. Deletion of a full point code route entry within a cluster will result in the member using the cluster entry for routing. Deletion of a cluster route entry will not delete the full point code route entry. This holds true even if the full point code entry and the cluster have the same route.

The EAGLE sends cluster network management messages (TCA, TCR, TCP) based on the least restrictive of the cluster's routeset status, and the routeset status of any full point code entries within the cluster.

The nested cluster routing feature provides a new routing model. The EAGLE allows several routing models. Table 2-9 describes coupling between the cluster and its members. Coupling describes the relationship between the cluster and member routes.

Table 2-9 Routing Models

System Routing Model	Characteristics	Issues and Resolution
Full Point Code Routing (FPR) No coupling	The EAGLE behaves as a full point code router when the Cluster Routing and Management Diversity feature is off. Only full point code destinations are provisioned. The EAGLE never generates TCx messages concerning clusters of provisioned members. Received TCx messages are applied to all members of the concerned cluster.	No issues. There is no coupling between cluster status and member statuses due to the lack of clusters.
Cluster Routing (CR) No coupling NCAI=No	With the Cluster Routing and Management Diversity feature on, the EAGLE allows the provisioning of cluster destinations. For cluster destinations, only cluster destinations are provisioned. The EAGLE generates TCx messages only for provisioned cluster destinations. All received TCx messages are applied to concerned cluster entry, if it exists. Otherwise, it is applied to all individual members.	No issues. There is no coupling between cluster status and member status due to the lack of members belonging to provisioned cluster.
Cluster Routing and Management Diversity (CRMD) Full coupling NCAI=No	In this mode, the EAGLE allows provisioning of clusters as well as members of same clusters. Here cluster and member have the same routeset, and they are fully coupled. All TCx messages are applied to members, and TCx messages generated by the EAGLE reflect member status. In this mode, the member status cannot be less restrictive than the cluster.	No issues regarding network management message generation and processing. Cluster and members cannot have a different routeset, and thus E-links cannot be provisioned for members of a cluster.
Nested Cluster Routing No coupling NCAI=Yes	In this mode, if the ncai parameter is yes (provided both the nested cluster routing and the Cluster Routing and Management Diversity features are on), the user can enter a cluster routeset, then enter a different routeset for a member of that cluster. In this case, member routeset status can be less restricted than cluster routeset status.	There is an issue regarding broadcasting network management messages. Because members can be less restricted than the cluster, the broadcast of cluster messages (TCA, TCR, TCP) is based on the least restrictive of the following: The cluster’s routeset status. The routeset status of any full point code entries within the cluster. Also, when the ncai parameter is yes, the EAGLE does not generate preventive TCP messages.

Administration

The nested cluster routing feature is provisioned using the ncai parameter of either the ent-dstn or chg-dstn commands. The ncai parameter can only be specified for cluster point codes.

In order to specify the ncai parameter, both the Cluster Routing and Management Diversity and the nested cluster routing features must be on. If the ncai parameter is yes, the EAGLE allows certain members of the provisioned cluster to have a different full point code routeset.

If the ncai parameter is no, standard command-handler rules apply (any full point code routeset within a cluster must have the same routeset as the cluster). If ncai parameter is yes, new command-handler rules apply (full point code routeset can be different from the cluster routeset). Figure 2-24 provides an example of provisioning a nested cluster and its associated members.

Nested Cluster Routing Rules of Operations

The following rules apply to nested clusters (cluster entries with the ncai parameter set to yes):

1. The EAGLE allows the user to enter a full point code routeset entry even if the point code is a member of a cluster that has a different routeset. For example, in Figure 2-24, the provisioned member 5-5-1 has a different routeset than the cluster's routeset.
2. When the EAGLE broadcasts network management messages relating to the cluster, the EAGLE uses the least restricted of the following to determine which cluster message (TCA, TCR, TCP) to send:
   • The cluster's routeset status
   • The routeset status of any full point code entries within the cluster

     For example, in Figure 2-24, if linkset LSB fails, a TCP message for cluster 5-5-* is not broadcast because the least restrictive status of provisioned member 5-5-1 is allowed.

3. The EAGLE does not send preventive TCPs when it begins routing toward a nested cluster. The EAGLE sends response-method preventive TFPs if it receives an MSU and there is danger of circular routing. For example, in Figure 2-24, the EAGLE does not send a preventive TCP for cluster 5-5-* when routing to cluster 5-5-* over linkset LSB. However, if the EAGLE receives an MSU on linkset LSB destined for node 5-5-2, the EAGLE discards the MSU and sends a TFP to node B concerning node 5-5-2.

   Note:

   The EAGLE will still send preventive TFPs when it starts routing toward a full point code member of a nested cluster.
4. The EAGLE replies to RCx cluster routeset test messages, using the less restrictive routeset status as indicated in rule #2.
5. The EAGLE replies to RSx full point code routeset messages, using the full point code's routeset status and the danger of circular routing.
6. Response method TFP or TFR is used when the cluster destination is more restrictive than a full point code member. The modified TFP response method will send no more than one TFP per cluster member during the time period defined by the level 3 T8 timer. The modified TFR response method sends no more than one response TFR per cluster member.

Nested Cluster Routing Example

Figure 2-24 provide an example of nested cluster routing. Table 2-10 and Table 2-11 show the routing tables for the cluster point code and one of the members of the cluster point code. Table 2-12 shows what actions the EAGLE takes when the linksets in a nested cluster configuration fail and recover. The actions in Table 2-12 are based on the example nested cluster routing configuration shown in Figure 2-24.

Figure 2-24 Nested Cluster Routing Sample Configuration

Table 2-10 Routing Table for Nested Cluster 5-5-*

Linkset Name	Route DPC	Cost Value of the Route
LSB	5-5-*	10
LSC	5-5-*	20

Table 2-11 Routing Table for Full Point Code Member 5-5-1

Linkset Name	Route DPC	Cost Value of the Route
LSE	5-5-1	5
LSB	5-5-1	10
LSC	5-5-1	20

Table 2-12 Example of Nested Cluster Routing Failure and Recovery Actions

Event	Action
All linksets are up and all routes are available.	The EAGLE does not send a preventive TCP for cluster 5-5-* to node B because cluster 5-5-* is a nested cluster. Messages are routed to SSP 5-5-1 using linkset LSE and to cluster 5-5-* using linkset LSB. The EAGLE broadcasts TCAs concerning cluster 5-5-* to nodes SSP1, SSP 5-5-1, node A, and node B.
The linkset between node B and SSP 5-5-2 fails. Node B sends a TFP concerning SSP 5-5-2.	The EAGLE creates an x-list entry for point code 5-5-2 and marks it prohibited on linkset LSB. The EAGLE broadcasts TFPs to SSP1, SSP 5-5-1 and node A and sends response method TFP concerning point code 5-5-2. The EAGLE starts an RSP for SSP 5-5-2 on linkset LSB.
The linkset between node B and SSP 5-5-1 fails. Node B sends a TFP for SSP 5-5-1 to the EAGLE.	The EAGLE marks full point code 5-5-1 as prohibited on linkset LSB. The EAGLE routes the traffic to SSP 5-5-1 using linkset LSE. The EAGLE starts an RSP for SSP 5-5-1 on linkset LSB.
The linkset between node B and SSP 5-5-2 recovers, and node B sends a TFA for SSP 5-5-2 to the EAGLE.	The EAGLE removes point code 5-5-2 from the exception list. The status of linkset LSB is changed from prohibited to allowed. Traffic is routed to SSP 5-5-2 using linkset LSB. The EAGLE broadcasts a TFA concerning SSP 5-5-2 to SSP1, SSP 5-5-1 and node A. The EAGLE sends a preventive TFP concerning SSP 5-5-2 to node B.
The linkset between node B and SSP 5-5-1 recovers, and node B sends a TFA concerning SSP 5-5-1 to the EAGLE.	The EAGLE marks full point code 5-5-1 as allowed on linkset LSB.
Linkset LSB fails.	The EAGLE stops using linkset LSB to send traffic to cluster 5-5-*. Linkset LSB is marked prohibited, forced rerouting is performed, level 3 timer T11 for cluster 5-5-* is started, and starts using linkset LSC to send traffic to cluster 5-5-*. The EAGLE marks cluster 5-5-* restricted on linkset LSC for all members of cluster 5-5-* except full point code 5-5-1. When level 3 timer T11 expires, a TFR response method is sent for all members of cluster 5-5-* except full point code 5-5-1.
SSP1 sends an MSU with DPC=5-5-2.	The EAGLE responds with TFR concerning SSP 5-5-2 to SSP1. The MSU is routed on linkset LSC.
SSP1 sends an MSU with DPC=5-5-1.	The EAGLE routes the MSU to SSP 5-5-1 using linkset LSE.
Linkset LSB recovers.	The EAGLE stops using linkset LSC to send traffic to cluster 5-5-*, performs controlling rerouting on cluster 5-5-*, marks cluster 5-5-* as allowed on linkset LSB, and starts routing traffic to cluster 5-5-* using linkset LSB.
The SSP sends a routeset test (RSR) concerning SSP 5-5-2 to the EAGLE.	The EAGLE responds with a TFA concerning SSP 5-5-2.
Linkset LSC fails.	The EAGLE stops using linkset LSC to send traffic to cluster 5-5-* or full point code 5-5-1, and marks cluster 5-5-* and full point code 5-5-1 as prohibited on linkset LSC.
Linkset LSC recovers.	The EAGLE marks cluster 5-5-* and full point code 5-5-1 as allowed on linkset LSC.
Linkset LSE fails.	The EAGLE stops using linkset LSE to send traffic to SSP-5-5-1, marks SSP 5-5-1 as prohibited on linkset LSE, performs forced rerouting, starts level 3 timer T11 concerning SSP 5-5-1, sends preventive TFP concerning SSP 5-5-1 to node B, and starts using linkset LSB to send traffic to full point code 5-5-1. The EAGLE marks full point code 5-5-1 as restricted on linkset LSB. When level 3 timer T11 expires, a TFR concerning SSP 5-5-1 is sent to SSP1 and node A.
SSP1 sends an MSU with the DPC 5-5-2.	The EAGLE routes the MSU to SSP 5-5-2 using linkset LSB.
SSP1 sends an MSU with the DPC 5-5-1.	The EAGLE responds with a TFR concerning SSP 5-5-1 to SSP1. The MSU is routed to SSP 5-5-1 using linkset LSB.
Linkset LSE recovers.	The EAGLE stops using linkset LSB to send traffic to SSP 5-5-1, performs controlling rerouting on full point code 5-5-1, marks full point code 5-5-1 as allowed on linkset LSE, and starts routing traffic to full point code 5-5-1 using linkset LSE. The EAGLE broadcasts a TFA for SSP 5-5-1 to SSP1, node A, and node B.

Limitations of the Nested Cluster Routing Feature

The EAGLE only supports a maximum of 200 nested cluster destinations. This limit does not apply to non-nested clusters (clusters with the ncai parameter set to no).

If a cluster is more restricted than a member, the EAGLE broadcasts the status of the least restricted member, and relies on response method for members of the cluster that do not have a full point code entry.

The EAGLE does not broadcast preventive TCPs for nested cluster destinations. Because the EAGLE does not send preventive TCPs when it begins routing toward a nested cluster, circular routing can occur. The EAGLE sends response method TFPs if it receives an MSU when there is a danger of circular routing.