Configuring Circular Route Detection

Note:

Circular route detection is not supported in ITU networks.

This procedure is used to configure the EAGLE to detect circular routing with the chg-stpopts command. The chg-stpopts command uses these parameters to detect circular routing in the EAGLE.

:on=mtplti - to turn on the circular routing detection feature.

:off=mtplti - to turn off the circular routing detection feature.

:mtpltctdpcq – the number of DPCs that the circular route test message is sent to.

:mtpltst – the duration of the circular route test detection procedures, in milliseconds (the MTPLTST timer).

These parameters are optional. For any parameters not specified with the chg-stpopts command, the values for these parameters are not changed.

When the on=mtplti parameter is specified for the chg-stpopts command, the value yes is shown in the MTPLTI field of the rtrv-stpopts output. When the off=mtplti parameter is specified for the chg-stpopts command, the value no is shown in the MTPLTI field of the rtrv-stpopts output.

The system default values, shown in the rtrv-stpopts output, for these parameters are:

MTPLTI - yes
MTPLTCTDPCQ - 3
MTPLTST - 10000.

For this example, the circular route detection procedures remain enabled, the number of most frequently occurring DPCs is changed from 3 to 6, and the duration of the circular route detection procedures is changed from 10000 milliseconds to 18000 milliseconds.

The EAGLE automatically tests for circular routing when congestion occurs on an ANSI signaling link. The circular route detection test cannot be performed for ITU signaling links. If the routing data is configured incorrectly, or is corrupted, MSUs could be routed in an endless circular route. The incorrect routing data could be on the EAGLE or at a remote node. With the addition of cluster routing and E links, the danger of circular routing is greater.

The EAGLE starts the test when a signaling link reaches onset congestion threshold 1. The EAGLE only runs the test for one signaling link per linkset. If a second signaling link in the same linkset goes into congestion, the EAGLE does not start a new test. Each time the signaling link’s congestion level increases, the test is restarted. The LIM that contains the congested signaling link determines which DPCs have the most MSUs transmitted on the signaling link. The LIM then transmits a circular routing test message to the DPCs that have sent the most MSUs. The number of DPCs that the circular route test message is sent to is from 3 to 10. A circular routing test message is a routeset congestion test message with priority of 3.

If any LIM receives one of the test messages before the MTPLTST timer expires, the EAGLE performs these actions.

Marks the destination as prohibited due to circular routing.
Broadcasts TFPs for the destination.
Reports that circular routing was detected for the destination.
Raises a critical alarm.

The destination remains prohibited until it is manually allowed using the rst-dstn (reset destination) command.

If the destination is a cluster point code entry in the routing table, then an exception list (x-list) entry is created for the destination. If the cluster has the exception list exclusion indicator set to yes (meaning do not create x-lists for that cluster), then an x-list is not created, an UAM is generated, and a critical alarm is raised for the cluster. The critical alarm can be cleared by entering the rst-dstn command for the cluster.

If an x-list entry needs to be created, but the provisioned number of x-lists are already used, extra buffer space, equal to 100 entries in the routing table, is used to create the x-list. If this extra buffer space is also full, no x-list is created, a UAM is generated, and a critical alarm is raised for the cluster.

When a point code is prohibited due to circular routing, the EAGLE ignores TFx/TCx management messages for that point code. The EAGLE does not send routeset test messages for the point code. The EAGLE discards any MSUs received for the point code and sends response method TFPs or TCPs.

When EAGLE detects circular routing for a destination, it sets the circular routing flag for the destination in the routing table. The rst-dstn command clears this flag. Once the circular routing flag is cleared, the status of the destination depends on what type of entry is used.

If the destination is a member of a cluster for which EAGLE performs full point code routing only, all routes to the destination are marked as allowed and the destination’s status is allowed. The EAGLE broadcasts TFAs for the destination.
If the destination has a full point code entry in the routing table, and there is also an entry for the point code’s cluster, then each route used by the point code that is also used by the cluster entry assumes the status of the route for the cluster entry. Each route used by the point code that is not used by the cluster assumes the status of the cluster’s route set. The EAGLE then determines the point codes route set status and broadcasts TFA/TFR if the point code becomes allowed or restricted.

If the rst-dstn command is entered for an x-list entry with the circular routing flag set, the x-list entry is deleted. The point code’s status becomes the same as the cluster entry’s status.

If Circular Route Auto-Recovery is enabled and turned on, and circular routing because of far-end loopback is detected, the status of the destination marked as prohibited is automatically cleared. Refer to the Activating the Circular Route Auto-Recovery Feature procedure for more information.

Display the existing values for the circular route test parameters by entering the rtrv-stpopts command.
The value for the circular route test parameters is shown in the MTPLTI, MTPLTCTDPCQ, MTPLTST fields. This is an example of the possible output.
```
rlghncxa03w 06-10-17 16:02:05 GMT  EAGLE5 36.0.0
STP OPTIONS
-----------------------
MTPLTI              no
MTPLTCTDPCQ          3
MTPLTST          10000
```
Note:
The rtrv-stpopts command output contains other fields that are not used by this procedure. If you wish to see all the fields displayed by the rtrv-stpopts command, see the rtrv-stpopts command description in Commands User's Guide.
Change the circular routing detection parameters by entering the chg-stpopts command with at least one of these parameters..
- on=mtplti - if the current MTPLTI value is no.
- off=mtplti - if the current MTPLTI value is yes.
- mtpltctdpcq
- mtpltst
For this example, enter this command.

chg-stpopts:mtpltctdpcq=6:mtpltst=18000:on=mtplti

When this command has successfully completed, this message should appear.
```
rlghncxa03w 06-10-07 00:22:57 GMT  EAGLE5 36.0.0
CHG-STPOPTS: MASP A - COMPLTD
```
Verify the changes using the rtrv-stpopts command.
This is an example of the possible output.
```
rlghncxa03w 06-10-17 16:02:05 GMT  EAGLE5 36.0.0
STP OPTIONS
-----------------------
MTPLTI             yes
MTPLTCTDPCQ          6
MTPLTST          18000
```
Note:
The rtrv-stpopts command output contains other fields that are not used by this procedure. If you wish to see all the fields displayed by the rtrv-stpopts command, see the rtrv-stpopts command description in Commands User's Guide.

Back up the new changes using the chg-db:action=backup:dest=fixed command.

These messages should appear, the active Maintenance and Administration Subsystem Processor (MASP) appears first.

BACKUP (FIXED) : MASP A - Backup starts on active MASP.
BACKUP (FIXED) : MASP A - Backup on active MASP to fixed disk complete.
BACKUP (FIXED) : MASP A - Backup starts on standby MASP.
BACKUP (FIXED) : MASP A - Backup on standby MASP to fixed disk complete.

Figure 3-26 Configuring Circular Route Detection