To provide the fault tolerance shown in the following figure through the following figure, the redundant network nodes communicate with each other to determine the active primary and inactive secondary status and elect an active master node.
For a VPLS domain type, ESRP (Extreme Standby Router Protocol) considers election factors in the following order: standby, active ports, tracking information, stickiness, ESRP priority, and MAC. For more information on the ESRP election priority, see ESRP.
For fault tolerant VPLS to function correctly, the ExtremeXOS software imposes restrictions on the configuration options on the VPLS redundancy type ESRP domain. ESRP Configuration Restrictions for VPLS Type Domains lists the configuration restrictions on the control VLAN (Virtual LAN).
ESRP Configuration Restrictions for VPLS Type Domains
| No. | Parameter | Restrictions | Remarks |
|---|---|---|---|
| 1 | mode | Not configurable | Only extended mode is supported. |
| 2 | elrp poll | Always enabled on control VLAN ports | Enabled because control VLANs can have loops. That is, a control VLAN is protecting an S-VLAN in an EAPS (Extreme Automatic Protection Switching) ring. |
| 3 | master VLAN | No restrictions | The ESRP control VLAN is configured as the master VLAN on the ESRP master and slave. |
| 4 | member VLAN | Not configurable | Member VLANs are not configured for the domain since we would need the slave node to perform L2 switching and L3 forwarding. |
| 5 | track-environment | Not configurable | Tracking is always done on pseudowires. |
| 6 | track-VLAN | Not configurable | Tracking is always done on pseudowires. |
| 7 | track-IProute | Not configurable | Tracking is always done on pseudowires. |
| 8 | track-Ping | Not configurable | Tracking is always done on pseudowires. |
| 9 | domain-id | None | |
| 10 | elrp-master-poll | No restrictions | Not configurable, disabled by default. |
| 11 | elrp-premaster-poll | No restrictions | Not configurable, disabled by default. |
| 12 | election policy | Not configurable | Always set to: standby > ports > track > sticky > priority > mac. |
| 13 | name | No restrictions | |
| 14 | priority | No restrictions | |
| 15 | timer | No restrictions | When the service VLAN is part of an EAPS ring, it is strongly recommended that the hello timer is always greater than the EAPS master health checkup timer because an ESRP switch before EAPS could cause traffic loops. |
The MTU nodes in the following figure signal the PE nodes about active/inactive state using the Status TLV defined in RFC 4447, Pseudowire Setup and Maintenance Using the Label Distribution Protocol (LDP). This operation is described in Redundant Spoke Pseudowire Connections.
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