ESRP Extended Mode Features

The ESRP extended mode is enabled by default and provides the maximum ESRP feature set.

You can use ESRP extended mode only when all switches that participate in ESRP are running ExtremeXOS software.

The following list describes the ESRP extended mode features that are not available in standard mode:

• Handshaking

  In standard mode, events such as link flapping cause the ESRP master switch to generate a large number of packets and to increase processing time.

  To prevent this, extended mode supports handshaking, which occurs when a switch requests a state change, forces its neighbor to acknowledge the change, and the neighbor sends an acknowledgement to the requesting switch. For example, if a slave switch wants to become the master, it enters the pre-master state, notifies the neighbor switch, and forces the neighbor to acknowledge the change. The neighbor then sends an acknowledgement back to the slave switch. While the requesting switch waits for the acknowledgements, future updates are suppressed to make sure the neighbor does not act on incorrect data.

• Stickiness

  In standard mode, if an event causes the ESRP master switch to fail over to the slave, it becomes the new master. If another event occurs, the new master switch returns to the slave and you have experienced two network interruptions.

  To prevent this, extended mode supports the sticky election metric. The default election algorithm uses the sticky metric. For example, if an event causes the ESRP master switch to fail over to the slave, it becomes the new master and has a higher sticky value. If another event occurs, for example adding active ports to the slave, the new master does not fail back to the original master even if the slave has more active ports. After sticky is set on the master, regardless of changes to its neighbor‘s election algorithm, the new master retains its position. Sticky algorithms provide for fewer network interruptions than non-sticky algorithms. Sticky is set only on the master switch.

• Port weight

  In standard mode, the port count calculation does not take into account the available bandwidth of the ports. For example, a switch with a one Gigabit Ethernet uplink may be unable to become master because another switch has a load-shared group of four fast Ethernet links. The active port count calculation considers only the number of active ports, not the bandwidth of those ports.

  In extended mode, the active port count calculation considers the number of active ports and the port weight configuration considers the bandwidth of those ports. You enable port weight only on the load-shared master port.

• Domain ID

  In standard mode, ESRP packets do not contain domain information; therefore, the only information about the packet comes from the receiving port.

  The concept of domain ID is applicable only to extended mode. A domain ID in the packet clearly classifies the packet, associates a received ESRP PDU to a specific ESRP domain, and tells the receiving port where the packet came from. In extended mode, you must have a domain ID for each ESRP domain. Each switch participating in ESRP for a particular domain must have the same domain ID configured.

  The ESRP domain ID is determined from one of the following user-configured parameters:

• ESRP domain number created with the command:

  configure esrp esrpDomain domain-id number

• 802.1Q tag (VLANid) of the tagged master VLAN

• Hello messages

  In standard mode, both the master switch and slave switch send periodic ESRP hello messages. This causes an increase in packet processing by both the master and slave.

  In extended mode, the master switch sends periodic ESRP hello messages. This reduces the amount of packet processing, increases the amount of available link bandwidth, and does not impact communicating state changes between switches.

• ESRP Automatic Toggle Feature

  ESRP includes an automatic toggle feature, which toggles to the same mode of operation as an ESRP neighbor. This action causes the switch to enter the neutral state and re-elect the ESRP master.

  

  Note

  The automatic toggle feature toggles the ESRP operational mode, not the configured mode. If the switch is configured for ESRP extended mode and the switch toggles to standard mode, the switch enters extended mode the next time the switch boots.