Specifications

232 ExtremeWare XOS 11.0 Concepts Guide
Extreme Standby Router Protocol
standard mode if your network contains both switches running ExtremeWare and switches running
ExtremeWare XOS participating in ESRP.
Extended mode supports and is compatible with switches running ExtremeWare XOS while
participating in ESRP. Use extended mode if your network contains only switches running ExtremeWare
XOS.
The following list describes the major differences in behavior between standard and extended 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. Handshaking 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.
• 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 configure esrp <esrpDomain> domain-id <number>
command
— 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.