Specifications

ESRP Concepts
ExtremeWare XOS 11.0 Concepts Guide 233
ESRP Domains
ESRP domains allow you to configure multiple VLANs under the control of a single instance of the
ESRP protocol. By grouping multiple VLANs under one ESRP domain, the ESRP protocol can scale to
provide protection to large numbers of VLANs. All VLANs within an ESRP domain simultaneously
share the same active and standby router and failover router, as long as one port of each member VLAN
belongs to the domain master.
Depending on the election policy used, when a port in a member VLAN belongs to the domain master,
the member VLAN ports are considered when determining the ESRP master. You can configure a
maximum of 64 ESRP domains in a network.
If you disable an ESRP domain, the switch notifies its neighbor that the ESRP domain is going down,
and the neighbor clears its neighbor table. If the master switch receives this information, it enters the
neutral state to prevent a network loop. If the slave switch receives this information, it enters the
neutral state.
ESRP Domain IDs
ESRP packets do not identify themselves to which domain they belong; you either configure a domain
ID or the ESRP domain uses the 802.1Q tag (VLANid) of the master VLAN. 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.
Linking ESRP Switches
When considering system design using ESRP, Extreme Networks recommends using a direct link. Direct
links between ESRP switches are useful under the following conditions:
• A direct link can provide a more direct routed path, if the ESRP switches are routing and supporting
multiple VLANs where the master/slave configuration is split such that one switch is master for
some VLANs and a second switch is master for other VLANs. The direct link can contain a unique
router-to-router VLAN/subnet, so that the most direct routed path between two VLANs with
different master switches uses a direct link, instead of forwarding traffic through another set of
connected routers.
• A direct link can be used as a highly reliable method to exchange ESRP hello messages, so that the
possibility of having multiple masters for the same VLAN is lessened if all downstream Layer 2
switches fail.
• A direct link is necessary for the ESRP host attach (HA) option. The direct link is used to provide
Layer 2 forwarding services through an ESRP slave switch.
Direct links may contain a router-to-router VLAN, along with other VLANs participating in an ESRP
domain. If multiple VLANs are used on the direct links, use 802.1Q tagging. The direct links may be
aggregated into a load-shared group, if desired. If multiple ESRP domains share a host port, each VLAN
must be in a different ESRP group.
ESRP and Hitless Failover
ExtremeWare XOS 11.0 introduces support of hitless failover. When you install two Management Switch
Fabric Module (MSM) modules in a BlackDiamond chassis, one MSM assumes the role of primary and
the other assumes the role of backup MSM. The primary MSM executes the switch’s management
functions, and the backup MSM acts in a standby role. Hitless failover transfers switch management