Avaya 8800 Planning And Engineering, Network Design page 81

provides redundant default gateway configurations, additionally has BackupMaster capability.
BackupMaster improves the Layer 3 capabilities of VRRP operating in conjunction with SMLT.
Avaya recommends that you use a VRRP BackupMaster configuration with any SMLT configuration
that has an existing VRRP configuration.
A better alternative than SMLT with VRRP BackupMaster is to use RSMLT L2 Edge. For Release
5.0 and later, Avaya recommends that you use RSMLT L2 Edge configuration, rather than SMLT
with VRRP BackupMaster, for those products that support RSMLT L2 Edge. RSMLT L2 Edge
provides:
• Greater scalability—VRRP scales to 255 instances, while RSMLT scales to the maximum
number of VLANs.
• Simpler configuration—Simply enable RSMLT on a VLAN; VRRP requires virtual IP
configuration, along with other parameters.
For connections in pure Layer 3 configurations (using a static or dynamic routing protocol), a Layer
3 RSMLT configuration is recommended over SMLT with VRRP. In these instances, an RSMLT
configuration provides faster failover than one with VRRP because the connection is a Layer 3
connection, not just a Layer 2 connection for default gateway redundancy.
Important:
In an SMLT-VRRP environment that has VRRP critical IP configured within both IST core
switches, routing between directly connected subnets ceases to work when connections from
each of the switches to the exit router (the critical IP) fail. Avaya recommends that you do not
configure VRRP critical IPs within SMLT or R-SMLT environments because SMLT operation
automatically provides the same level of redundancy.
As well, do not use VRRP BackupMaster and critical IP at the same time. Use one or the other.
Do not use VRRP in RSMLT environments.
Typically, only the VRRP Master forwards traffic for a given subnet. If you use BackupMaster on the
SMLT aggregation switch, and it has a destination routing table entry, then the Backup VRRP switch
also routes traffic. The VRRP BackupMaster uses the VRRP standardized backup switch state
machine. Thus, VRRP BackupMaster is compatible with standard VRRP. This capability is provided
to prevent the traffic from edge switches from unnecessarily utilizing the IST to deliver frames
destined for a default gateway. In a traditional VRRP implementation, this operates only on one of
the aggregation switches.
The BackupMaster switch routes all traffic received on the BackupMaster IP interface according to
the switch routing table. The BackupMaster switch does not Layer 2-switch the traffic to the VRRP
Master.
You must ensure that both SMLT aggregation switches can reach the same destinations by using a
routing protocol. Therefore, Avaya recommends that, for routing purposes, you configure per-VLAN
IP addresses on both SMLT aggregation switches. Avaya further recommends that you introduce an
additional subnet on the IST that has a shortest-route-path to avoid issuing Internet Control
Message Protocol (ICMP) redirect messages on the VRRP subnets. (To reach the destination,
ICMP redirect messages are issued if the router sends a packet back out through the same subnet
on which it is received.)
June 2016 Planning and Engineering — Network Design
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Network redundancy
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