Smlt Overview - Avaya 8600 Configuration Manual

Link aggregation fundamentals
• MLT-based SMLT with Single Port SMLT
• SMLT and LACP support
• SMLT and IP routing
• SMLT and SLPP

SMLT overview

Split MultiLink Trunking (SMLT) is an option that improves Layer 2 (bridged) resiliency by
providing for the addition of switch failure redundancy with sub-second failover, on top of all
standard MLT link failure protection and flexible bandwidth scaling functionality. SMLT allows
you to connect any device which supports some form of link aggregation, be it a switch or a
server, to two distinct separate SMLT endpoints or switches. These SMLT switches form a
Switch Cluster and are referred to as an IST Core Switch pair.
Switch Clusters are always formed as a pair, but pairs of clusters can be combined in either a
square of full-mesh fashion to increase the size and port density of the Switch Cluster. When
configured in a Layer 3 or routed topology, the configuration is referenced as Routed SMLT
(RSMLT). For information about Routed SMLT, see Avaya Ethernet Routing Switch 8800/8600
Configuration — IP Routing (NN46205-523).
Important:
In the case of a full-mesh SMLT configuration between 2 Clusters running OSPF (more likely
an RSMLT configuration) because of the way that MLTs work in regards to CP-generated
traffic, Avaya highly recommends that the MLT port (or ports) that form the square leg of the
mesh (versus the cross connect) be placed on lowered number slot/port than the cross
connections. The reason for this is because CP-generated traffic is always sent out on the
lowered numbered ports when active. Using this recommendation will keep some OSPF
adjacency up if all the links of the IST fail. Otherwise the switches which have a failed IST
could lose complete OSPF adjacency to both switches in the other Cluster and therefore
become isolated.
SMLT connections can be formed via single links from the switch cluster to the edge
connection, Single Link SMLT (SLT), or via standard MLTs, or MLTs with LACP. Optionally,
SMLT links can have VLACP enabled as well. These various link connections can be mixed.
Within the same Switch Cluster, both SMLT and RSMLT can be configured, allowing a mixture
of both Layer 2 and Layer 3 VLANs. For examples of various SMLT configurations, refer to
SMLT topologies
Important:
In SLT configurations where the SLT port and all the IST_MLT ports are configured on the
same physical module (not a best practice design; IST_MLT should always be a D-MLT),
the switch can experience FDB entry learning issues for MAC addresses learned across the
IST. This can lead to connectivity loss. This condition can occur if the module is physically
swapped out during switch operation, or if the module is disabled/enabled via CLI or EDM.
The switch relearns the FDB entries after the fdb-ageout time, or you can manually
relearn them by performing an fdb-entry flush on the relevant VLANs.
SMLT networks do not need to use the IEEE 802.1d STP to enable loop-free triangle topologies
because SMLT inherently avoids loops due to its superior enhanced link aggregation protocol.
24 Configuration — Link Aggregation, MLT, and SMLT
on page 37
on page 38
on page 39
on page 26.
Comments? infodev@avaya.com
on page 35
January 2012