Avaya 8800 Planning And Engineering, Network Design page 80

Redundant network design
Single Link Trunking (SLT)
Use Single Link Trunking (SLT) to configure a split multilink trunk that uses a single port. A single-
port split multilink trunk behaves like an MLT-based split multilink trunk and can coexist with split
multilink trunks in the same system. However, on each chassis, an SMLT ID can belong to either an
MLT-SMLT or to an SLT. Use SLT to scale the number of split multilink trunks on a switch to the
maximum number of available ports.
On the SMLT aggregation switch pair, split multilink trunks can exist in the following combinations:
• MLT-based split multilink trunks and MLT-based split multilink trunks
• MLT-based split multilink trunks and SLTs
• SLTs and SLTs
SLT configuration rules include:
• The dual-homed device that connects the aggregation switches must support MLT.
• SLT is supported on Ethernet, and POS ports.
• Assign SMLT IDs of 129 to 512 to SLTs and reserve the lower number IDs of 1 to 128 for
SMLT only.
• SLT ports can be designated access or trunk (that is, IEEE 802.1Q tagged or untagged), and
changing the type does not affect their behavior.
• You cannot change an SLT into an MLT-based SMLT by adding more ports. You must delete
the SLT and then reconfigure the port as SMLT/MLT.
• You cannot change an MLT-based SMLT into an SLT by deleting all ports but one. You must
first remove the SMLT/MLT and then reconfigure the port as SLT.
• A port cannot be configured as MLT-based SMLT and as SLT at the same time.
For information about configuring SLT, see Avaya Ethernet Routing Switch 8800/8600 Configuration
— Link Aggregation, MLT, and SMLT, NN46205-518.
SMLT and Layer 2 traffic load sharing
On the edge switch, SMLT achieves load sharing by using the MLT path selection algorithm (for a
description of the algorithm, see Avaya Ethernet Routing Switch 8800/8600 Configuration — Link
Aggregation, MLT, and SMLT, NN46205-518. Usually, the algorithm operates on a source/
destination MAC address basis or a source/destination IP address basis.
On the aggregation switch, SMLT achieves load sharing by sending all traffic destined for the SMLT
client switch directly to the SMLT client, and not over the IST trunk. The IST trunk is never used to
cross traffic to and from an SMLT dual-homed wiring closet. Traffic received on the IST by an
aggregation switch is not forwarded to SMLT links (the other aggregation switch does this), thus
eliminating the possibility of a network loop.
SMLT and Layer 3 traffic Redundant Default Gateway: VRRP
On SMLT aggregation switches, you can route VLANs that are part of an SMLT network. Routing
VLANs enables the SMLT edge network to connect to other Layer 3 networks. VRRP, which
June 2016 Planning and Engineering — Network Design
Comments on this document? infodev@avaya.com
80