Traditional data center networks using leaf-spine topology are based on Client –Server model with majority of the traffic from North to south bound. Recent technical advancements in Server Virtualization and Cloud Computing have improved the server resource usage by supporting multiple virtual machines per node. This resulted in new east – west traffic patterns making re-design of traditional data center networks to provide scalability and redundancy.
In a typical leaf-spine topology, using xSTP to provide loop free topology resulted in under-utilization of redundant links between switches (xSTP blocks the redundant links) and higher convergence time when there is a node/link failure. TRILL and MLAG are considered as alternate solutions which provided better utilization of redundant links while overcoming the other shortcomings of xSTP.
TRILL provides optimal pair-wise forwarding, multi-pathing for both unicast and multicast traffic with quick convergence and loop-free path. While MLAG provides multi-homing support and node level redundancy with better utilization of the redundant links in the topology.
ZebOS TRILL Integration with MLAG
TRILL with MLAG solution can be used in a deployment scenario where TRILL is deployed in core to access layer, while using MLAG to provide multi homing functionality to the end servers supporting basic LACP.
In below mentioned deployment scenario, customer edge devices are multi-homed to rbridges. All of the up-links are considered as an MLAG interface. This active-active load-sharing mechanism will improve resiliency and maximize the available network bandwidth. TRILL between core to access layer helps to provide multipathing, optimal forwarding and quicker convergence.
Key design decisions taken for integration of TRILL and MLAG:
When end host forms a multi-homed connection with multiple Edge TRILL RBridge using port-channel then TRILL hello’s sent from one Edge RBridge will not be received on other Edge RBridge. As a result every TRILL edge interface will consider itself as appointer forwarder for all the vlans. This leads to frame duplication, loop, address flip-flop and RPF check failure in TRILL cloud.
So TRILL appointed forwarder distribution logic is disabled on the access link and MLAG takes control of vlan distribution logic. TRILL will make use of the MLAG distributed vlan list for sharing its interested vlan’s to other Rbridges in the TRILL Cloud.
In case of Node or Link level failures at Access Layer, MLAG with fast timers provide faster convergence than TRILL.