Application note: SPB-M Shortest Path Bridging-MAC Alcatel-Lucent Enterprise
Intelligent techniques are required for networks to meet these demands and maximize the available bandwidth, minimize latency and ensure stable connectivity. In response, Alcatel-Lucent Enterprise has included Shortest Path Bridging MAC in MAC mode (SPB-M) as part of the OmniSwitchTM family of products. SPB-M (IEEE 802.1aq) is a new bridging standard that combines forwarding decisions based on the Intermediate System to Intermediate System (IS-IS) routing protocol with a media access control (MAC)-in-MAC data plane (IEEE 802.1ah) to allow network operators to build larger and better-performing bridged networks compared to classical networks based on Spanning Tree Protocol (STP).
2.1 What is SPB-M?
Shortest Path Bridging-MAC (SPB-M) essentially combines two separate technologies: Provider Backbone Bridging (commonly referred to as MAC-in-MAC) and the IS-IS routing protocol, which together help build a better ‘bridged’ network.
In a traditional bridged network, STP calculates and ensures a loop-free forwarding topology in the network. Frames are initially flooded and then learned by bridges to provide connectivity between other bridges, endpoints and routers.
SPB changes this paradigm by encapsulating frames from the edge of the SPB-M network in a MAC-in-MAC header, and then transmitting them within a specially designated backbone virtual local area network (BVLAN), which in turn is controlled by a special SPB-M IS-IS instance. IS-IS controls traffic forwarding through the SPB-M network.
Each ingress frame to the SPB-M network includes a service identifier as part of its MAC-in-MAC header, called an I-SID. The I-SID denotes the network source of the frame, and represents a single bridging domain. The term for configuring matching I-SID and VLAN on a port is called the Service Access Point (SAP). When frames egress the SPB-M network, the MAC-in-MAC header is removed and the frames are forwarded using their native VLAN header.
Compared to traditional layer-2 networking technologies, there is no flooding or learning in the SPB-M backbone network because IS-IS determines the optimal shortest path connection between all off the bridges, and enforces correct traffic forwarding by controlling the MAC entries in the BVLANs of all the bridges in the backbone network. Frames that need to be transmitted to all points of a specific service are actually multicast to all member nodes of that service. The bridge at the edge of the SPB-M network will construct a multicast MAC address based on the system MAC address of that bridge and the I-SID. IS-IS maintains multicast forwarding entries for all off the services and source edge bridges in the backbone network.
Evolving Enterprise Networks with SPB-M
2.2 Why SPB-M?
SPB-M in the Alcatel-Lucent Enterprise OmniSwitch offers many advantages over classic and other modern bridged networking technologies.
- Through new extensions to IS-IS, SPB-M builds a loop-free and stable topology that uses all optimal links in the network to achieve the best utilization.
- SPB-M supports up to 16 distinct virtual forwarding topologies in the same network. This enables SPB-M to further increase overall network performance.
- SPB-M BVLANs only forward traffic injected by established neighboring links. Other traffic type on the BVLAN is dropped. The same links could simultaneously transport other 802.1Q tagged or double-tag vlans.
- 802.1Q VLANs in the backbone network can be used for other purposes, such as management or IP routing.
- SPB-M is deployed in a service-based approach. Each service is created and bound to local access ports as needed by creating SAPs. IS-IS distributes the service information and automatically builds the topologies to connect all the endpoints to the service. This is done in a non-destructive manner, allowing networks to grow in complexity without rebuilding the network itself.
- Each SPB-M service represents a single layer-2 virtual network, and the protocol can scale up to 16.7 million separate services using its 24 bit I-SID field. This easily enables highly virtualized networks that far exceed the 4K limit of the traditional VLAN tag format.
- The MAC-in-MAC encapsulation protects bridges from having to learn the entire MAC table within each service. Bridges at the edge of the network see only the MAC addresses of the services they are terminating.
- SPB-M has built-in multicast capabilities and calculates a forwarding tree per service to distribute multicast, flooded, and unknown unicast traffic. SPB-M only transmits copies of frames to the end-points of the network that have ports attached to the same service.
- SPB-M is an official standard. It fully interoperates with older standards-compliant equipment, both within the SPB-M network and when connecting other equipment to the SPB-M network. This allows administrators to deploy SPB-M in a phased approach, avoiding ripping and replacing installed networks.
- The shape and size of SPB-M backbone networks topologies are very scalable and flexible. SPB-M can be deployed in small pockets of the network or can be used to connect networks across a wide area. In fact, SPB-M can ‘flatten’ the entire network, as it can scale from the datacenter room itself, across the distribution network, to the user edge using a single protocol.
- SPB-M in the OmniSwitch takes advantage of the Alcatel-Lucent Enterprise intelligent and automated network edge configuration and security features. The features include Edge Virtual Bridging (IEEE 802.1Qbg ‘EVB’), Virtual Network Profiles (vNP) and User Network Pro les (uNP), and Alcatel-Lucent Enterprise OmniVitsaTM 2500 Virtual Machine Manager. With this suite of tools, configuring and integrating SPB-M edge networks and attached devices is highly automated and flexible.