Avaya 8800 Planning And Engineering, Network Design page 140

SPBM design guidelines
SPBM uses the IS-IS shortest path trees to populate forwarding tables for each participating node's
individual Backbone MAC (B-MAC) addresses. Depending on the topology, SPBM supports as
many equal cost multi path trees as there are Backbone VLAN IDs (B-VIDs) provisioned (with a
maximum of 16 B-VIDs allowed by the standard and 2 allowed in ERS 8800 release 7.1) per IS-IS
instance. IS-IS interfaces operate in point-to-point mode only, which means that for any given
Ethernet or MLT interface where IS-IS has been enabled, there can be only one IS-IS adjacency
across that interface.
B-MAC
An SPBM backbone includes Backbone Edge Bridges (BEB) and Backbone Core Bridges (BCB). A
BEB performs the same functionality as a BCB, but it also terminates one or more Virtual Service
Networks (VSN). A BCB does not terminate any VSNs and is unaware of the VSN traffic it
transports. A BCB simply knows how to reach any other BEB in the SPBM backbone.
To forward customer traffic across the service provider backbone, the BEB for the VSN
encapsulates the customer Ethernet packet received at the edge into a Backbone MAC header
using the 802.1ah MAC-in-MAC encapsulation. This encapsulation hides the Customer MAC (C-
MAC) address in a Backbone MAC (B-MAC) address pair. MAC-in-MAC encapsulation defines a
BMAC-DA and BMAC-SA to identify the backbone source and destination addresses. The
originating node creates a MAC header that is used for delivery from end to end. Intermediate BCB
nodes within the SPBM backbone perform packet forwarding using BMAC-DA alone. When the
packet reaches the intended egress BEB, the Backbone MAC header is removed and the original
customer packet is forwarded onwards.
I-SID
SPBM introduces a service instance identifier called I-SID. SPBM uses I-SIDs to separate services
from the infrastructure. Once you create an SPBM infrastructure, you can add additional services
(such as VLAN extensions or VRF extensions) by provisioning the endpoints only. The SPBM
endpoints are called Backbone Edge Bridges (BEBs), which mark the boundary between the core
MAC-in-MAC SPBM domain and the edge customer 802.1Q domain. I-SIDs are provisioned on the
BEBs to be associated with a particular service instance. In the SPBM core, the bridges are referred
to as Backbone Core Bridges (BCBs). BCBs forward encapsulated traffic based on the BMAC-DA.
The SPBM B-MAC header includes an I-SID with a length of 24 bits. I-SIDs identify and transmit
virtualized traffic in an encapsulated SPBM frame. These I-SIDs are used in a Virtual Service
Network (VSN) for VLANs or VRFs across the MAC-in-MAC backbone.
• With L2 VSN, the I-SID is associated with a customer VLAN, which is then virtualized across
the backbone. L2 VSNs offer an any-any LAN service type. For L2 VSNs, each BEB can
associate an I-SID with one local VLAN.
• With L3 VSN, the I-SID is associated with a customer VRF, which is also virtualized across the
backbone. L3 VSNs are always full-mesh topologies. L3 VSNs associate one VRF per I-SID.
Encapsulating customer MAC addresses in backbone MAC addresses greatly improves network
scalability (no end-user C-MAC learning required in the core) and also significantly improves
network robustness (loops have no effect on the backbone infrastructure).
The following figure shows the components of a basic SPBM architecture.
June 2016 Planning and Engineering — Network Design
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