Design Reference

In Figure 34: SPBM implementation options on page 79, node VSP-G acts as a BCB for the service,
and has no IP configuration.
B—Layer 2 VSN
A Layer 2 Virtual Services Network (VSN) bridges customer VLANs (C-VLANs) over the SPBM core
infrastructure. A Layer 2 VSN associates a C-VLAN with an I-SID, which is then virtualized across
the backbone. All VLANs in the network that share the same I-SID can participate in the same VSN.
If you use Split MultiLink Trunking (SMLT) clusters or if you want IS-IS to distribute traffic across two
equal-cost paths, then you need two backbone VLANs (B-VLAN) with a primary B-VLAN and a
secondary B-VLAN. Otherwise, you need only a single B-VLAN.
One of the key advantages of the SPBM Layer 2 VSN is that network virtualization provisioning is
achieved by configuring the edge of the network (BEBs) only. The intrusive core provisioning that
other Layer 2 virtualization technologies require is not needed when new connectivity services are
added to the SPBM network. For example, when new virtual server instances are created and need
their own VLAN instances, they are provisioned at the network edge only and do not need to be
configured throughout the rest of the network infrastructure.
Based on its I-SID scalability, this solution can scale much higher than any 802.1Q tagging-based
solution. Also, because there is no need for Spanning Tree in the core, this solution does not need
any core link provisioning for normal operation. Redundant connectivity between the C-VLAN
domain and the SPBM infrastructure can be achieved by operating two SPBM switches in switch
clustering (SMLT) mode. This allows the dual homing of any traditional link-aggregation-capable
device into an SPBM network
In Figure 34: SPBM implementation options on page 79, nodes VSP-C and VSP-D act as BEBs for
the VSN. Only these nodes have a MAC table or forwarding database for C-VLAN 10.
C—Layer 2 VSN with VLAN translation
Layer 2 VSNs with VLAN translation are basically the same as the Layer 2 VSNs, except that the
BEBs on either end of the SPBM network belong to different VLANs. With this option, you can
connect one VLAN to another VLAN. In Figure 34: SPBM implementation options on page 79, VLAN
9 connects to VLAN 19. The mechanism that connects them is that they use the same I-SID
(12990009).
D—Inter-VSN routing
Inter-VSN routing allows routing between Layer 2 VLANs with different I-SIDs. You can use Inter-
VSN routing to redistribute routes between Layer 2 VLANs. This option allows effective networking
of multiple VSNs. Where you could use Layer 2 VSN with VLAN translation to interconnect VLANs,
this option takes that concept one step further and allows you to interconnect VSNs. This option also
provides the ability to route IP traffic on Layer 2 VSNs that enter on NNIs, which is especially useful
for Layer 2 edge solutions.
As seen in Figure 34: SPBM implementation options on page 79, routing between VLANs 11 and 12
occurs on the SPBM core switch VSP-G shown in the middle of the figure. With Inter-VSN routing
enabled, VSP-G transmits traffic between VLAN 11 (I-SID 12990011) and VLAN 12 (I-SID
12990012) on the VRF instance configured. Note that for these VSNs, node VSP-G acts as a BEB.
E—Layer 3 VSN
Layer 3 VSNs are very similar to Layer 2 VSNs. The difference between the two is that Layer 2
VSNs associate I-SIDs with VLANs. Layer 3 VSNs associate I-SIDs with VRFs. With the Layer 3
VSN option, all VRFs in the network that share the same I-SID can participate in the same VSN by
SPBM design guidelines
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Network Design Reference for Avaya VSP 4000 Series January 2015
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