Network Virtualization using Extreme Fabric Connect

Network Virtualization Using Extreme Fabric Connect
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Figure 14 IS-IS NNI Parallel Links
In the Extreme Networks implementation, IS-IS interface authentication is also possible using either simple
password authentication or HMAC-MD5 or HMAC-SHA256 authentication. This increases security and
ensures that only trusted SPB nodes are allowed to form an IS-IS adjacency in the SPB fabric.
Backbone Core Bridge
A Backbone Core Bridge (BCB) is an SPB node with only NNIs. It is a core node whose role is purely to
transport traffic to the destination BMAC along the IS-IS shortest path. As such, a BCB only looks at the
outer MAC header of the Mac-in-Mac encapsulated traffic it switches; it does not look at the I-SID
information and is completely unaware of the information and addressing within the virtual network (VSN)
traffic it transports. There are no VRFs or user-VLANs configured on a BCB node, and therefore the BCB
node does not learn any end-station MAC addresses nor does it hold any IP routes for the L3 VSNs it
transports. Hence the Ethernet Fabric SPB Core can scale to a virtually unlimited number of services.
Tip
An SPB BCB node is conceptually identical to an MPLS P node.
Typically, a BCB node is provisioned with one single IP interface in the default Global Routing Table (GRT),
on a circuit-less loopback, purely for management (e.g., SSH, SNMP) purposes.
Backbone Edge Bridge
A Backbone Edge Bridge (BEB) is an SPB node with both UNI and NNI interfaces. Its role is to terminate
virtual networks (VSNs) onto a locally defined VRF (in the case of L3 VSN) or user-VLANs (in the case of L2
VSN). It is the BEB’s responsibility to add or remove the Mac-in-Mac encapsulation for traffic entering or
leaving the SPB fabric. A BEB must take an active role in the existence of all the VSNs it terminates by
holding all the necessary IP routes in the VRFs as well as learning all the user MAC addresses it sees in the
user-VLANs defined on it. Naturally a BEB will have a scaling limit with the number of VRFs it supports (and
hence the number of L3 VSNs it can terminate), the number of IP routes it can scale to (and hence the
number of L3 VSNs and their cumulative number of IP routes), the number of VLANs it supports, and the
number of MAC addresses it can learn across those VLANs (and hence L2 VSNs). It is therefore important
to select the right platform to meet the required scaling needs. Note however that even if a BEB reaches its
VSN scaling limit, this is in no way limiting the wider Ethernet Fabric, as one can always provision additional
BEB nodes to scale to more VSNs over the same fabric.
In general, a BEB also performs a BCB function in that it can act as transit node and be part of the shortest
path between other SPB BEB nodes (i.e., it can also switch traffic between its NNIs). The BCB function of a
BEB node can be manually turned off by enabling the IS-IS overload bit, which will result in IS-IS not
computing any shortest paths via this BEB node.
Tip
An SPB BEB node is conceptually identical to an MPLS PE node.