Network Virtualization using Extreme Fabric Connect

Network Virtualization Using Extreme Fabric Connect
© 2019 Extreme Networks, Inc. All rights reserved. 55
Foundations for the Service Enabled Fabric
SPB Service primitives
SPB uses IS-IS as its link state routing protocol. IS-IS was originally developed as the routing protocol for
the ISO Connectionless Network Protocol CNLP and was later extended to operate with IP around the same
time OSPF was first defined. While most enterprises are more used to using OSPF, IS-IS has always been
widely used by service providers and in many respects, is considered to be more scalable and extensible
than OSPF. When it comes to Ethernet fabrics, IS-IS is the perfect choice as it operates directly onto a Layer
2 Ethernet encapsulation (as opposed to OSPF, which operates on top of IP).
The SPB 802.1aq standard does not alter the way IS-IS operates, but rather defines new IS-IS Type-Length-
Values (TLVs) to carry SPB BVLAN, BMAC and I-SID service related information.
In an SPB Ethernet fabric, every node (BEB or BCB) has IS-IS configured globally and on each and every
NNI. The SPB BVLANs are also part of the global configuration.
This is enough for SPB to form IS-IS adjacencies and to become an Ethernet fabric where every node has
computed the IS-IS shortest path towards every other node in the fabric. At this point the Ethernet OAM
can be leveraged to perform L2pings or L2traceroutes in any of the SPB BVLANs to verify and troubleshoot
connectivity across the fabric. Note that this can be done even before configuring a single IP address or
user-VLAN or virtual network (VSN).
Currently SPB only supports a single IS-IS area and point-to-point IS-IS interfaces. This means that every
NNI interconnect must be a direct Ethernet connection or a direct LAG/MLT connection or must be seen as
an L2 point-to-point circuit, if transported over some WAN cloud. Use of the Mac-in-Mac encapsulation
implies the use of oversized Ethernet frames.
Note
The Mac-in-Mac encapsulation adds 22 bytes to a regular Ethernet frame, which means
that a native Ethernet packet with an 802.1Q tag is 1522 bytes and, once the Mac-in-Mac
encapsulation is applied, becomes 1544 bytes.
Tip
All Extreme Networks SPB-capable platforms natively support Ethernet oversize frames
and can all also operate with Jumbo MTU support in conjunction with SPB.
The SPB fabric offers two service primitives that, combined, produce all the rich VSN service types. The first
primitive is equivalent to what OSPF does for IP. Every node in the SPB fabric shares the same IS-IS LSDB.
From this, every node performs an SPF run to compute the shortest path to every other node (BMAC) in
the fabric. The result is programmed in the BVLAN unicast MAC table (just like OSPF programs IP routes in
the IP Routing table).
Tip
In the event of multiple equal cost shortest paths and if the Fabric was deployed with
more than one BVLAN, each BVLAN will be programmed with one of the available equal
cost shortest paths.
SPB adds to this capability a congruence property whereby, in the presence of equal cost shortest paths
between a pair of nodes, both nodes will select the same path in both directions within the same BVLAN
(which is not true with OSPF in the presence of ECMP paths). This is an important property that comes in to