Network Virtualization using Extreme Fabric Connect

Network Virtualization Using Extreme Fabric Connect
© 2019 Extreme Networks, Inc. All rights reserved. 43
IS-IS Overload Function
The Overload bit is special in the IS-IS LSP and used to inform the network that the advertising router is not
yet ready to forward transit traffic. The IS-IS Overload bit can be automatically set on SPB nodes during
their boot up phase, to ensure that they are not considered by other fabric nodes when computing Shortest
Path First (SPF) path calculations until after they have completed their initialization.
The same IS-IS Overload function can also be manually activated at any time and is a simple and handy
technique to isolate a specific SPB node in the network before any maintenance work is performed on it.
Tip
Extreme Networks VSP and ERS platforms both allow manually setting IS-IS Overload as
well as on startup by specifying a delay time.
Note
Note that the IS-IS Overload bit only has effect on SPB “transit” traffic; that is, traffic that
would be switched between NNI ports (e.g., on a BCB node). Traffic destined to a SPB
(BEB) node will still lead to that node even if the IS-IS Overload bit is set on it.
SPB Bridge ID
The Bridge ID of an SPB node is defined as the concatenation of the node’s Bridge Priority (2 bytes) and the
node’s IS-IS System ID (BMAC). The SPB Bridge ID is used when evaluating equal shortest paths using the Equal
Cost Tree (ECT) Algorithms.
Caution
The SPB Bridge Priority field is not currently configurable on Extreme Networks VSP
platforms and is hard coded to 00:00.
SPBM Nick-name
More commonly referred to as the SPB node’s nick-name, but referred to as the Shortest Path Source
Identifier (SPSourceID) in the IEEE standard, the nick-name is a 20-bit (two and a half octets) identifier that
must be unique to every BEB/BCB node in the SPB Fabric.
Note
In the Extreme implementation of SPBM, the nick-name can be auto-generated or else
must be manually provisioned. If provisioned, Extreme recommends to allocate the nick-
name in the format of 0.xx.xx
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where xx.xx has the same value from the IS-IS System ID
02yy.yyxx.xxss. If the IS-IS System ID was auto-generated, then use a format 1.zz.zz, where
zz.zz must be unique across the SPB fabric.
The nick-name comes into play when a fabric service needs to leverage a service-specific I-SID multicast
tree. Every I-SID multicast tree is rooted at one particular BEB node and once the shortest path tree is
computed by IS-IS, there is a need to program such tree into the data plane of all the SPB nodes forming
such tree: the root BEB, the receiving leaf BEBs, and any transit BCB node which happens to be along the
shortest path forming such tree. Every I-SID multicast tree translates into a fabric-wide unique multicast
BMAC that is simply programmed by IS-IS into the BVLAN MAC table.
The multicast BMAC is formed by combining the root BEB’s nick-name (20 bits) with the I-SID (24 bits),
plus setting of the MAC address Locally Administered Address (LAA) and Multicast bits.