The logical IS-IS interface is the mechanism that enables Fabric Extend to connect SPB fabric nodes.
Logical IS-IS interfaces perform the following functions depending on the type of core network:
In a Layer 2 core network, logical IS-IS interfaces do not use VXLAN. The tunnels are point-to-point VLAN connections so there is no need to encapsulate a VXLAN header to SPB packets. The logical IS-IS interfaces translate the Backbone VLAN IDs (B-VIDs) and map them to each of the branch provider VIDs. This use case is also called Fabric Extend VID (FE-VID).
In a Layer 3 core network, logical IS-IS interfaces create virtual IP tunnels and encapsulate SPB traffic by adding a Virtual Extensible LAN (VXLAN) header to SPB packets. This use case is also called Fabric Extend IP (FE-IP).
Fabric Extend uses virtual tunnels in Layer 3 core solutions to connect SPB fabric nodes. These nodes can stretch over IP routed campus networks, service provider Layer 2 core networks, or service provider Layer 3 core networks such as IP MPLS VPNs.
Note
You cannot use VLACP on logical IS-IS interface connections.
If the service provider has a Layer 2 core network, note the following points:
The list of VLANs should have two VLANs, not more than two or less than two. You do not have to configure the VLAN IDs (VIDs) as platforms VLANs.
Include a primary VLAN ID in the list of VLANs.
Each logical interface must have a unique set of VIDs for each port or MLT. The same VIDs however, can be reused across a different set of ports or MLTs.
Logical interface VIDs and B-VLANs cannot be the same.
Configuring the same VIDs as primary and secondary is not allowed.
The port or MLT on which the Layer 2 core IS-IS logical interface is configured cannot be part of any other user configured VLANs.
You cannot delete an MLT that is configured as a logical interface tunnel MLT.
A logical interface consists of a port/MLT and a list of VLANs, where port/MLT is the physical connectivity to the Layer 2 core network and VLANs are the list of VLANs used to transport/bridge IS-IS control packets and Mac-in-Mac data traffic.
VXLAN headers are not used in Layer 2 core Fabric Extend solutions.
IS-IS control packets are not encapsulated before they are sent over a logical interface. Instead, the VLAN in the outer Ethernet header (SPB primary bvid) is replaced by the user configured logical interface VLAN.
Spanning tree is disabled by default on port/MLT on which a Layer 2 core logical IS-IS interface is configured.
If the service provider has a Layer 3 core network, note the following points:
A logical IS-IS interface points to a remote BEB destination IP address.
Port and VLAN ID are not needed to create a logical IS-IS interface, instead they can be retrieved from the next hop of destination IP address.
IS-IS control packets (IS-IS hello, LSDB, CSNP, PSNP) are encapsulated with a VXLAN header and sent over a logical IS-IS interface.