Within the Cloud fabric, both the Edge port capacity (Leaf) & Fabric bandwidth (Spine) can scale out in response to demands. This means that instead of investing upfront in capacity/bandwidth, as was the case with Multi-Tier Fat tree architectures, the network fabric is elastic and can grow/stretch over time. Note that this elasticity is a function of Leaf & spine topology, not the cloud fabric itself. A 2-stage CloS built utilising Layer 3 ECMP/Link State protocols between leaf & spine, will allow scale out in much the same way.
There are a number of ways to integrate a BCF PoD into an existing network, or to enable external connectivity from the PoD. Following is a simple breakdown followed by a few notes.
BCF Connectivity Out of Fabric
Can be achieved via
- Dedicated External Tenant
- Dedicated External Segment, within a Tenant.
- Dedicated Gateway, within Segments
Note that the External gateway router always connects to a segment within a Tenant. It would never directly connect to the System Router.
The connection can be established, one of the following ways.
Ergo, when connecting to another BCF PoD, Options exist for L2 and L3.
- When connecting over L2, the fabric mode will decide how many PoDs can be interconnected.
- Be mindful that this applies to P-Fabric only (VMWare/ DC underlay Use case), and will not apply to P+V Fabric (OpenStack Use case).
- When considering “Hub & Spoke” for upto 8 BCF PoD interconnections, Note that the “Hub” Pod in this option will be spineless, made up exclusively of a dedicated pair of Leaf switches (single Leaf Group).
- There is no need for any other Layer 2/3 protocols.
- Layer 2 over Layer 3 – VXLAN, can be achieved for upto 3 PoDs. Only the switches terminating the VTEPs need to be Trident 2+ (Other switches in the fabric can be non Trident 2+).
- L3 connectivity can be achieved via BGP, OSPF (v2, as of BCF 4.6) or Static Routes
When Connecting a BCF PoD to a Non-BCF Network,
- If Layer 2 integration is sought: BCF does not run STP natively. By default, all phyiscal/virtual ports have BPDU guard enabled (Configurable). To integrate at layer 2, BPDU guard will need disabling, and a VLAN will need to be added with membership of all Core L2 interfaces, to enable BPDU pass-through.
- for Layer 3 integration, BGP or Static Routing is available. AS of BCF 4.6, OSPF v2 is now available and supported.
The followup post to this one, discusses the Layer 3 integration option in more detail.
Hasan Mansur 