In this article, I will be discussing about two different modes that an FCF switch can operate in FCoE topology.
FCF(FCoE Forwarder) is a switch that supports both Ethernet(FCoE) functionality like FIP, DCBx, LAN protocols and FC(Fiber Channel) functionality like fabric login, zoning and name services. FCF connects the CNA on the server end to any storage array(Native FC), by bridging the gap between Ethernet LAN and storage . Dell S5000 is an example of FCF switch which can be configured in two different modes- NPG or Full Fabric mode.
Before diving into NPG mode, we need to understand N_port virtualization concept called NPIV.
NPIV – N_Port ID virtualization:
- Here a single N_port on physical host can have multiple virtual WWPNs and thereby can get multiple N_port IDs from FC switch. More info about N_port and IDs in my previous post
- In FC terminology, the FC switch will allocate only single N_port ID per interface (ie: only a single N_port ID on an F_port of FC switch). NPIV lets the FC switch to allocate multiple N_port IDs per interface/F_port.
- FC-switch should be NPIV-aware so that it can allocate multiple N_port IDs on a single F-port.
- Helps in virtualized environment where each VMs can get a virtual WWPNs, thereby unique N_port IDs per VM.
- SAN Zoning uses virtual WWPNs while configuring zoning on FCF switch.
NPG – NPIV Proxy Gateway mode:
- Cisco calls it as NPV(N_Port Virtualization). Brocade calls it as “Access Gateway“
- Switch-based solution for larger SAN deployment.
- Introduces a new port type called: NP_port.
- NP_port connects to the F_port (port on FC switch) and acts as a proxy for N_ports.
- NP_Port “looks” and “acts” like an NPIV-enabled host to the upstream F_Port.
- Hence the FC switch should have the support for NPIV so that it can assign multiple N_port IDs per F_port.
- NPG switch doesn’t participate in fabric services, doesn’t get a domain ID, doesn’t do fabric logins or assign N_port IDs to N_ports.
- Advantages of using NPG Mode:
- As the NPG switch act as “NPIV-enabled host”, there is no need for domain ID configuration on NPG switch. Helps in larger deployment where domain ID is limited.
- Usually, FC switch vendor do not support connecting to another vendor FC switch to form ISL between their E-ports. NPG helps in this deployment, where we can set one vendor FC switch in NPG mode so that it act as host to another vendor FC switch.
Below two links talks intensively about this mode with excellent analogy.
Full Fabric Mode:
In Full Fabric mode, the FCF switch will provide Full Fabric Services such as Fabric Login Server, Name Server, Zoning, and ISL links etc. A Dell S5000 switch can be configured in either NPG or Full Fabric mode.