There is a lot of terminology in Fibre Channel and FCoE regarding ports names. What is the difference between N Port and VN Port ? What was FC- AL, and how data are exchanged in fibre channel infrastructure ? What are 5 layers of Fibre Channel ? How does it look in FCoE ? Let’s break it down!
First of all I have to recall and explain some crucial names:
Initiator – is the device in the network that initiate data transfer (the Host)
Target – is the device which replies to Initiator queries (storage server)
FC-SW (Fibre Channel Switched) – is the 3rd version of deployment of Fibre Channel technology, predated by 1st version which was P2P – Direct Attached Storage and the 2nd one which was FC-AL (Arbitrated Loop). FC-AL was a technology consisted in communication between nodes connected to the Fibre Channel HUB in logical ring topology (similar to Ethernet token ring).
In Fibre Channel infrastructure we distinguish these ports :
N-Port – Node Port- node port connected to FC switch
F-Port – switch Fabric Port – connected to N-Port, enables connection of the end
E-Port – Expansion Port – enables connection of 2 switches
FL-Port – enables connection of Arbitrated Loop topology to the FC switch
NL-Port – Node Port connected to FC-SW via Arbitrated Loop technology
MDS Switch – Cisco solution
MDS Switch has been invented in order to deal with traffic in SAN and is connected to the Fabric Interconnect or Nexus Switch. The second side of the link is connected to the Storage Server. On MDS switch below ports can be used :
TE Port – Trunking Expansion ports – MDS switches can utilize VSAN technology, thanks to which we can deploy layer 2 separation in SAN. To forward frames EISL protocol is used. VSAN is counterpart of VLAN in LAN. EISL protocol is counterpart of 802.1q
NP – Node Proxy port – enables connection of many devices via single port what improves scalability
TF Port – Trunking Fabric Port on MDS switch, enables the end devices sending tagged frames towards MDS switch. On the end device TN Port (Trunking Node Port) is set up.
SD Port – SPAN Destination Port – enables using port analyzer towards LAN network.
FX Port – automatically discovers if port is F-Port or FL-Port
B-Port – Bridge Port enables connection of geographically distant switches
Auto Port – can operate as F,FL,E,TE or TF port
World Wide Names (WWNs)
World Wide Name is 64 or 128 bits hard coded address in every single device There are 2 types of WWNs:
World Wide Node Name – which characterizes whole fabric device eg. Host Bus Adapter card, I could compare WWNN to the serial number of each device.
World Wide Port Name – which characterizes each port in a fabric device, can be compare to MAC address in Ethernet world. If we have device with one port then nWWN and pWWN often are identical.
FCIDs – Fibre Channel IDs – dynamically acquired addresses in fiber channel environment. It is 24 bits address which consists of 3 – 8 bits elements :
Domain ID – first octet, which is being acquired by switch or host from Principle Switch when joins to the fabric. Domain ID is limited to the number from 1 up to 239.
Area ID – second octet, identifies a groups of F_ports on switches, number from 1 up to 256
Port ID – third octet, identifies a particular port in given Area ID, number from 1 up to 256
Fibre Channel architecture has 5 layers:
FC-0 – defines physical stuff, cabling, connectors, laser safety standards
FC-1 – defines transmission protocol, encoding and decoding of signals, error control
FC-2 – transport mechanism, defines framing and flow control
FC-3 – provides generic services required for fabric management (name, login, address, alias time server etc)
FC-4 – mapping of upper layer protocols to FC-2. Describes, how to map legacy protocols (like IP or iSCSI) to Fibre Channel.
Exchanging data and flow control in Fibre Channel Infrastructure
In order to provide full connection between 2 nodes in Fibre Channel topology 3 stages has to be accomplished:
1. FLOGI (fabric login) – N ports must login to attached F ports
2. PLOGI – (port login) N ports must login to its target N ports
3. PRLI (process login) – N ports exchanging information about upper layer protocols, to make sure that whole process of communication between Initiator and Target will be going properly and seamlessly.
How does it look in FCoE ?
In FCoE, which enables sending Fibre Channel frames over Ethernet and ensures lossless environment, FC-0 i FC-1 are replaced with FCoE Logical End Point which consists of Ethernet physical layer and Media Access layer. The remained layers are the same. Thanks to this FC-2, FC-3 and FC-4 are visible for SAN equipment and FCoE can operate in LAN environment also.Port World Wide Names are mapped to MAC addresses.
Ports in FCoE environment :
Initiator is called ENode (Ethernet Node). Single port of CNA (Converged Network Adapter) in ENode is called VN Port – Virtual N Port
VF Port – Virtual Fabric Port – used in order to connect end devices
VE Port – Virtual Expansion Port – used in order to connect 2 Fibre Channel switches
FIP – Fibre Channel over Ethernet Initialization Protocol is responsible for making associations between all ports in FCoE topology.