Fiber Channel

Addressing in Fiber channel

In a Fiber channel network, each network node has a World Wide Node Number (WWNN). Every network node has one or more World Wide Port Numbers (WWPN).
Imagine a street where many buildings have a house number. There can be some little houses for one family having one entrance as well as a big company having a house number but multiple entrances. In the latter you could drive to "XY corporation, Example Drive 38, Entrance D". 38 is the house number - or the World Wide Node Number. "D" would represent the entrance or the "World Wide Port Number".

The WWPN (World Wide Port Number) is an absolute and unique address - the world wide node address may have many ports assigned to it. Communications take place  between WWPNs. Normally, WWPNs may be derived from the WWNN. Look at the following graphic which shows a very easy configuration: (there are some vendors where the WWPN may not be derived from the WWNN of the device, this is a very simple example)

You see a storage device offering four connection ports - like a machine with four ethernet network interfaces. The device has four distinct fiberchannel interfaces and each of them has its unique World Wide Port Number (WWPN). Think of the WWPN like a MAC address on an ethernet network. It is unique. The WWNN (World Wide Node Number) is also unique - but for the device. The distinction between WWNNs and WWPNs is here in the easy example the first byte of the network address:

20 - this is a Node (WWNN)
21 - this is the WWPN of Port 1
22 - this is the WWPN of Port 2

etcetera...

With a normal computer as fiberchannel host things are a little more difficult. If you buy a Fiberchannel interface card (think of it as a network device like an Ethernet interface card) you'll get a WWNN which is unique per interface - but each port of the interface card will have its WWPN like mentioned above. So if you've bought a single-port Fiberchannel card, it will have a WWPN (Port Number) starting with hex "21", and if you've got a dual-port card it will have WWPNs whith 21 and 22:

The World Wide Node Number (WWNN) and the World Wide Port Number (WWPN) are both a World Wide Number (WWN) in the Fiberchannel Protocol.

Each WWN is 64 bit long - 8 Bytes. On Ethernet a MAC-address has  48 bits and each ethernet port has its own MAC address - the WWPN is the MAC address for fiberchannel networks. Ethernet does not know something comparable to a World Wide Node Address.

We've learned now the difference between a WWNN and a WWPN. This is fundamental in Fiberchannel's design.

But now we have to form a network with our WWNNs  so that the WWPNs may talk to each other.