CISCO MDS VSANS FCIDS

Hi Andy,

     FC address is a 24 bit address assigned by the fabric during the logon processes. This 24 bit is divided into three 8 bits as below,

8 bit domain id :Is a unique id of the switch and will be in the range 1-239.

8 bit area id  : 8 bit field ranging from 0-255

8 bit port id  : 8 bit id which may range from 0-255 . This  is used to assign ALPA (Arbitrated Loop Physical Address) also .

    Vipin V.K

Thanks Vipin for your reply.

Can you please explain what area id is?

by seeing the fcid, can we figure out where the node is connected on the fabric? by domain Id we can figure out the switch location. I dont know what area id is.

Thank you

Andy

Hi Andy,

Area ID identifies a group of switch ports,. A group of ports on the same card on a switch is an example.

By seeing seeing similar area ids we can isolate switches belong to a same card. Port ID ( ALPA address) will generally be 00 unless the device is in an Arbitrated Loop.

Vipin V.K

Cisco does things slightly differently...

By default, they use the Area and ALPA fields together to increase the port range (they have switches that can go beyond the 254 available Area addresses).  You will probably see FCIDs starting from 0000 based on when devices login to the switch.

According to the standard, Area is the port ID, not a "group of ports" and ALPA is the arbitrated loop address - arbitrated loop isn't used very much any more, hence Cisco's approach of stealing this address space to extend the number of port addresses.  You used to have a loop hanging off a single port on a switch so you needed to identify the device's location on the loop as a sub-address of the port.  You will actually see this addressing a bit more now if you use Cisco NPV - the NPV device will login the switch with 00 and then the host WWNs will get addresses like 01, 02, 03 etc (or at least that's what I remember seeing in NPV environments).

Allan.