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Mirrored Fabric Domain ID's

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We have a mirrored/dual fabric configuration with multiple switches in each fabric. We have an odd and even fabric, with odd and even domain ID's for each switch.

The question is, does each domain ID in each fabric have to be unique? Or can both fabrics have a switch with domain ID 1, 2, 3, etc..? Someone told me that if the domain ID are the same, the fabrics will not merge if there is an ISL between them. Is that correct?

I think I explained this correctly...

Thanks
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Re: Mirrored Fabric Domain ID's

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The question is, does each domain ID in each fabric
have to be unique? Or can both fabrics have a switch
with domain ID 1, 2, 3, etc..?


What dynamox said is correct.

However, one thing to be aware of is that you may get duplicate fibre channel address (FCIDs). Which is not going to stop anything working, but it can be confusing, especially to the support centre when we are trying to figure out what is plugged in where from an emcgrab or emcreports output!

e.g. If you plugged your 2 HBAs into 2 McData switchs which each had domain ID of 1 and you used port 1 on both (most people use same port for simplicity) then your FCIDs would be identical. The domain ID makes up the first 2 digits of the FCID. If you were getting SCSI errors, the first step would be to figure out which HBA is getting the errors and we would look at its FCID to figure out the domain ID of the fabric which needs to be investigated. In this situation its a little confusing, but not a showstopper since we still have WWNs.

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Re: Mirrored Fabric Domain ID's

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you dont have to have unique domain id between the two fabrics if you are not planning to merge the two. for example i have two fabrics, each fabric consists of one 140M and two 64M. 140M is assgned domain id 1, second 64M is assigned domain id 2 and third one is assigned domain id 3. the same applies to my second fabric. i am not going to merge these two fabrics hence this works for my environment.
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Re: Mirrored Fabric Domain ID's

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The question is, does each domain ID in each fabric
have to be unique? Or can both fabrics have a switch
with domain ID 1, 2, 3, etc..?


What dynamox said is correct.

However, one thing to be aware of is that you may get duplicate fibre channel address (FCIDs). Which is not going to stop anything working, but it can be confusing, especially to the support centre when we are trying to figure out what is plugged in where from an emcgrab or emcreports output!

e.g. If you plugged your 2 HBAs into 2 McData switchs which each had domain ID of 1 and you used port 1 on both (most people use same port for simplicity) then your FCIDs would be identical. The domain ID makes up the first 2 digits of the FCID. If you were getting SCSI errors, the first step would be to figure out which HBA is getting the errors and we would look at its FCID to figure out the domain ID of the fabric which needs to be investigated. In this situation its a little confusing, but not a showstopper since we still have WWNs.

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Re: Mirrored Fabric Domain ID's

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Some additional information on this that may or may not help...

If you have your switches set to a Preferred Domain ID and the Insistent checkbox checked off the switch will always want to be that ID number. But this may or may not matter since you have to take the switch offline to change the preferred Domain ID anyway.

If you want to merge two fabrics together you just have to make sure that the switches are set to different IDs when the actual merge occurs. This may require taking one fabric down and back up again before the merge can occur.
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Re: Mirrored Fabric Domain ID's

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what does Insistent option do ?

Thanks
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Re: Mirrored Fabric Domain ID's

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My understanding is that it forces the switch to use the preferred Domain ID. When you put in a preferred Domain ID without this option you could put two switches together (ISL) and bring them online and one of them would just pick a different ID. If this option is checked the ISL links would be fractured and you would have two separate fabrics even though the switches are physically connected.

I've never actually tested this out though. Too hard to get budget for a test lab :-(
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Re: Mirrored Fabric Domain ID's

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yeah ..i hear you about the test lab. I had this interesting thing occur once. I ran an ISL from Connectrix 140M to a small 16port brocade switch, prior to connecting brocade to connectrix i logged in to brocade and assigned a domain id that was not in use, which was 4. Once i connected the two switches and fabric merged ..i looked at my brocade switch and it's domain id changed to 99. I thought it was a fluke, but when i did the same thing on my other fabric, same thing occurred. I guess it had something to do with setting 140M interoperability mode.
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Re: Mirrored Fabric Domain ID's

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It probably had to do with a combination of the interoperability mode and the Domain ID offset. I think this is normally 96 on a McData, but I don't know how it works on Brocade (although I guess I'm going to have to figure that out soon). It may have lost something in the translation and added the four to the base 96 (using some kind of option base 0 concept) to come up with 96.

I guess we would have to try that out in our multi-million dollar state of the art SAN lab :-)
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Re: Mirrored Fabric Domain ID's

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McData switches only support a domain fibre address between 61 - 7F (hex). A McData domain specified as 1 will have the fibre channel address of 61.

So when you put the Brocade switch into interop, it needs to accomodate this McData restriction. The Brocade will add 60h to the domain you specified, convert to dec.
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Re: Mirrored Fabric Domain ID's

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hmm ..so if i set my id to 4 on brocade, 60+4=64 and converted to decimal is 100. Although the id that i see on brocade is 99. My math is probably wrong :)
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