I have two very old SAN switches 4Gb/port, ibm 002005 model B32, 32 ports. OEMed from Brocade. Fabric OS version v6.4.1b, of course they don't have trunking license and not worth to buy for them.

So, I want to setup ISL between two SAN switches, make them work as one bigger switch. How the ISL between SAN switches get setup and work without trunking license?

Here is the steps I did.

The first try

1. Free up two ports for ISL(on both switches, you could use more)
2. Make sure their domain id is not same
3. Merge zoning configuration together on both SAN switches.(identical alias,zoning,zone config)
4. Connected them together via ISL

However, they seem not work as linked. I see error message on ISL ports

E-Port segmented(zone conflict)

Double checked everything, seems no type all config different on both SAN switches.

The second try

Keep the first 3 steps(from previous try) no change

1. Free up two ports for ISL(on both switches, you could use more)
2. Make sure their domain id is not same
3. Merge zoning configuration together on both SAN switches.(identical alias,zoning,zone config)

Then on the switch sw2 that goes to be subdomain to principle domain SAN switch sw1, I did:

Disable both ISL ports
Disable zoning configuration, so it becomes default, all accessable
Cleared all zoning configuration
Save config
Enable ISL ports

After the change, I see the ISL link on sw2 shows upstream, the ISL link on sw1 shows downsteam. 

Note: Only the first ISL link comes online between SAN switches will show up/downstream, other ISL links won't.

And, zoning changes does get synchronized to the other. I see they are working as I expected.

Restarted GUI windows, now I see both SAN switches are linked together(GUI window need restart to get zoning info refershed).

Compare with trunking, multiple ISL ports just have no load balancing, other than that, failover, throughput are all good.

 

For further ISL diagnostics, see an trouble shooting example Severe latency bottleneck detected on ISL link