Fibre Channel (SAN)

Posts: 26
Registered: ‎03-11-2010

Configuration of ISL

Hi there,

Below is the output of a portbuffershow. Some information is not included because it is not necessary for my question.

User     Port     Lx           Max/Resv    Buffer Needed          Link   Remaining
Port     Type    Mode          Buffers     Usage  Buffers     Distance  Buffers
----     ----    ----          -------     ------ -------     --------- ----------
  0        F      -               8          8       -             -
  1               -               8          0       -             -
  2        F      -               8          8       -             -
  3        E      -               8         34      34             2km
  4        F      -               8          8       -             -

10        F      -               8          8       -             -
11        E      -               8          8       8             5km
12               -               8          0       -             -

This question is about port 11. A distance of 5 km is shown, but in real life this is a distance of about 11 kilometer.

In my opinion a BB credit of 8 is too small... I think I need 18 to operate on this distance at 2 Gb/s.

Is that correct?

I would like to have some advice how to deal with it...

Reason for this question is that maximum throughput we achieve over this ISL is about 100 GB /hour

Regards, Bart

Posts: 35
Registered: ‎01-05-2005

Re: Configuration of ISL

my guess is your port 11 has ISL R_RDY mode ON (no virtual channel).   do a portcfgshow to find out.  

hope this helps.

Posts: 26
Registered: ‎03-11-2010

Re: Configuration of ISL

I see RRDY_MODE as portFlag after a portshow. I have to get rid of that flag?

FCSWITCH_HC02:sbadmin> portshow 11
portHealth: No Fabric Watch License

Authentication: None
portDisableReason: None
portCFlags: 0x1
portType:  10.0
POD Port: Port is licensed
portState: 1    Online
portPhys:  6    In_Sync
portScn:   16   E_Port    Flow control mode 2
port generation number:    1386
portId:    190b00
portIfId:    4302000f
portWwn:   20:0b:00:05:1e:90:00:1a
portWwn of device(s) connected:

Distance:  normal
portSpeed: N2Gbps

I checked both ISL ports with portcfgshow, and both have ISL R_RDY MODE configured to ON.

I think I need some further reading about this setting.

Posts: 35
Registered: ‎01-05-2005

Re: Configuration of ISL

That would explain why you only got 8 BB credits for your E port  bc you're not taking advantage of the virtual channel with your ISL.  

Posts: 26
Registered: ‎03-11-2010

Re: Configuration of ISL


Can I configure both ports with ISL R_RDY MODE off with no penalty?

I expect traffic to be interrupted while configuring both ports...

And, do I need to configure both ports with portcfglongdistance to set the distance to 11 km?

Can use some advice how to deal with this ;-)

Thanks in advance,


Posts: 35
Registered: ‎01-05-2005

Re: Configuration of ISL

unless one of the switches on the other end of your ISL is non-Brocade then I can see why R_RDY mode is ON.  But if both of your switches on either end of the ISL are Brocade, then I don't see any reason why you shouldn't turn it off.  You need to have the same settings on both ends of your ISL (wether ON or OFF). unless you have extended fabric license, portcfglongdistance do you no good.  and yes, traffic will be disrupted.

Since I do not know your environment, I can't tell you what to do.  But as a general rule, if all of your switches are Brocade brand, then yes, you should set R_RDY mode to off so you could take advantage of the virtual channels within your ISL.  You may want to consult Brocade technical support before implementing for your specific environment.

Hope this helps.

Posts: 26
Registered: ‎03-11-2010

Re: Configuration of ISL


Thanks for your explanation.

I will take this to our supplier and discuss this with them.

For now, thanks for your help.

Regards, Bart

Frequent Contributor
Posts: 76
Registered: ‎02-13-2010

Re: Configuration of ISL

Hi B.donders,

There is one reason why you may need R_RDY mode in Brocade switches. If you are using a WDM device in your ISL, some WDM devices take active part in the port buffering handling. These devices offload this task from the Brocade switch, they require the R_RDY setting to be on. It depends on your WDM device (if you have any) but it may require this setting to be ON. So check before switching it off because I have already seen that some WDMs don't work with V_RDY.

Hope it helps.


Posts: 35
Registered: ‎01-05-2005

Re: Configuration of ISL

agreed with what you said. however, in this case it would not apply based on the output of portshow provided from B.donders above.


Occasional Contributor
Posts: 7
Registered: ‎10-24-2007

Re: Configuration of ISL

A DWDM OTR card works with R-Ready off. TDM cards needs R-Ready on...

I have 8 DCX sw's with E ports using DWDM's, OTR cards.

I have R-Ready off, trunking is on.

portcfglongdistance 8/1 LD 1 300

portcdglongdistance  8/2 LD 1 300

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